초록 ▼

A seal backup ring assembly is provided that eliminates fluid differential pressure acting radially on the backup ring, preventing collapse of the backup ring against a shaft. The backup ring is assembled so that the initial clearance (extrusion gap) between the backup ring and relatively rotating m

A seal backup ring assembly is provided that eliminates fluid differential pressure acting radially on the backup ring, preventing collapse of the backup ring against a shaft. The backup ring is assembled so that the initial clearance (extrusion gap) between the backup ring and relatively rotating member is not affected by the differential pressure acting across the assembly. This allows for an initially small extrusion gap to be present throughout the differential pressure range.

대표청구항 ▼

1. A sealing assembly comprising: a bulkhead housing having a portion thereof exposed to a first fluid having a first fluid pressure and having a portion thereof exposed to a second fluid having a second fluid pressure, and having a locating shoulder facing in a generally axial direction;a shaft hav

1. A sealing assembly comprising: a bulkhead housing having a portion thereof exposed to a first fluid having a first fluid pressure and having a portion thereof exposed to a second fluid having a second fluid pressure, and having a locating shoulder facing in a generally axial direction;a shaft having a portion thereof exposed to said first fluid and a portion thereof exposed to said second fluid, said shaft defining an externally-oriented sealing surface of generally cylindrical form, at least part of said sealing surface being located at least partially within said bulkhead housing and being relatively movable with respect to said bulkhead housing;a retainer located radially outward of at least a portion of said shaft and surrounding at least a portion of said shaft, said retainer defining a retaining shoulder facing generally toward said locating shoulder of said bulkhead housing, and said locating shoulder facing generally toward said retaining shoulder;a backup ring of generally circular form located between said retaining shoulder and said locating shoulder, and having a first ring end with a first portion thereof facing and adjoining said retaining shoulder and a second ring end having at least a portion thereof facing and adjoining said locating shoulder, said first and second ring ends facing in generally opposite directions, said backup ring having a ring inner surface facing generally inward toward said shaft sealing surface and establishing a region of clearance therewith, and having a ring outer surface facing generally radially outward, said backup ring having radial thickness between said ring inner surface and said ring outer surface, at least a portion of said ring inner surface and at least a portion of said ring outer surface being exposed to said second fluid pressure;said region of clearance forming an extrusion gap between said ring inner surface and said shaft sealing surface at said first ring end;means for sealing establishing (a) a first inner sealing site at said first ring end sealing said extrusion gap between said ring inner surface and said shaft sealing surface, (b) a first outer sealing site at said first ring end sealing between said first ring end and said retainer, (c) a second inner sealing site at said second ring end sealing between said second ring end and said bulkhead housing, and (d) a second outer sealing site at said second ring end sealing between said second ring end and said bulkhead housing, said second inner sealing site and said second outer sealing site encircling said shaft, said second inner sealing site separated from said shaft by a radial distance and said second outer sealing site separated from said shaft by a radial distance, said radial distance separating said second outer sealing site from said shaft being greater than said radial distance separating said second inner sealing site from said shaft;said first inner and outer sealing sites sealing said first fluid pressure from said second fluid pressure and said second inner and outer sealing sites sealing said first fluid pressure from said second fluid pressure, wherein:said first outer sealing site being located generally radially outward from said first inner sealing site and said second outer sealing site being located generally radially outward from said second inner sealing site, said first inner sealing site and said first outer sealing site defining a first hydraulic area exposed to said first fluid pressure, said first fluid pressure acting over said first hydraulic area and producing a first axially-oriented hydraulic force acting on said backup ring in a first hydraulic force direction toward said locating shoulder, said first hydraulic area being an annular area located between said first inner and outer sealing sites, andsaid second inner sealing site and said second outer sealing site defining a second hydraulic area exposed to said first fluid pressure, said first fluid pressure acting on said second ring end over said second hydraulic area and producing a second axially-oriented hydraulic force acting on said backup ring in a second hydraulic force direction that is opposite to said first hydraulic force direction and toward said retaining shoulder. 2. The sealing assembly of claim 1, wherein: said means for sealing establishing said first outer sealing site being a face seal contacting and establishing sealing between said backup ring and said retainer and partitioning said first fluid pressure from said second fluid pressure, at least a portion of said retainer contacted b said first fluid and at least a portion of said retainer contacted by said second fluid, said face seal located radially outward of and encircling said sealing surface, and said sealing surface locating said backup ring laterally. 3. The sealing assembly of claim 2, further comprising: an annular seal groove formed in one of said backup ring and said retainer,wherein said face seal is located at least partially within said annular seal groove, and said annular seal groove encircling said sealing surface,a dynamic seal contacting said sealing surface and said first ring end of said backup ring establishing said first inner sealing site, and said annular seal groove located radially outward of said dynamic seal. 4. The sealing assembly of claim 3, wherein said ring inner surface of said backup ring establishes a bearing relationship with said shaft, and locates said backup ring radially with respect to said shaft, said ring inner surface located in intermediate relation to said dynamic seal and said locating shoulder of said bulkhead housing, and located in intermediate relationship to said dynamic sea and said second inner sealing site, and located in intermediate relationship to said dynamic seal and said second outer sealing site, no portion of said ring inner surface being exposed to said first fluid pressure. 5. The sealing assembly of claim 1, wherein said first fluid pressure is greater than said second fluid pressure, at least a portion of said retainer being exposed to said first fluid and said first fluid pressure, at least a portion of said retaining shoulder being exposed to said second fluid and said second fluid pressure, and a portion of said bulkhead housing located radially inward of said second inner sealing site being exposed to said second fluid and said second fluid pressure. 6. The sealing assembly of claim 1, wherein said retaining shoulder of said retainer is separated from said locating shoulder of said bulkhead housing by an axial dimension, and a spacer section controls said axial dimension, at least a portion of said retainer being exposed to said first fluid and at least a portion of said retainer being exposed to said second fluid. 7. The sealing assembly of claim 6, wherein said spacer section is an axially-projecting feature of said retainer, and has a spacer nose contacting said locating shoulder, at least a portion of said retainer being contacted by said first fluid and at least a portion of said retainer being contacted by said second fluid. 8. The sealing assembly of claim 1, wherein said shaft and said bulkhead housing have relative radial motion with respect to each other, and said backup ring is positioned laterally by said sealing surface and follows said relative radial motion and has relative radial motion with respect to said bulkhead housing and said retainer, said sealing surface passing completely through said backup ring from said first ring end to said second ring end, at least part of said sealing surface being located within and surrounded by at least a portion of said retaining shoulder. 9. The sealing assembly of claim 1, wherein a dynamic seal establishing said first inner sealing site, said backup ring has a bearing relationship with said shaft, said bearing relationship located in intermediate relation to said dynamic seal and said second ring end, and located in intermediate relationship to said dynamic seal and said second inner sealing site, and located in intermediate relationship to said dynamic seal and said second outer sealing site. 10. The sealing assembly of claim 1, wherein said retainer and said bulkhead housing are threadedly retained together, said bulkhead housing includes inner and outer seal grooves encircling said shaft and opening toward said second ring end of said backup ring, said outer seal groove located farther from said shaft than said inner seal groove and separated from said shaft by a radial distance, an outer balancing seal located by said outer seal groove and contacting said outer seal groove and said second ring end, an inner balancing seal located by said inner seal groove and contacting said inner seal groove and said second ring end, said second ring end having an outer peripheral edge separated from said shaft by a radial distance, said radial distance separating said outer peripheral edge from said shaft being greater than said radial distance separating said outer seal groove from said shaft. 11. The sealing assembly of claim 1, wherein said retainer includes a radially inward facing surface forming a gland bore of generally cylindrical form located in spaced relation to and encircling said shaft sealing surface; and said means for sealing establishing said first outer sealing site at said first ring end sealing between said first ring end and said retainer comprises a dynamic seal located at least partially within said gland bore, said dynamic seal has first and second seal ends, with at least part of said first seal end contacting said first fluid and at least part of said second seal end contacting said first ring end of said backup ring, said dynamic seal has a static sealing surface held in sealing contact with said gland bore of said retainer and has a dynamic sealing surface in sealing contact with said shaft sealing surface;said sealing surface locating said backup ring laterally. 12. The sealing assembly of claim 11, wherein said backup ring has an axial length between said first and second ring ends, and all of said axial length is located between said dynamic seal and said locating shoulder, no spring being located between said backup ring and said locating shoulder; said first seal end facing away from said second seal end and facing away from said first ring end of said backup ring, a portion of said second ring end of said backup ring exposed to said first fluid and said first fluid pressure and a portion of said second ring end of said backup ring exposed to said second fluid and said second fluid pressure. 13. The sealing assembly of claim 1, wherein said means for sealing comprises a dynamic seal in contacting engagement with a second portion of said first ring end of said backup ring establishing said first inner sealing site, and said dynamic seal including a dynamic sealing surface in sealing engagement with said shaft sealing surface. 14. The sealing assembly of claim 13, wherein no portion of said backup ring encircles said dynamic seal, inner and outer balancing seals in face sealing contact with said second ring end of said backup ring, said inner and outer balancing seals contacting said bulkhead housing and encircling said shaft, at least a portion of said ring outer surface located farther from said shaft than said inner and outer balancing seals, a portion of said second ring end radially inward of said inner balancing seal exposed to said second fluid and said second fluid pressure, a portion of said second ring end radially outward of said inner balancing seal and radially inward of said outer balancing seal exposed to said first fluid and said first fluid pressure, and a portion of said second ring end located radially outward of said outer balancing seal exposed to said second fluid and said second fluid pressure. 15. The sealing assembly of claim 13, wherein no portion of said dynamic seal is located between said first and second ring ends, inner and outer balancing seals in face sealing contact with said second ring end of said backup ring, said inner and outer balancing seals contacting said bulkhead housing and encircling said shaft, at least a portion of said ring outer surface located farther from said shaft than said inner and outer balancing seals, at least a portion of said second ring end exposed to said first fluid pressure and at least a portion of said second ring end being exposed to said second fluid pressure. 16. The sealing assembly of claim 1, wherein said means for sealing comprises a dynamic seal having a dynamic sealing surface in sealing contact with said shaft sealing surface, and having a first seal end exposed to said first fluid and a second seal end facing and in contact with a second portion of said first ring end of said backup ring establishing said first outer sealing site. 17. The sealing assembly of claim 16, wherein no portion of said backup ring is located between said dynamic seal and said retaining shoulder of said retainer, inner and outer balancing seals in face sealing contact with said second ring end of said backup ring, said inner and outer balancing seals contacting said bulkhead housing and encircling said shaft, at least a portion of said ring outer surface located farther from said shaft than said inner and outer balancing seals, at least a portion of said second ring end exposed to said first fluid pressure and at least a portion of said second ring end exposed to said second fluid pressure. 18. The sealing assembly of claim 16, wherein a retainer seal contacting and establishing sealing between said bulkhead housing and said retainer, at least part of said retainer seal being exposed to said second fluid, said retainer seal located directly radially outward from and encircling said dynamic seal and located directly radially outward from and encircling said sealing surface of said shaft, said sealing surface locating said backup ring laterally. 19. The sealing assembly of claim 1, wherein said means for sealing comprises: an inner balancing seal in sealing contact with said bulkhead housing and said second ring end of said backup ring establishing said second inner sealing site separated from said first inner sealing site by an axial distance;an outer balancing seal in sealing contact with said bulkhead housing and said second ring end of said backup ring establishing said second outer sealing site separated from said first outer sealing site by an axial distance, said inner and outer balancing seals encircling said shaft sealing surface; andsaid inner balancing seal located between and exposed to said first fluid and said second fluid and sealing said first fluid from said second fluid, and said outer balancing seal located between and exposed to said first fluid and said second fluid and sealing said first fluid from said second fluid, at least some of said first fluid located between said inner and outer balancing seals; a portion of said bulkhead housing radially inward of said inner balancing seal exposed to said second fluid and said second fluid pressure, a portion of said bulkhead housing radially outward of said inner balancing seal and radially inward of said outer balancing seal exposed to said first fluid and said first fluid pressure. 20. The sealing assembly of claim 19, wherein said outer balancing seal is located radially outward of and encircles said inner balancing seal. 21. The sealing assembly of claim 19, wherein said bulkhead housing includes a pressure passage exposed to said first fluid and having an opening located between said inner and outer balancing seals, said pressure passage being a cross-drilled hole located radially outward of said sealing surface of said shaft. 22. The sealing assembly of claim 1, wherein said backup ring includes a pressure port passing through said backup ring in a generally radial direction from said region of clearance to said ring outer surface, said pressure port being located between and axially spaced from said first and second outer sealing sites and between and axially spaced from said first and second inner sealing sites, and located between and axially spaced from said first and second ring ends, and located between and axially spaced from said retaining shoulder and said locating shoulder, said pressure port having first and second open ends and providing communication in a generally radially outward direction from said region of clearance to an open area located radially outward of said ring outer surface, said first open end facing radially inward toward said sealing surface of said shaft and said second open end located radially outward of said first open end and facing radially outward and facing away from said sealing surface of said shaft, said pressure port communicating said second fluid and said second fluid pressure to said open area and to said ring outer surface, causing said backup ring to be radially pressure balanced. 23. The sealing assembly of claim 1, wherein said bulkhead housing includes a pressure port communicating said second fluid pressure to said ring outer surface, said second fluid pressure being atmospheric pressure and said second fluid being atmosphere. 24. The sealing assembly of claim 1, wherein said bulkhead housing includes a pressure passage communicating said first fluid pressure to said second hydraulic area, said pressure passage being a cross-drilled hole located radially outward of said sealing surface of said shaft, at least part of said cross-drilled hole being a generally axially oriented hole located radially outward of said second inner sealing site and located radially inward of said second outer sealing site, said generally axially oriented hole having an opening facing generally toward said second ring end of said backup ring, and at least part of said cross-drilled hole being a hole that intersects said generally axially oriented hole. 25. The sealing assembly of claim 24, wherein said retainer has a generally axially oriented fluid communication hole located radially outward of said first outer sealing site, and said fluid communication hole being exposed to said first fluid and communicating said first fluid to said cross-drilled hole. 26. The sealing assembly of claim 1, wherein said first hydraulic area is substantially equal to said second hydraulic area. 27. The sealing assembly of claim 1, wherein said first ring end and said second ring end are substantially flat surfaces and said first ring end is substantially parallel to said second ring end, said shaft having an axis, said first ring end separated from said axis by a radial distance, said second ring end separated from said axis by a radial distance, and said sealing surface separated from said axis by a radial distance and locating said backup ring laterally, said radial distance separating said first ring end from said axis being no less than said radial distance separating said sealing surface from said axis and said radial distance separating said second ring end from said axis being no less than said radial distance separating said sealing surface from said axis. 28. The sealing assembly of claim 1, wherein said first inner sealing site is separated from said second inner sealing site by an axial distance,said first outer sealing site is separated from said second outer sealing site by an axial distance,said axial distance separating said first and second inner sealing sites is substantially equal to said axial distance separating said first and second outer sealing sites,a portion of said second ring end located radially inward of said second inner sealing site exposed to said second fluid and said second fluid pressure, a portion of said second ring end located radially outward of said second inner sealing site and radially inward of said second outer sealing site exposed to said first fluid and said first fluid pressure, and a portion of said second ring end located radially outward of said second outer sealing site exposed to said second fluid and said second fluid pressure, anda portion of said bulkhead housing located radially inward of said second inner sealing site exposed to said second fluid and said second fluid pressure, a portion of said bulkhead housing located radially outward of said second inner sealing site and radially inward of said second outer sealing site exposed to said first fluid and said first fluid pressure, and a portion of said bulkhead housing located radially outward of said second outer sealing site exposed to said second fluid and said second fluid pressure. 29. The sealing assembly of claim 1, wherein said backup ring has a circumference and a pattern of weakening holes in said backup ring provide said backup ring with variable stiffness about said circumference, inner and outer balancing seals contacting and sealing between said bulkhead housing and said second ring end of said backup ring, a portion of said second ring end radially inward of said inner balancing seal exposed to said second fluid and said second fluid pressure, a portion of said second ring end radially outward of said inner balancing seal and radially inward of said outer balancing seal exposed to said first fluid and said first fluid pressure, and a portion of said second ring end located radially outward of said outer balancing seal exposed to said second fluid and said second fluid pressure, and said pattern of weakening holes located between said first ring end and said inner and outer balancing seals, said weakening holes selected from a group consisting of generally radially oriented weakening holes and generally axially oriented weakening holes. 30. The sealing assembly of claim 1, wherein said backup ring has a circumference and said radial thickness of said backup ring varies about said circumference, providing said backup ring with variable stiffness about said circumference, said inner and outer ring surfaces separated by a radial distance, said radial thickness being said radial distance separating said ring inner surface and said ring outer surface. 31. The sealing assembly of claim 1, wherein said retainer has an internal retainer cavity formed at least in part by said retaining shoulder, and formed at least in part by a radially inwardly facing retainer cavity surface, said radially inwardly facing retainer cavity surface encircles at least part of said backup ring. 32. The sealing assembly of claim 1, wherein said retainer has an internal retainer cavity formed at least in part by said retaining shoulder, and formed at least in part by a radially inwardly facing retainer cavity surface, at least part of said radially inwardly facing retainer cavity surface exposed to said second fluid and encircling at least part of said backup ring, and at least part of said retainer exposed to said first fluid. 33. The sealing assembly of claim 1, wherein an innermost surface of said bulkhead housing facing generally toward said shaft and exposed to said second fluid, said ring outer surface located radially outward of said ring inner surface and radially outward of said innermost surface of said bulkhead housing, wherein a pressure port passes through at least a portion of said backup ring in a generally radial direction, communicating from said region of clearance between said ring inner surface and said sealing surface of said shaft, said pressure port located between said first and second ring ends of said backup ring and spaced away from said second ring end and located between said first ring end and said second inner sealing site and between said first ring end and said second outer sealing site, and having an inwardly facing open end and an outwardly facing open end, said pressure port extending between said inwardly facing open end and said outwardly facing open end, and said outwardly facing open end located radially outward from said inwardly facing open end. 34. The sealing assembly of claim 1, wherein all of said backup ring is larger than, located directly radially outward from, and encircles said sealing surface of said shaft and said sealing surface of said shaft locates said backup ring laterally. 35. The sealing assembly of claim 1, wherein all of said retainer is larger than said sealing surface of said shaft, said sealing surface of said shaft locates said backup ring laterally, at least a portion of said retainer contacted by said first fluid and at least a portion of said retainer contacted by said second fluid. 36. The sealing assembly of claim 1, wherein said sealing surface of said shaft locating said backup ring laterally and extending completely through said bulkhead housing. 37. The sealing assembly of claim 1, wherein said sealing surface of said shaft locating said backup ring laterally and extending completely through said retainer. 38. The sealing assembly of claim 1, wherein said sealing surface of said shaft locating said backup ring laterally and extending completely through said backup ring. 39. The sealing assembly of claim 1, wherein said first and second ring ends being located radially outward of and encircling said sealing surface of said shaft, said sealing surface of said shaft locating said backup ring laterally. 40. The sealing assembly of claim 1, wherein no portion of said ring outer surface of said backup ring is exposed to said first fluid, at least a portion of said retainer is exposed to said first fluid at least a portion of said retainer is exposed to said second fluid. 41. The sealing assembly of claim 1, wherein no portion of said ring inner surface of said backup ring is exposed to said first fluid pressure and at least some portion of said retainer is exposed to said first fluid pressure. 42. The sealing assembly of claim 1, wherein at least some of said first fluid is located between said second inner sealing site and said second outer sealing site, and at least some of said second hydraulic area is exposed to said first fluid, said first and second inner and outer sealing sites each being located between said first and second fluids and each sealing said first fluid from said second fluid, a portion of said second ring end located radially inward of said second inner sealing site exposed to said second fluid and said second fluid pressure, a portion of said second ring end located radially outward of said second inner sealing site and radially inward of said second outer sealing site exposed to said first fluid and said first fluid pressure, and a portion of said second ring end located radially outward of said second outer sealing site exposed to said second fluid and said second fluid pressure, anda portion of said bulkhead housing located radially inward of said second inner sealing site exposed to said second fluid and said second fluid pressure, a portion of said bulkhead housing located radially outward of said second inner sealing site and radially inward of said second outer sealing site exposed to said first fluid and said first fluid pressure, and a portion of said bulkhead housing located radially outward of said second outer sealing site exposed to said second fluid and said second fluid pressure. 43. The sealing assembly of claim 1, wherein said backup ring positioned laterally by said sealing surface of said shaft, said bulkhead housing having an innermost surface of annular form having a diameter, and said ring inner surface of said backup ring having at least one diameter, and said sealing surface having a diameter, said diameter of said sealing surface being smaller than said diameter of said innermost surface of said bulkhead housing, and no diameter of said ring inner surface being smaller than said diameter of said sealing surface. 44. The sealing assembly of claim 1, wherein said retainer includes a radially inward facing surface forming a gland bore of generally cylindrical form located in radially spaced relation to and encircling said shaft sealing surface and exposed to said first fluid and includes a gland wall facing generally toward said first ring end and exposed to said first fluid; said sealing surface locating said backup ring laterally;at least part of said retainer contacted by said second fluid;said means for sealing establishing said first outer sealing site at said first ring end sealing between said first ring end and said retainer comprises a dynamic seal located at least partially within said gland bore and at least partially between said gland wall and said first ring end, said dynamic seal has a static sealing surface held in sealing contact with said gland bore of said retainer and has a dynamic sealing surface in sealing contact with said shaft sealing surface, and said dynamic seal has a first seal end facing generally toward said gland wall and exposed to said first fluid, and has a second seal end facing and in contact with a second portion of said first ring end, said first ring end encircling said sealing surface; andsaid second portion of said first ring end facing toward said second seal end and facing toward said gland wall. 45. The sealing assembly of claim 1, wherein said retainer having an inner peripheral surface facing generally radially inward toward and surrounding at least part of said sealing surface, said inner peripheral surface contacting said first fluid, at least part of said retainer exposed to said second fluid pressure, and said sealing surface positioning said backup ring laterally. 46. The sealing assembly of claim 45, wherein said sealing surface passes completely through said inner peripheral surface of said retainer. 47. The sealing assembly of claim 1, wherein said means for sealing establishing said first outer sealing site at said first ring end sealing between said first ring end and said retainer comprises a dynamic seal, and at least part of said dynamic seal is inside said retainer, said dynamic seal in sealing contact with said sealing surface and said sealing surface locating said backup ring laterally. 48. The sealing assembly of claim 1, wherein said backup ring is inside said retainer, at least a portion of said retainer contacted by said first fluid and at least a portion of said retainer contacted by said second fluid. 49. The sealing assembly of claim 1, wherein said locating shoulder of said bulkhead housing has inner and outer seal grooves of annular form opening toward said second ring end of said backup ring and located directly radially outward from and encircling said sealing surface, said outer seal groove located directly radially outward from and encircling said inner seal groove, an inner balancing seal being located in and contacting said inner seal groove, an outer balancing seal being located in and contacting said outer seal groove, said inner and outer balancing seals contacting said second ring end of said backup ring, a pressure passage passing through at least part of said bulkhead housing and having an opening between said inner and outer balancing seals, said pressure passage communicating said first fluid pressure and said sealing surface locating said backup ring laterally. 50. The sealing assembly of claim 1, wherein said means for sealing establishing said first outer sealing site at said first ring end sealing between said first ring end and said retainer comprises a dynamic seal, said dynamic seal contacting said first ring end, said retainer, and said shaft, said backup ring located laterally by said shaft, no part of said backup ring located between said dynamic seal and said retaining shoulder of said retainer, and no part of said dynamic seal is inside any part of said backup ring. 51. The sealing assembly of claim 1, wherein said retaining shoulder encircling at least part of said sealing surface and said sealing surface locating said backup ring laterally, and said retaining shoulder facing generally toward said first portion of said first ring end. 52. The sealing assembly of claim 1, wherein said shaft sealing surface passing completely through said ring inner surface, said sealing surface locating said backup ring laterally. 53. The sealing assembly of claim 1, wherein said shaft sealing surface passing completely through said ring inner surface and passing through said backup ring from said first ring end to said second ring end, said sealing surface locating said backup ring laterally. 54. The sealing assembly of claim 1, wherein said sealing surface passes completely through said bulkhead housing and completely through said backup ring, at least part of said sealing surface encircled by said retaining shoulder, said sealing surface locating said backup ring laterally. 55. The sealing assembly of claim 1, wherein: said means for sealing establishing said first inner sealing site being a dynamic seal contacting said sealing surface and said first ring end, said means for sealing establishing said first outer sealing site being a face seal contacting and establishing sealing between said backup ring and said retainer, said face seal located radially outward from and encircling said sealing surface and located radially outward from and encircling said dynamic seal,an annular seal groove formed in said retainer and opening toward said backup ring,said face seal being located at least partially within said annular seal groove, and said annular seal groove located radially outward from encircling said sealing surface and located radially outward from and encircling said dynamic seal. 56. The sealing assembly of claim 1, wherein said shaft has an axially facing surface, and no portion of said backup ring surrounds said axially facing surface. 57. The sealing assembly of claim 1, wherein said shaft has an axially facing surface extending radially outward to and terminating at an outer peripheral edge of said axially facing surface, and no portion of said backup ring is smaller than said outer peripheral edge of said axially facing surface. 58. A sealing assembly comprising: a bulkhead housing defining a locating shoulder facing in a generally axial direction, said bulkhead housing having a portion thereof exposed to a first fluid having a first fluid pressure and having a portion thereof exposed to a second fluid having a second fluid pressure;a shaft defining an externally-oriented sealing surface of generally cylindrical form, at least part of said sealing surface being located at least partially within said bulkhead housing, and being relatively movable with respect to said bulkhead housing, said shaft having a portion thereof exposed to said first fluid and a portion thereof exposed to said second fluid;a retainer located radially outward of at least a portion of said shaft and surrounding at least part of said shaft sealing surface, and defining a retaining shoulder facing generally toward said locating shoulder of said bulkhead housing, said locating shoulder of said bulkhead housing facing in a generally axial direction toward said retaining shoulder, said retainer having a radially inward facing surface defining a gland bore of generally cylindrical form located in radially spaced relation to said shaft sealing surface and encircling said shaft sealing surface;a backup ring of generally circular form located between said retaining shoulder of said retainer and said locating shoulder of said bulkhead housing, said backup ring having a first ring end with at least a portion thereof facing said retaining shoulder and a second ring end with at least a portion thereof facing said locating shoulder, said first and second ring ends facing in generally opposite directions, said backup ring having a ring inner surface facing generally inward toward said shaft sealing surface and establishing a region of clearance therewith forming an extrusion gap between said ring inner surface and said sealing surface at said first ring end, and having a ring outer surface facing generally radially outward, said backup ring having radial thickness between said ring inner and outer surfaces, said ring inner and outer surfaces being exposed to said second fluid pressure; anda dynamic seal located at least partially within said gland bore of said retainer, said dynamic seal having a static sealing surface held in direct sealing contact with said gland bore and having a dynamic sealing surface in sealing contact with said shaft sealing surface, said dynamic seal having a first seal end exposed to said first fluid and a second seal end facing and in contact with said first ring end of said backup ring, said region of clearance located between said dynamic seal and said second ring end;said dynamic seal establishing first inner and outer sealing sites at said first ring end, said first outer sealing site located generally radially outward from said first inner sealing site, said first inner and outer sealing sites defining a first hydraulic area exposed to said first fluid pressure, said first fluid pressure acting over said first hydraulic area and producing a first axially oriented hydraulic force acting on said backup ring in a first hydraulic force direction acting generally toward said locating shoulder of said bulkhead housing. 59. The sealing assembly of claim 58, wherein said backup ring incorporates a pressure port passing from said region of clearance and through said radial thickness of said backup ring to said ring outer surface, said pressure port located between and axially spaced from said first and second ring ends, and located between and axially spaced apart from said dynamic seal and said locating shoulder, and located between and axially spaced apart from said retaining shoulder and said locating shoulder, and located between and axially spaced apart from said first outer sealing site and said second ring end, and located between and axially spaced apart from said first inner sealing site and said second ring end, said pressure port having first and second open ends, said first open end facing radially inward toward said shaft sealing surface and said second open end facing radially outward away from said shaft sealing surface, said pressure port communicating said second fluid and said second fluid pressure of to said ring outer surface, causing said backup ring to be radially pressure balanced, none of said ring outer surface being exposed to said first fluid pressure. 60. The sealing assembly of claim 58, wherein said bulkhead housing incorporates a pressure port communicating said second fluid pressure to said ring outer surface, said second fluid being atmosphere. 61. The sealing assembly of claim 58, wherein said first and second ring ends are substantially flat surfaces. 62. The sealing assembly of claim 58, wherein said first ring end is substantially parallel to said second ring end, said shaft having an axis, said first ring end separated from said axis by a radial distance, said second ring end separated from said axis by a radial distance, and said sealing surface separated from said axis by a radial distance and locating said backup ring laterally, said radial distance separating said first ring end from said axis being no less than said radial distance separating said sealing surface from said axis and said radial distance separating said second ring end from said axis being no less than said radial distance separating said sealing surface from said axis. 63. The sealing assembly of claim 58, further comprising a retainer seal contacting and establishing sealing between said bulkhead housing and said retainer and encircling said shaft sealing surface, partitioning said first fluid from said second fluid and said first fluid pressure from said second fluid pressure, said sealing surface locating said backup ring laterally. 64. The sealing assembly of claim 63, further comprising: a retainer seal groove with a supporting wall formed in one of said bulkhead housing and said retainer,wherein said retainer seal is located at least partially within said retainer seal groove, and said supporting wall and said first ring end of said backup ring are substantially axially aligned, at least a portion of said retainer and said retainer seal contacted by said first fluid, and at least a portion of said retainer and said retainer seal contacted by said second fluid. 65. The sealing assembly of claim 63, wherein said retainer seal is a face seal. 66. The sealing assembly of claim 58, wherein said backup ring has a circumference, and a pattern of weakening holes in said backup ring provide said backup ring with variable stiffness about said circumference, said weakening holes being selected from a group consisting of generally radially oriented holes and generally axially oriented holes, inner and outer balancing seals contacting and establishing sealing between said bulkhead housing and said second ring end of said backup ring, said outer balancing seal being farther from said shaft than said inner balancing seal and said first fluid pressure acting radially outward on said outer balancing seal and acting radially inward on said inward balancing seal, said weakening holes being located in intermediate relation to said dynamic seal and said inner balancing seal and located in intermediate relation to said dynamic seal and said inner balancing seal. 67. The sealing assembly of claim 58, wherein said backup ring has a circumference, a radial distance separating said ring inner and outer surfaces, said radial thickness of said backup ring and said radial distance varying about said circumference, providing said backup ring with variable stiffness about said circumference. 68. The sealing assembly of claim 58, wherein said dynamic seal establishing said first inner sealing site sealing said extrusion gap between said ring inner surface and said shaft sealing surface, and establishing said first outer sealing site sealing between said first ring end and said retainer, said extrusion gap exposed to said second fluid pressure and a portion of said dynamic seal exposed to said second fluid pressure at said extrusion gap. 69. The sealing assembly of claim 68, further comprising a retainer seal contacting and establishing sealing between said bulkhead housing and a retainer sealing surface of said retainer, said retainer seal contacting said first and second fluids, partitioning said first fluid from said second fluid and partitioning said first fluid pressure from said second fluid pressure, said retainer sealing surface being larger than said first outer sealing site, producing a retainer hydraulic area between said retainer sealing surface and said first outer sealing site, said first fluid pressure acting on said retainer hydraulic area creating a hydraulic force acting on said retainer in said first hydraulic force direction. 70. The sealing assembly of claim 68, further comprising a retainer seal contacting and establishing sealing between said bulkhead housing and said retainer and being exposed to and separating said first fluid from said second fluid, said retainer seal being a face seal. 71. The sealing assembly of claim 58, wherein said retaining shoulder of said retainer is separated from said locating shoulder of said bulkhead housing by an axial dimension, and at least a portion of said backup ring being located directly between said retaining shoulder and said locating shoulder, said at least a portion of said backup ring having an axial length between said first and second ring ends, said axial dimension separating said locating shoulder from said retaining shoulder is greater than said axial length of said at least a portion of said backup ring to allow said backup ring to move radially in response to any radial motion of said shaft, no portion of said bulkhead housing located between said backup ring and said locating shoulder and no portion of said bulkhead housing located between said backup ring and said retaining shoulder, said first fluid contacting at least part of said gland bore of said retainer, said first ring end of said backup ring adjoining said retaining shoulder and said second ring end of said backup ring adjoining said locating shoulder. 72. The sealing assembly of claim 58, wherein further comprising: inner and outer balancing seals contacting and sealing between said bulkhead housing and said second ring end of said backup ring, said outer balancing seal being farther from said shaft than said inner balancing seal,said bulkhead housing has at least one pressure passage, and said first fluid pressure is supplied to said second ring end of said backup ring through said at least one pressure passage, said pressure passage comprising a cross-drilled hole consisting of at least two intersecting holes, at least one of said intersecting holes being a generally axially oriented hole having an opening facing toward said second ring end of said backup ring and located in intermediate relation to said inner and outer balancing seals, said opening being radially outward of said inner balancing seal and being radially inward of said outer balancing seal. 73. The sealing assembly of claim 58, wherein said ring inner surface of said backup ring is located between said dynamic seal and said locating shoulder and establishes a bearing relationship with said sealing surface of said shaft, said sealing surface locating said backup ring laterally, all of said backup ring located directly radially outward of and encircling said sealing surface, and no portion of said backup ring extending axially beyond said sealing surface. 74. The sealing assembly of claim 58, wherein said retainer and said bulkhead housing are threadedly retained together, said first fluid contacting at least a portion of said retainer, and said second ring end of said backup ring facing away from said retainer. 75. The sealing assembly of claim 58, wherein said dynamic seal includes a dynamic lip having a lubricant side flank that is exposed to said first fluid and is sloped relative to said shaft sealing surface, providing gradual convergence with said shaft sealing surface, thus forming a hydrodynamic inlet that introduces a lubricating film of said first fluid between said dynamic sealing surface and said shaft sealing surface in response to relative motion between said dynamic seal and said shaft sealing surface, said dynamic lip contacting and supported by said first ring end of said backup ring and said dynamic sealing surface located in intermediate relation to said lubricant side flank and said first ring end of said backup ring, and said dynamic sealing surface located in intermediate relation to said lubricant side flank and said second ring end of said backup ring. 76. The sealing assembly of claim 58, further comprising: an inner balancing seal in sealing contact with said bulkhead housing and said second ring end of said backup ring establishing a second inner sealing site separated from said first inner sealing site by an axial distance; andan outer balancing seal in sealing contact with said bulkhead housing and said second ring end of said backup ring establishing a second outer sealing site located generally radially outward from said second inner sealing site and separated from said first outer sealing site by an axial distance,wherein said second inner and outer sealing sites define a second hydraulic area exposed to said first fluid pressure, said first fluid pressure acting over said second hydraulic area and producing a second axially-oriented hydraulic force acting on said second ring end of said backup ring in a second hydraulic force direction that is opposite said first hydraulic force direction and toward said retaining shoulder. 77. The sealing assembly of claim 76, wherein said backup ring is penetrated by a pressure port located between and axially spaced from said first and second ring ends of said backup ring, and located between said first and second outer sealing sites, and located between said retaining shoulder and said locating shoulder, and located between said dynamic seal and said inner balancing seal and between said dynamic seal and said outer balancing seal, and passing from said region of clearance to said ring outer surface, said pressure port having first and second open ends, said first open end facing radially inward toward said sealing surface of said shaft and said second open end located radially outward of said first open end and facing radially outward and facing away from said sealing surface of said shaft, said pressure port communicating said second fluid and said second fluid pressure to said ring outer surface. 78. The sealing assembly of claim 76, wherein said bulkhead housing incorporates a pressure port communicating said second fluid pressure said ring outer surface, said second fluid being atmosphere. 79. The sealing assembly of claim 76, wherein said bulkhead housing incorporates a pressure passage communicating said first fluid pressure to said second hydraulic area, said pressure passage comprising at least one hole in said bulkhead housing having an open end facing toward said second ring end of said backup ring, said open end of said pressure passage separated from said shaft by a radial distance, said inner balancing seal separated from said shaft by a radial distance, said outer balancing seal separated from said shaft by a radial distance, said radial distance separating said open end of said pressure passage from said shaft being greater than said radial distance separating said inner balancing seal from said shaft and being less than said radial distance separating said outer balancing seal from said shaft. 80. The sealing assembly of claim 76, wherein said first hydraulic area is substantially equal to said second hydraulic area. 81. The sealing assembly of claim 76, wherein said axial distance separating said first inner sealing site from said second inner sealing site is substantially equal to said axial distance separating said first outer sealing site from said second outer sealing site, a portion of said second ring end located radially inward of said second inner sealing site exposed to said second fluid and said second fluid pressure, a portion of said second ring end located radially outward of said second inner sealing site and radially inward of said second outer sealing site exposed to said first fluid and said first fluid pressure, and a portion of said second ring end located radially outward of said second outer sealing site exposed to said second fluid and said second fluid pressure, anda portion of said bulkhead housing located radially inward of said second inner sealing site exposed to said second fluid and said second fluid pressure, a portion of said bulkhead housing located radially outward of said second inner sealing site and radially inward of said second outer sealing site exposed to said first fluid and said first fluid pressure, and a portion of said bulkhead housing located radially outward of said second outer sealing site exposed to said second fluid and said second fluid pressure. 82. The sealing assembly of claim 76, wherein said shaft sealing surface passing through said backup ring from said first ring end to said second ring end and passing completely through said ring inner surface, said sealing surface locating said backup ring laterally, and at least part of said second ring end of said backup ring located farther from said shaft than said outer balancing seal. 83. The sealing assembly of claim 76, wherein all of said retainer is larger than said sealing surface of said shaft; a radial distance separating said ring outer surface from said shaft, a radial distance separating said outer balancing seal from said shaft, and a radial distance separating said inner balancing seal from said shaft, said radial distance separating said ring outer surface from said shaft being greater than said radial distance separating said outer balancing seal from said shaft and being greater than said radial distance separating said inner balancing seal from said shaft, said radial distance separating said outer balancing seal from said shaft being greater than said radial distance separating said inner balancing seal from said shaft, said sealing surface of said shaft locating said backup ring laterally. 84. The sealing assembly of claim 76, wherein said sealing surface of said shaft extending completely through said bulkhead housing, said sealing surface locating said backup ring laterally. 85. The sealing assembly of claim 76, wherein no portion of said backup ring encircles said dynamic seal, said second ring end of said backup ring having an outer peripheral edge spaced from said shaft by a radial distance, said outer balancing seal spaced from said shaft by a radial distance, said radial distance spacing said outer peripheral edge from said shaft being greater than said radial distance spacing said outer balancing seal from said shaft. 86. The sealing assembly of claim 76, wherein said outer balancing seal is located radially outward of and encircles said inner balancing seal, a portion of said second ring end radially inward of said inner balancing seal exposed to said second fluid and said second fluid pressure, a portion of said second ring end radially outward of said inner balancing seal and radially inward of said outer balancing seal exposed to said first fluid and said first fluid pressure, and a portion of said second ring end located radially outward of said outer balancing seal exposed to said second fluid and said second fluid pressure. 87. The sealing assembly of claim 86, wherein said inner and outer balancing seals are located radially outward of and encircle said sealing surface of said shaft. 88. The sealing assembly of claim 76, wherein said bulkhead housing includes a pressure passage exposed to said first fluid and having an opening located between said inner and outer balancing seals, said pressure passage being a cross-drilled hole, a portion of said bulkhead housing radially inward of said inner balancing seal exposed to said second fluid and said second fluid pressure, a portion of said bulkhead housing radially outward of said inner balancing seal and radially inward of said outer balancing seal exposed to said first fluid and said first fluid pressure, and a portion of said bulkhead housing located radially outward of said outer balancing seal exposed to said second fluid and said second fluid pressure. 89. The sealing assembly of claim 76, wherein at least some of said first fluid is located between said inner and outer balancing seals, said inner and outer balancing seals each being located between and exposed to said first and second fluids and each sealing said first fluid from said second fluid. 90. The sealing assembly of claim 76, wherein said bulkhead housing having an innermost surface of annular form having a diameter, and said ring inner surface of said backup ring having a diameter, said diameter of said ring inner surface of said backup ring being smaller than said diameter of said innermost surface of said bulkhead housing, and at least part of said innermost surface of said bulkhead housing exposed to said second fluid and said second fluid pressure, at least a part of said locating shoulder located radially outward of said inner balancing seal exposed to said first fluid pressure, and at least a part of said locating shoulder located radially outward of said outer balancing seal exposed to said second fluid pressure. 91. The sealing assembly of claim 76, wherein said retainer includes a gland wall located adjacent to said gland bore and facing generally toward said first ring end and said locating shoulder, said first ring end facing generally axially toward said retainer, said dynamic seal located between said first ring end and said gland wall of said retainer. 92. The sealing assembly of claim 76, wherein said retainer having an inner peripheral surface facing generally radially inward toward and surrounding at least part of said sealing surface, said first fluid contacting said inner peripheral surface, said sealing surface locating said backup ring laterally. 93. The sealing assembly of claim 92, wherein said sealing surface passes completely through said inner peripheral surface of said retainer. 94. The sealing assembly of claim 76, wherein said backup ring is inside said retainer. 95. The sealing assembly of claim 76, wherein said locating shoulder of said bulkhead housing has inner and outer seal grooves of annular form opening toward said second ring end of said backup ring and encircling said sealing surface, said outer seal groove encircling said inner seal groove, said inner balancing seal contacting and being located at least partially in said inner seal groove, said outer balancing seal contacting and being located at least partially in said outer seal groove, a pressure passage passing through at least part of said bulkhead housing and having an opening between said inner and outer balancing seals, said second ring end facing toward said inner and outer seal grooves. 96. The sealing assembly of claim 95, where said opening between said inner and outer balancing seals is an axially oriented hole. 97. The sealing assembly of claim 76, wherein said retaining shoulder of said retainer encircling at least part of said sealing surface, said sealing surface locating said backup ring laterally. 98. The sealing assembly of claim 76, wherein said inner balancing seal separated from said shaft by a radial distance and said outer balancing seal separated from said shaft by a radial distance, said bulkhead housing including a pressure passage having an open end facing toward said second ring end of said backup ring and separated from said shaft by a radial distance, said radial distance separating said open end from said shaft being greater than said radial distance separating said inner balancing seal from said shaft and being less than said radial distance separating said outer balancing seal from said shaft, andsaid first fluid pressure conducted to said second hydraulic area by said pressure passage. 99. The sealing assembly of claim 76, wherein none of said ring inner surface being exposed to said first fluid pressure and all of said ring inner surface being exposed to said second fluid pressure. 100. The sealing assembly of claim 76, wherein said ring inner surface has at least one diametric dimension and said sealing surface of said shaft has a diameter, and no diametric dimension of said backup ring bore is smaller than said diameter of said sealing surface of said shaft. 101. The sealing assembly of claim 58, wherein said shaft sealing surface passing through said ring inner surface from said first ring end to said second ring end, said sealing surface locating said backup ring laterally. 102. The sealing assembly of claim 58, wherein said bulkhead housing having an internal bulkhead cavity formed at least in part by said locating shoulder, and formed at least in part by a radially inwardly facing bulkhead cavity surface, said radially inwardly facing bulkhead cavity surface encircling at least part of said backup ring and exposed to said second fluid and said second fluid pressure, inner and outer balancing seals in face sealing contact with said second ring end of said backup ring, said inner and outer balancing seals contacting said bulkhead housing and encircling said shaft, at least a portion of said ring outer surface located farther from said shaft than said inner and outer balancing seals, a portion of said second ring end between said inner and outer balancing seals exposed to said first fluid pressure, a portion of said second ring end radially inward of said inner balancing seal exposed to said second fluid and said second fluid pressure, and a portion of said second ring end located radially outward of said outer balancing seal exposed to said second fluid and said second fluid pressure. 103. The sealing assembly of claim 102, wherein said radially inwardly facing bulkhead cavity surface encircling at least part of said retainer and at least a portion of said retainer overhanging and encircling at least a portion of said backup ring, at least a portion of said retainer contacted by said first fluid, and at least a portion of said retainer contacted by said second fluid. 104. The sealing assembly of claim 58, wherein said retainer having an internal retainer cavity formed at least in part by said retaining shoulder, and formed at least in part by a radially inwardly facing retainer cavity surface, said radially inwardly facing retainer cavity surface encircling at least part of said backup ring. 105. The sealing assembly of claim 58, wherein said bulkhead housing having an innermost surface of annular form, and said innermost surface is larger than said sealing surface of said shaft and encircles at least part of said sealing surface, at least part of said innermost surface of said bulkhead housing exposed to said second fluid and said second fluid pressure. 106. The sealing assembly of claim 105, wherein said bulkhead housing includes a pressure port located radially outward of said innermost surface of said bulkhead housing, said pressure port communicating said second fluid to said ring outer surface. 107. The sealing assembly of claim 58, wherein all of said backup ring is larger than and located radially outward of said sealing surface of said shaft, said sealing surface locating said backup ring laterally. 108. The sealing assembly of claim 58, wherein said sealing surface of said shaft extending completely through said retainer, said sealing surface locating said backup ring laterally. 109. The sealing assembly of claim 58, wherein said sealing surface of said shaft extending completely through said backup ring, said sealing surface locating said backup ring laterally. 110. The sealing assembly of claim 58, wherein said first and second ring ends being located radially outward of and encircling said sealing surface of said shaft, said sealing surface locating said backup ring laterally. 111. The sealing assembly of claim 58, wherein said backup ring has an overall axial length between said first and second ring ends, and all of said axial length is located between said dynamic seal and said locating shoulder, inner and outer balancing seals in face sealing contact with said second ring end of said backup ring, said inner and outer balancing seals also contacting said bulkhead housing and encircling said shaft, at least a portion of said ring outer surface located farther from said shaft than said inner and outer balancing seals, a portion of said second ring end radially inward of said inner balancing seal exposed to said second fluid and said second fluid pressure, a portion of said second ring end radially outward of said inner balancing seal and radially inward of said outer balancing seal exposed to said first fluid and said first fluid pressure, and a portion of said second ring end located radially outward of said outer balancing seal exposed to said second fluid and said second fluid pressure. 112. The sealing assembly of claim 58, wherein no portion of said dynamic seal is located between said first and second ring ends, inner and outer balancing seals in face sealing contact with said second ring end of said backup ring, said inner and outer balancing seals also contacting said bulkhead housing and encircling said shaft, at least a portion of said ring outer surface located farther from said shaft than said inner and outer balancing seals, at least a portion of said second ring end exposed to said first fluid pressure and at least a portion of said second ring end exposed to said second fluid pressure. 113. The sealing assembly of claim 58, wherein no portion of said backup ring is located between said dynamic seal and said retainer, inner and outer balancing seals in face sealing contact with said second ring end of said backup ring, said inner and outer balancing seals also contacting said bulkhead housing and encircling said shaft, at least a portion of said ring outer surface located farther from said shaft than said inner and outer balancing seals, at least a portion of said second ring end exposed to said first fluid pressure and at least a portion of said second ring end exposed to said second fluid pressure. 114. The sealing assembly of claim 58, wherein no portion of said ring outer surface of said backup ring is exposed to said first fluid and no portion of said ring inner surface is exposed to said first fluid pressure, and a portion of said gland bore of said retainer is exposed to said first fluid and to said first fluid pressure, and no portion of said first ring end of said backup ring is exposed to said first fluid. 115. The sealing assembly of claim 58, wherein a retainer seal contacting and establishing sealing between said bulkhead housing and said retainer, at least part of said retainer seal being exposed to said second fluid, said retainer seal located radially outward of and encircles said dynamic seal and said sealing surface of said shaft, and said sealing surface locating said backup ring laterally. 116. The sealing assembly of claim 58, wherein no part of said dynamic seal is inside any part of said backup ring, inner and outer balancing seals in face sealing contact with said second ring end of said backup ring, said inner and outer balancing seals also contacting said bulkhead housing and encircling said shaft, at least a portion of said ring outer surface located farther from said shaft than said inner and outer balancing seals, at least a portion of said second ring end exposed to said first fluid pressure and at least a portion of said second ring end exposed to said second fluid pressure. 117. A sealing assembly comprising: a bulkhead housing of annular form having a portion thereof exposed to a first fluid having a first fluid pressure and having a portion thereof exposed to a second fluid having a second fluid pressure that is less than said first fluid pressure, and having a locating shoulder facing in a generally axial direction;a shaft having a portion thereof exposed to said first fluid and a portion thereof exposed to said second fluid, said shaft defining a sealing surface of generally cylindrical form, at least part of said sealing surface being located at least partially within said bulkhead housing and being relatively movable with respect to said bulkhead housing;a retainer of annular form located radially outward of at least a portion of said shaft and encircling said shaft, said retainer defining a retaining shoulder facing generally toward said locating shoulder of said bulkhead housing and separated from said locating shoulder by an axial dimension, said retainer having a radially inward facing surface defining a gland bore of generally cylindrical form located in radially spaced relation to said shaft sealing surface and encircling at least part of said shaft sealing surface, said locating shoulder of said bulkhead housing facing generally toward said retaining shoulder;a dynamic seal of annular form located at least partially within said gland bore, said dynamic seal having a static sealing surface held in direct sealing contact with said gland bore of said retainer and having a dynamic sealing surface in sealing contact with said sealing surface of said shaft;a backup ring of generally circular form located between said retaining shoulder and said locating shoulder, and having a first ring end with at least a portion thereof facing and adjoining said retaining shoulder and a second ring end having at least a portion thereof facing and adjoining said locating shoulder, said first and second ring ends facing in generally opposite directions, said backup ring having a ring inner surface that is larger than, and facing generally radially inward toward, said shaft sealing surface and establishing an extrusion gap clearance and a bearing relationship therewith locating said backup ring radially, said backup ring having a ring outer surface facing generally radially outward, at least a portion of said ring outer surface located between said retaining shoulder and said locating shoulder, said backup ring having radial thickness between said ring inner surface and said ring outer surface, said first ring end located radially outward of and encircling said shaft sealing surface, at least part of said sealing surface located within said ring inner surface, no portion of said backup ring located between said dynamic seal and said retaining shoulder of said retainer;said dynamic seal having a first seal end exposed to said first fluid and a second seal end facing and in contact with said first ring end of said backup ring, said second seal end of said dynamic seal facing toward said locating shoulder, said second seal end of said dynamic seal being nearer to said locating shoulder than said first seal end of said dynamic seal;said dynamic seal establishing a first inner sealing site at said first ring end sealing said extrusion gap clearance between said ring inner surface and said shaft sealing surface, said dynamic seal exposed to said second fluid pressure at said extrusion gap clearance, and said dynamic seal establishing a first outer sealing site providing sealing between said first ring end and said retainer;an inner balancing seal in face sealing contact with said bulkhead housing and said second ring end of said backup ring establishing a second inner sealing site separated from said first inner sealing site by an axial distance;an outer balancing seal in face sealing contact with said bulkhead housing and said second ring end of said backup ring establishing a second outer sealing site separated from said first outer sealing site by an axial distance, said outer balancing seal encircling said shaft and located radially outward of and encircling said inner balancing seal;said first inner and outer sealing sites and said second inner and outer sealing sites each sealing said first fluid pressure from said second fluid pressure, said first outer sealing site located generally radially outward from said first inner sealing site and said second outer sealing site located generally radially outward from said second inner sealing site, said first inner sealing site and said first outer sealing site defining a first hydraulic area exposed to said first fluid pressure, said first fluid pressure acting over said first hydraulic area and producing a first axially-oriented hydraulic force acting on said backup ring in a first hydraulic force direction, andsaid second inner sealing site and said second outer sealing site defining a second hydraulic area exposed to said first fluid pressure, said first fluid pressure acting over said second hydraulic area and producing a second axially-oriented hydraulic force acting on said backup ring in a second hydraulic force direction that is opposite to said first hydraulic force direction, said bulkhead housing having a pressure passage passing through at least part of said bulkhead housing and having an open end located between said inner and outer balancing seals, said pressure passage communicating said first fluid pressure to said second hydraulic area. 118. The sealing assembly of claim 117, wherein said ring inner surface and said ring outer surface being exposed to said second fluid pressure causing said backup ring to be radially pressure balanced. 119. The sealing assembly of claim 117, wherein said bulkhead housing and said retainer are threadedly retained together, and said first fluid contacting at least a portion of said retainer, and said second ring end of said backup ring facing away from said retainer. 120. The sealing assembly of claim 117, wherein said backup ring is penetrated by at least one pressure port located between and axially spaced from said first ring end and said second ring end, and located between and axially spaced from said dynamic seal and said locating shoulder of said bulkhead housing, and located between and axially spaced from said dynamic seal and said inner balancing seal, and located between and axially spaced from said dynamic seal and said outer balancing seal, said pressure port having generally oppositely facing first and second open ends, said first open end facing radially inward toward said sealing surface of said shaft and said second open end located radially outward of said first open end and facing radially outward away from said sealing surface of said shaft, said pressure port passing in a generally radial direction through at least a portion of said backup ring and communicating said second fluid pressure to said ring outer surface. 121. The sealing assembly of claim 117, wherein said first ring end and said second ring end are substantially flat surfaces, and said first ring end is substantially parallel to said second ring end, said inner balancing seal separated from said dynamic seal by a first axial distance and said outer balancing seal separated from said dynamic seal by a second axial distance, said first and second axial distances being equal, said shaft having an axis, said first ring end separated from said axis by a radial distance, said second ring end separated from said axis by a radial distance, and said sealing surface separated from said axis by a radial distance, said radial distance separating said first ring end from said axis being no less than said radial distance separating said sealing surface from said axis and said radial distance separating said second ring end from said axis being no less than said radial distance separating said sealing surface from said axis. 122. The sealing assembly of claim 117, wherein a component selected from a group consisting of said bulkhead housing and said retainer has an axial portion thereof located radially outward of and encircling at least part of said backup ring and establishing a region of radial clearance between said axial portion and said ring outer surface, said axial portion thereof incorporating an anti-rotation pocket, and an anti-rotation tang projecting from said backup ring engages said anti-rotation pocket, said bulkhead housing including a pressure port extending to and communicating with said region of radial clearance and communicating said second fluid pressure to said ring outer surface, said sealing surface passing completely through said backup ring and said retainer. 123. The sealing assembly of claim 117, wherein said first hydraulic area is substantially equal to said second hydraulic area. 124. The sealing assembly of claim 117, further comprising a retainer seal encircling said shaft sealing surface, contacting and establishing sealing between said bulkhead housing and said retainer, said retainer seal being a face seal. 125. The sealing assembly of claim 117, wherein said backup ring has an overall axial length between said first and second ring ends, and all of said overall axial length is located between said dynamic seal and said locating shoulder, and no portion of said backup ring encircles said dynamic seal, and no portion of said dynamic seal is located between said first and second ring ends, said second ring end of said backup ring having an outer peripheral edge spaced from said shaft by a radial distance, said outer balancing seal spaced from said shaft by a radial distance, said radial distance spacing said outer peripheral edge from said shaft being greater than said radial distance spacing said outer balancing seal from said shaft, said outer peripheral edge exposed to said second fluid pressure, and an annular portion of said second ring end between said inner and outer balancing seals exposed to said first fluid pressure. 126. The sealing assembly of claim 117, wherein said sealing surface of said shaft passing entirely through said ring inner surface, and passing completely through said backup ring from said first ring end to said second ring end, said second ring end being located radially outward of and encircling said sealing surface of said shaft, all of said backup ring being larger than and located radially outward of said sealing surface of said shaft. 127. The sealing assembly of claim 117, wherein said bulkhead housing having an innermost surface facing generally radially inward toward said shaft sealing surface, said innermost surface of said bulkhead housing being larger than said shaft sealing surface and located radially outward of and encircling at least part of said sealing surface, all of said bulkhead housing being larger than said sealing surface of said shaft, said ring inner surface of said backup ring being closer to said sealing surface, compared to said innermost surface of said bulkhead housing, said inner and outer balancing seals being located radially outward of and encircling said shaft sealing surface, said ring inner surface of said backup ring being smaller than said innermost surface of said bulkhead housing, and at least part of said innermost surface of said bulkhead housing exposed to said second fluid and said second fluid pressure and being the surface of said bulkhead located nearest to said shaft. 128. The sealing assembly of claim 127, wherein said sealing surface passes completely through said bulkhead housing. 129. The sealing assembly of claim 117, further comprising a retainer seal contacting and establishing sealing between said bulkhead housing and said retainer, said retainer seal located radially outward of and encircling said dynamic seal and said sealing surface of said shaft. 130. The sealing assembly of claim 117, wherein all of said retainer is larger than said sealing surface of said shaft and said sealing surface passes completely through said retainer. 131. The sealing assembly of claim 117, wherein said retainer includes a gland wall exposed to said first fluid and located adjacent to said dynamic seal and facing generally toward said first seal end of said dynamic seal, and facing generally toward said first ring end and said locating shoulder, said dynamic seal being located between said gland wall and said first ring end, all of said backup ring located between said dynamic seal and said locating shoulder, no part of said backup ring located between said retaining shoulder of said retainer and said dynamic seal, and said first seal end of said dynamic seal facing generally toward said gland wall. 132. The sealing assembly of claim 117, wherein said locating shoulder of said bulkhead housing has inner and outer seal grooves of annular form opening toward said second ring end of said backup ring and encircling said sealing surface, said outer seal groove encircling said inner seal groove, said inner balancing seal contacting and being located at least partially in said inner seal groove, said outer balancing seal contacting and being located at least partially in said outer seal groove, at least part of said open end of said pressure passage being located between said inner and outer seal grooves and between said inner and outer balancing seals, said second ring end of said backup ring having an outer peripheral edge spaced from said shaft by a radial distance, said outer seal groove being spaced from said shaft by a radial distance, said radial distance spacing said outer peripheral edge from said shaft being greater than said radial distance spacing said outer seal groove from said shaft. 133. The sealing assembly of claim 117, wherein said axial distance separating said locating shoulder from said retaining shoulder is controlled by a spacer section defined by a component selected from a group consisting of said retainer and said bulkhead housing, and at least a portion of said retainer is exposed to said first fluid and at least a portion of said retainer is exposed to said second fluid. 134. The sealing assembly of claim 117, wherein said ring inner surface of said backup ring is in tangential contact with said sealing surface of said shaft, forming a hydrodynamic inlet, said hydrodynamic inlet located in intermediate relation to said dynamic seal and said locating shoulder of said bulkhead housing and located in intermediate relation to said dynamic seal and said inner balancing seal and located in intermediate relation to said dynamic seal and said outer balancing seal. 135. The sealing assembly of claim 117, wherein said bulkhead housing has at least one inwardly projecting annular structure having axial thickness, and no inwardly projecting annular structure of said bulkhead housing is interposed between said first ring end of said backup ring and said retaining shoulder, and no inwardly projecting annular structure of said bulkhead housing is interposed between said second ring end of said backup ring and said locating shoulder of said bulkhead housing. 136. A sealing assembly comprising: a bulkhead housing of annular form having an axial bore, said axial bore having first and second bore portions, said first bore portion defining an enlarged cavity bore having a locating shoulder facing in a generally axial direction and said second bore portion being the smallest portion of said axial bore, said smallest portion defining the innermost surface of said bulkhead housing;a shaft having an externally-oriented sealing surface of generally cylindrical form, at least part of said sealing surface located within said enlarged cavity bore of said bulkhead housing and being relatively movable with respect to said bulkhead housing;a retainer of annular form located radially outward of and around a portion of said shaft, said retainer defining a retaining shoulder facing said locating shoulder of said bulkhead housing, said retainer including a radially inward facing gland bore located around and in radially spaced relation to said shaft sealing surface, at least a part of said sealing surface being located inside said gland bore and at least a portion of said locating shoulder facing generally toward said retaining shoulder;a backup ring of generally cylindrical form received at least partially within said enlarged cavity bore and located between said retaining shoulder and said locating shoulder, said backup ring having first and second ring ends facing in opposite directions, at least a portion of said first ring end located radially outward of and encircling said shaft sealing surface and facing and adjoining said retaining shoulder and at least a portion of said second ring end facing said locating shoulder, said backup ring having a ring inner surface that is larger than, and facing generally radially inward toward, said shaft sealing surface and establishing an extrusion gap clearance and a bearing relationship therewith locating said backup ring radially, and said backup ring having a ring outer surface facing generally radially outward;a dynamic seal of annular form located at least partially within said gland bore of said retainer, said dynamic seal having a static sealing surface held in direct sealing contact with said gland bore of said retainer and having a dynamic sealing surface in sealing contact with said shaft sealing surface, said dynamic seal having first and second seal ends, said first seal end exposed to a first fluid having a first fluid pressure and said second seal end facing and in sealing contact with said first ring end of said backup ring, said second seal end of said dynamic seal facing toward said locating shoulder, said second seal end of said dynamic seal being nearer to said locating shoulder than said first seal end of said dynamic seal, no portion of said backup ring located between said dynamic seal and said retaining shoulder of said retainer; andat least part of said innermost surface of said bulkhead housing exposed to said second fluid and said second fluid pressure. 137. The sealing assembly of claim 136, further comprising a retainer seal located radially outward of and encircling said sealing surface of said shaft and contacting and establishing sealing between said bulkhead housing and said retainer, at least a portion of said retainer and at least a portion of said retainer seal exposed to said first fluid. 138. The sealing assembly of claim 136, wherein said retaining shoulder of said retainer is separated from said locating shoulder of said bulkhead housing by an axial dimension that is greater than an axial length between said first and second ring ends of said backup ring to allow said backup ring to move radially in response to any radial motion of said shaft, at least a portion of said second ring end adjoining said locating shoulder, at least a portion of said retainer contacted by said first fluid and at least a portion of said retainer contacted by a second fluid having a second fluid pressure that is less than said first fluid pressure. 139. The sealing assembly of claim 136, further comprising: an inner balancing seal encircling said shaft and in face sealing contact with said bulkhead housing and said second ring end of said backup ring;an outer balancing seal located radially outward of and encircling said shaft and said inner balancing seal and in face sealing contact with said bulkhead housing and said second ring end of said backup ring;said ring outer surface located radially outward from said shaft, at least part of said ring outer surface located more radially outward of said shaft than said outer balancing seal; andsaid bulkhead housing having a pressure passage passing through at least part of said bulkhead housing and having an open end located between said inner and outer balancing seals, said pressure passage communicating said first fluid pressure between said inner and outer balancing seals, said inner balancing seal partitioning said first fluid pressure from a second fluid pressure of a second fluid that is less than said first fluid pressure, and said outer balancing seal partitioning said first fluid pressure from said second fluid pressure. 140. The sealing assembly of claim 139, wherein said dynamic seal establishing a first inner sealing site at said first ring end sealing said extrusion gap clearance between said ring inner surface and said shaft sealing surface, said extrusion gap clearance exposed to said second fluid pressure, said dynamic seal exposed to said second fluid pressure at said extrusion gap clearance, and said dynamic seal establishing a first outer sealing site between said first ring end and said retainer,said inner balancing seal establishing a second inner sealing site, andsaid outer balancing seal establishing a second outer sealing site, andwherein said first inner sealing site and said first outer sealing site defining a first hydraulic area exposed to said first fluid pressure, said first fluid pressure acting over said first hydraulic area and producing a first axially-oriented hydraulic force acting on said backup ring in a first hydraulic force direction, andsaid second inner sealing site and said second outer sealing site defining a second hydraulic area exposed to said first fluid pressure, said first fluid pressure acting over said second hydraulic area and producing a second axially-oriented hydraulic force acting on said backup ring in a second hydraulic force direction that is opposite to said first hydraulic force direction, said bulkhead housing having a pressure passage communicating said first fluid pressure to said second hydraulic area. 141. The sealing assembly of claim 140, wherein said first hydraulic area is substantially equal to said second hydraulic area. 142. The sealing assembly of claim 139, wherein said at least a portion of said ring inner surface and at least a portion of said ring outer surface being exposed to said second fluid pressure causing said backup ring to be substantially radially pressure balanced. 143. The sealing assembly of claim 139, wherein said backup ring is penetrated by at least one pressure port located between and axially spaced from said first ring end and said second ring end, and located between and axially spaced from said dynamic seal and said locating shoulder of said bulkhead housing, and located between and axially s aced from said dynamic seal and said inner balancing seal, and located between and axially spaced from said dynamic seal and said outer balancing seal, said pressure port having generally oppositely facing first and second open ends, said first open end facing radially inward toward said sealing surface of said shaft and said second open end located radially outward of said first open end and facing radially outward away from said sealing surface of said shaft, said pressure port passing in a generally radial direction through at least a portion of said backup ring and communicating said second fluid pressure to said ring outer surface. 144. The sealing assembly of claim 139, wherein a region of radial clearance being located between said enlarged cavity bore and said ring outer surface, said bulkhead housing including a pressure port extending to and communicating with said region of radial clearance and communicating said second fluid pressure to said ring outer surface, and said backup ring having an overall axial length, all of said overall axial length located between said dynamic seal and said second ring end. 145. The sealing assembly of claim 139, wherein said axial bore of said bulkhead housing being larger than said shaft sealing surface and located radially outward of and encircling at least part of said sealing surface, all of said bulkhead housing being larger than said sealing surface, said ring inner surface of said backup ring being closer to said sealing surface, compared to said innermost surface of said bulkhead housing, said inner and outer balancing seals being located radially outward of and encircling said shaft sealing surface, said ring inner surface of said backup ring being smaller than said second bore portion of said bulkhead housing. 146. The sealing assembly of claim 145, wherein said sealing surface passes completely through said bulkhead housing. 147. The sealing assembly of claim 139, wherein all of said retainer is larger than said sealing surface of said shaft and said sealing surface passes completely through said retainer. 148. The sealing assembly of claim 139, wherein said locating shoulder of said bulkhead housing has inner and outer seal grooves of annular form opening in a generally axial direction toward said second ring end of said backup ring and encircling said sealing surface, said outer seal groove encircling said inner seal groove, said inner balancing seal contacting and being located at least partially in said inner seal groove, said outer balancing seal contacting and being located at least partially in said outer seal groove, at least part of said open end of said pressure passage being located between said inner and outer seal grooves. 149. The sealing assembly of claim 136, wherein said backup ring has an overall axial length between said first and second ring ends, and all of said overall axial length is located between said dynamic seal and said locating shoulder, and no portion of said backup ring encircles said dynamic seal, and no portion of said dynamic seal is located between said first and second ring ends. 150. The sealing assembly of claim 136, wherein said sealing surface of said shaft passing entirely through said ring inner surface, and passing completely through said backup ring from said first ring end to said second ring end, said second ring end being located radially outward of and encircling said sealing surface of said shaft, all of said backup ring being larger than and located radially outward of said sealing surface of said shaft. 151. The sealing assembly of claim 136, wherein said retainer includes a gland wall located adjacent to said dynamic seal and facing generally toward said first seal end of said dynamic seal, and facing generally toward said first ring end and said locating shoulder, said dynamic seal located between said gland wall and said first ring end, and all of said backup ring located between said dynamic seal and said locating shoulder, said first seal end of said dynamic seal facing toward said gland wall and facing away from said locating shoulder and facing away from said first ring end of said backup ring, said retainer located radially outward of, and surrounding all of said dynamic seal. 152. The sealing assembly of claim 136, wherein said ring inner surface of said backup ring is in tangential contact with said sealing surface of said shaft, forming a hydrodynamic inlet, said hydrodynamic inlet located in intermediate relation to said dynamic seal and said locating shoulder of said bulkhead housing, inner and outer balancing seals in face sealing contact with said second ring end of said backup ring, said inner and outer balancing seals contacting said bulkhead housing and encircling said shaft, said tangential contact located in intermediate relation to said dynamic seal and said inner balancing seal and located in intermediate relation to said dynamic seal and said outer balancing seal, at least a portion of said ring outer surface located farther from said shaft than said inner and outer balancing seals. 153. A sealing assembly comprising: a bulkhead housing of annular form having a locating shoulder facing in a generally axial direction and having an innermost surface of annular form and facing generally radially inward;a retainer of annular form having a retaining shoulder facing generally toward said locating shoulder of said bulkhead housing, said retainer having a radially inwardly facing annular surface defining a gland bore;a backup ring of generally circular form, at least a portion of said backup ring located between said retaining shoulder of said retainer and said locating shoulder of said bulkhead housing, said backup ring having a first ring end with at least a portion thereof facing said retaining shoulder and a second ring end with at least a portion thereof facing said locating shoulder, said first and second ring ends facing in generally opposite directions, said backup ring having a ring inner surface facing generally inward, and having a ring outer surface facing generally radially outward, said backup ring having radial thickness between said ring inner and outer surfaces;a shaft having a sealing surface of generally cylindrical form that is smaller than said ring inner surface, at least part of said sealing surface being located within said gland bore of said retainer, at least part of said sealing surface being located within said ring inner surface of said backup ring and establishing a region of clearance therewith, at least part of said sealing surface being located radially inward of and encircled by said first ring end of said backup ring, at least part of said shaft being located within said innermost surface of said bulkhead housing;a dynamic seal having an annular static sealing surface facing generally radially outward, an annular dynamic sealing surface facing generally radially inward, and first and second seal ends, said dynamic seal located at least partially within said gland bore of said retainer, said annular static sealing surface contacting said gland bore, said annular dynamic sealing surface contacting said sealing surface of said shaft, and said second seal end facing and contacting said first ring end of said backup ring;inner and outer balancing seals encircling said shaft and contacting said bulkhead housing and said second ring end of said backup ring, said outer balancing seal located radially outward of and encircling said inner balancing seal; anda pressure passage passing through at least part of said bulkhead housing and having an open end located between said inner and outer balancing seals. 154. The sealing assembly of claim 153, wherein said first and second ring ends are substantially flat surfaces and said first ring end is substantially parallel to said second ring end, said inner balancing seal separated from said dynamic seal by a first axial distance and said outer balancing seal separated from said dynamic seal by a second axial distance, said first and second axial distances being substantially equal, at least a portion of said first seal end exposed to a first fluid and a first fluid pressure, at least a portion of said locating shoulder located radially inward of said inner balancing seal exposed to a second fluid and a second fluid pressure and at least a portion of said locating shoulder located radially outward of said inner balancing seal exposed to said first fluid pressure, and no portion of said backup ring is located between said dynamic seal and said retaining shoulder of said retainer. 155. The sealing assembly of claim 153, wherein said backup ring has an overall axial length between said first and second ring ends, and all of said overall axial length is located between said dynamic seal and said locating shoulder, and no portion of said backup ring encircles said dynamic seal, and no portion of said dynamic seal is located between said first and second ring ends, said second ring end of said backup ring having an outer peripheral edge spaced from said shaft by a radial distance, said outer balancing seal spaced from said shaft by a radial distance, said radial distance spacing said outer peripheral edge from said shaft being greater than said radial distance spacing said outer balancing seal from said shaft, said first seal end exposed to a first fluid and said outer peripheral edge exposed to a second fluid, and at least part of said second ring end exposed to said first fluid. 156. The sealing assembly of claim 153, wherein said sealing surface of said shaft passing entirely through said ring inner surface, and passing completely through said backup ring from said first ring end to said second ring end, said first and second ring ends located radially outward of and encircling said sealing surface of said shaft, all of said backup ring being larger than and located radially outward of said sealing surface of said shaft, and said sealing surface locating said backup ring laterally. 157. The sealing assembly of claim 153, wherein a component selected from a group consisting of said bulkhead housing and said retainer has an axial portion thereof located radially outward of and encircling at least part of said backup ring and establishing a region of radial clearance between said axial portion and said ring outer surface, said axial portion thereof incorporating an anti-rotation pocket, and an anti-rotation tang projecting from said backup ring engages said anti-rotation pocket, at least a portion of said retainer exposed to a first fluid having a first fluid pressure and at least a portion of said retainer exposed to a second fluid having a second fluid pressure, said first fluid pressure being greater than said second fluid pressure, said dynamic seal partitioning said first fluid pressure from said second fluid pressure. 158. The sealing assembly of claim 157, wherein said bulkhead housing includes a pressure port located radially outward of said innermost surface of said bulkhead housing, said pressure port extending to and communicating with said region of radial clearance, at least part of said innermost surface of said bulkhead housing exposed to said second fluid and said second fluid pressure. 159. The sealing assembly of claim 153, wherein said backup ring is penetrated by at least one pressure port located between and axially spaced from said first and second ring ends of said backup ring and located between and axially spaced from said dynamic seal and said locating shoulder of said bulkhead housing, and located between said dynamic seal and said inner balancing seal and between said dynamic seal and said outer balancing seal, said pressure port having generally oppositely facing first and second open ends and providing communication in a generally radial direction between said region of clearance and said ring outer surface, said first open end facing radially inward toward said sealing surface of said shaft and said second open end located radially outward of said first open end and facing radially outward away from said sealing surface of said shaft, said pressure port passing in a generally radial direction through at least a portion of said backup ring. 160. The sealing assembly of claim 153, wherein said innermost surface of said bulkhead housing is larger than said sealing surface of said shaft and is located radially outward of and encircles at least part of said sealing surface, at least part of said innermost surface exposed to said second fluid and said second fluid pressure, all of said bulkhead housing being larger than said sealing surface of said shaft, said ring inner surface of said backup ring being closer to said sealing surface, compared to said innermost surface of said bulkhead housing, said sealing surface passing completely through said bulkhead housing and locating said backup ring laterally. 161. The sealing assembly of claim 153, further comprising a retainer seal contacting said retainer and said bulkhead housing, said retainer seal located radially outward of and encircling said dynamic seal and said sealing surface of said shaft, and said sealing surface locating said backup ring laterally. 162. The sealing assembly of claim 153, wherein said inner and outer balancing seals are located radially outward of and encircle said sealing surface of said shaft. 163. The sealing assembly of claim 153, wherein all of said retainer is larger than said sealing surface of said shaft and said sealing surface locating said backup ring laterally and extending completely through said retainer. 164. The sealing assembly of claim 153, wherein said pressure passage is a cross-drilled hole, said open end being defined by a generally axially oriented portion of said cross-drilled hole. 165. The sealing assembly of claim 153, wherein said retainer includes a gland wall located adjacent to said gland bore and facing generally toward said first seal end of said dynamic seal, and facing generally toward said first ring end and said locating shoulder, said dynamic seal being located between said gland wall and said first ring end and said first seal end of said dynamic seal facing toward said gland wall and facing away from said inner and outer balancing seals, and all of said backup ring located between said dynamic seal and said locating shoulder. 166. The sealing assembly of claim 153, wherein said backup ring is located inside a component selected from a group consisting of said retainer and said bulkhead housing, said sealing surface of said shaft positioning said backup ring laterally, said retainer having an innermost inwardly facing peripheral surface having an innermost retainer diameter, said innermost inwardly facing peripheral surface and said retaining shoulder encircling said sealing surface of said shaft, said ring inner surface having a diameter, and said diameter of said ring inner surface being smaller than said innermost retainer diameter. 167. The sealing assembly of claim 153, wherein said locating shoulder of said bulkhead housing has inner and outer seal grooves of annular form opening toward said second ring end of said backup ring and encircling said sealing surface, said outer seal groove encircling said inner seal groove, said inner balancing seal contacting and being located at least partially in said inner seal groove, said outer balancing seal contacting and being located at least partially in said outer seal groove, at least part of said open end of said pressure passage being located between said inner and outer seal grooves and between said inner and outer balancing seals and encircled by said outer seal groove, and said sealing surface locating said backup ring laterally. 168. The sealing assembly of claim 153, wherein said retaining shoulder of said retainer is separated from said locating shoulder of said bulkhead housing by an axial distance and said portion of said backup ring that is located between said retaining shoulder and said locating shoulder has an axial length, said axial length being less than said axial distance separating said retaining shoulder from said locating shoulder, no portion of said bulkhead housing located directly between said second ring end and said locating shoulder, and no portion of said bulkhead housing located directly between said first ring end and said retaining shoulder, at least a portion of said retainer contacted by a first fluid having a first fluid pressure and at least a portion of said retainer contacted b a second fluid having a second fluid pressure, said first fluid pressure being greater than said second fluid pressure. 169. The sealing assembly of claim 168, wherein said axial distance separating said locating shoulder from said retaining shoulder is controlled by a spacer section defined by a component selected from a group consisting of said retainer and said bulkhead housing, at least a portion of said retainer contacted b said first fluid and at least a portion of said retainer contacted by said second fluid. 170. The sealing assembly of claim 153, wherein said ring inner surface of said backup ring is in tangential contact with said sealing surface of said shaft, forming a hydrodynamic inlet, said hydrodynamic inlet located in intermediate relation to said dynamic seal and said locating shoulder of said bulkhead housing, and located in intermediate relation to said dynamic seal and said inner balancing seal, and located in intermediate relation to said dynamic seal and said outer balancing seal. 171. The sealing assembly of claim 153, wherein said dynamic seal contacts said retainer and said shaft at said first ring end. 172. The sealing assembly of claim 153, wherein said dynamic seal contacts said retainer, said shaft and said backup ring. 173. The sealing assembly of claim 153, wherein a planar interface is present between said retaining shoulder and said backup ring, said planar interface being sealed by said dynamic seal. 174. The sealing assembly of claim 173, wherein said planar interface is axially aligned with, and located radially outward of, said second seal end. 175. The sealing assembly of claim 153, wherein said retaining shoulder adjoins said first ring end and said locating shoulder adjoins said backup ring at said second ring end, at least a portion of said retainer exposed to a first fluid having a first fluid pressure and at least a portion of said retainer exposed to a second fluid having a second fluid pressure, said first fluid pressure being greater than said second fluid pressure, a portion of said bulkhead housing radially inward from said inner balancing seal exposed to said second fluid and said second fluid pressure, a portion of said bulkhead housing radially between said inner and outer balancing seals exposed to said first fluid and said first fluid pressure, and a portion of said bulkhead housing radially outward of said outer balancing seal exposed to said second fluid and said second fluid pressure. 176. The sealing assembly of claim 153, wherein a first fluid contacts said dynamic seal, and a generally axially oriented fluid communication hole passing through at least part of said retainer is exposed to said first fluid and communicates said first fluid to said pressure passage of said bulkhead. 177. The sealing assembly of claim 153, wherein a retainer seal contacts and seals between said retainer and said bulkhead housing, and said retainer seal is radially more distant from said sealing surface compared to said outer balancing seal, and compared to said dynamic seal, and encircles part of said sealing surface, and said sealing surface locating said backup ring laterally. 178. A sealing assembly comprising: a bulkhead housing having a portion thereof exposed to a first fluid having a first fluid pressure and having a portion thereof exposed to a second fluid having a second fluid pressure, and having a locating shoulder facing in a generally axial direction;a shaft having a portion thereof exposed to said first fluid and a portion thereof exposed to said second fluid, said shaft defining a sealing surface of generally cylindrical form, at least part of said sealing surface located at least partially within said bulkhead housing and being relatively movable with respect to said bulkhead housing;a retainer of annular form located radially outward of at least a portion of said shaft and surrounding at least a portion of said shaft, said retainer defining a retaining shoulder facing generally toward said locating shoulder of said bulkhead housing;a backup ring of annular form having a first ring end with at least a portion thereof facing said retaining shoulder and a second ring end having at least a portion thereof facing said locating shoulder, said first and second ring ends facing in generally opposite directions, said backup ring having a ring inner surface facing generally inward toward said sealing surface and establishing a region of clearance therewith and a region of tangential contact therewith, and having a ring outer surface located radially outward of said ring inner surface and between said retaining shoulder and said locating shoulder and facing generally radially outward, said backup ring having radial thickness between said ring inner surface and said ring outer surface, said ring inner and outer surfaces exposed to said second fluid and said second fluid pressure, said region of tangential contact between said sealing surface of said shaft and said ring inner surface locating said backup ring laterally, said region of clearance forming an extrusion gap between said ring inner surface and said sealing surface of said shaft at said first ring end;said first ring end of said backup ring located directly radially outward of and surrounding said sealing surface;a dynamic seal contacting said sealing surface of said shaft and said first ring end of said backup ring and establishing a first inner sealing site sealing said extrusion gap between said ring inner surface and said sealing surface of said shaft, said dynamic seal or a face seal in sealing contact with said retainer and said backup ring establishing a first outer sealing site;an inner balancing seal in face sealing contact with said bulkhead housing and said second ring end of said backup ring establishing a second inner sealing site, said inner balancing seal spaced from said shaft by a radial distance, said inner balancing seal exposed to said first fluid pressure and said second fluid pressure;an outer balancing seal in face sealing contact with said bulkhead housing and said second ring end of said backup ring establishing a second outer sealing site, said outer balancing seal exposed to said first fluid pressure and said second fluid pressure, said outer balancing seal spaced from said shaft by a radial distance, said radial distance separating said outer balancing seal from said shaft being greater than said radial distance separating said inner balancing seal from said shaft;said first inner sealing site separated from said second inner sealing site by an axial distance, said first outer sealing site separated from said second outer sealing site by an axial distance, said second inner and outer sealing sites located radially outward of and encircling said shaft, said first inner and outer sealing sites and said second inner and outer sealing sites each sealing said first fluid from said second fluid, and sealing said first fluid pressure from said second fluid pressure, wherein:said first fluid pressure is greater than said second fluid pressure, said first outer sealing site located generally radially outward from said first inner sealing site and said second outer sealing site located generally radially outward from said second inner sealing site, said first inner sealing site and said first outer sealing site defining a first hydraulic area of annular form exposed to said first fluid pressure, said first fluid pressure acting over said first hydraulic area and producing a first axially-oriented hydraulic force acting on said backup ring in a first hydraulic force direction, andsaid second inner sealing site and said second outer sealing site defining a second hydraulic area of annular form exposed to said first fluid pressure, said first fluid pressure acting over said second hydraulic area and producing a second axially oriented hydraulic force acting on said backup ring in a second hydraulic force direction that is opposite to said first hydraulic force direction. 179. The sealing assembly of claim 178, wherein said bulkhead housing has an innermost surface of annular form and other surfaces of annular form, said innermost surface being closer to said shaft than said other surfaces, and being exposed to said second fluid and said second fluid pressure. 180. A sealing assembly comprising: a bulkhead housing having a portion thereof exposed to a first fluid having a first fluid pressure and having a portion thereof exposed to a second fluid having a second fluid pressure, and having a locating shoulder facing in a generally axial direction;a shaft having a portion thereof exposed to said first fluid and a portion thereof exposed to said second fluid, said shaft defining a sealing surface of generally cylindrical form, at least part of said sealing surface located at least partially within said bulkhead housing and relatively movable with respect to said bulkhead housing;a retainer of annular form located radially outward from at least a portion of said shaft and surrounding at least a portion of said shaft, said retainer defining a retaining shoulder facing generally toward said locating shoulder of said bulkhead housing and encircling a portion of said shaft;said locating shoulder facing generally toward said retaining shoulder and encircling a portion of said shaft;a backup ring of annular form having a first ring end with a portion thereof facing and adjoining said retaining shoulder and a second ring end having at least a portion thereof facing and adjoining said locating shoulder, said second ring end having an outer peripheral edge, said first and second ring ends facing in generally opposite directions, said backup ring having a ring inner surface and a ring outer surface located between said first and second ring ends, said ring inner surface facing generally inward toward said sealing surface of said shaft and establishing a region of clearance therewith and a region of tangential contact therewith, and said ring outer surface located radially outward of said ring inner surface and between said retaining shoulder and said locating shoulder, and facing generally radially outward, said backup ring having radial thickness between said ring inner surface and said ring outer surface, said ring inner and outer surfaces exposed to said second fluid and said second fluid pressure, none of said ring outer surface exposed to said first fluid pressure and none of said ring inner surface exposed to said first fluid pressure, said retainer capturing said backup ring axially relative to said bulkhead housing;said region of tangential contact between said sealing surface of said shaft and said ring inner surface locating said backup ring laterally;said region of clearance forming an extrusion gap between said ring inner surface and said sealing surface of said shaft at said first ring end;a dynamic seal establishing a first inner sealing site at said first ring end sealing said extrusion gap between said ring inner surface and said sealing surface of said shaft, a sealing element selected from a group consisting of said dynamic seal and a face seal establishing a first outer sealing site at said first ring end sealing between said first ring end and said retainer;an inner balancing seal in face sealing contact with said bulkhead housing and said second ring end of said backup ring establishing a second inner sealing site at said second ring end sealing between said second ring end and said bulkhead housing, and an outer balancing seal in face sealing contact with said bulkhead housing and said second ring end of said backup ring establishing a second outer sealing site at said second ring end sealing between said second ring end and said bulkhead housing;said outer balancing seal separated from said shaft by a radial distance and said inner balancing seal separated from said shaft by a radial distance, said radial distance separating said outer balancing seal from said shaft being greater than said radial distance separating said inner balancing seal from said shaft;said outer peripheral edge of said second ring end separated from said shaft by a radial distance, said radial distance separating said outer peripheral edge from said shaft being greater than said radial distance separating said outer balancing seal from said shaft;said first inner sealing site separated from said second inner sealing site by an axial distance, said first outer sealing site separated from said second outer sealing site by an axial distance, said second inner and outer sealing sites located radially outward of and encircling said shaft, said first inner and outer sealing sites and said second inner and outer sealing sites each sealing said first fluid from said second fluid, and sealing said first fluid pressure from said second fluid pressure;said first fluid pressure being greater than said second fluid pressure;said first outer sealing site located generally radially outward from said first inner sealing site and said second outer sealing site located generally radially outward from said second inner sealing site, said first inner sealing site and said first outer sealing site defining a first hydraulic area exposed to said first fluid pressure, said first fluid pressure acting over said first hydraulic area and producing a first axially-oriented hydraulic force acting on said backup ring in a first hydraulic force direction toward said locating shoulder, andsaid second inner sealing site and said second outer sealing site defining a second hydraulic area exposed to said first fluid pressure, said first fluid pressure acting over said second hydraulic area and producing a second axially-oriented hydraulic force acting on said backup ring in a second hydraulic force direction that is opposite to said first hydraulic force direction and toward said retaining shoulder. 181. The sealing assembly of claim 180, wherein a pressure port passing through said backup ring in a generally radial direction, communicating from said region of clearance between said ring inner surface and said sealing surface of said shaft, said pressure port located between said first and second ring ends of said backup ring and spaced from said second ring end, said pressure port located between said dynamic seal and said locating shoulder of said bulkhead housing, said pressure port located between said dynamic seal and said inner balancing seal and located between said dynamic seal and said outer balancing seal, said pressure port having an inwardly facing open end and an outwardly facing open end, said pressure port extending between said inwardly facing open end and said outwardly facing open end, and said outwardly facing open end located radially outward from said inwardly facing open end, said pressure port communicating said second fluid and said second fluid pressure to said ring outer surface. 182. The sealing assembly of claim 180, wherein said bulkhead housing includes a pressure passage communicating said first fluid and said first fluid pressure to said second hydraulic area, at least some of said first fluid located between said second inner and outer sealing sites and between said inner and outer balancing seals, at least some of said second hydraulic area exposed to said first fluid, said inner and outer balancing seals each located between and exposed to said first and second fluids and each sealing said first fluid from said second fluid. 183. The sealing assembly of claim 180, wherein said first hydraulic area is substantially equal to said second hydraulic area. 184. The sealing assembly of claim 180, wherein said backup ring includes a pressure passage from said first ring end to said second ring end, said pressure passage containing and communicating said first fluid and said first fluid pressure to said second hydraulic area, at least some of said first fluid located between said second inner and outer sealing sites and between said inner and outer balancing seals, at least some of said second hydraulic area exposed to said first fluid, said inner and outer balancing seals each located between and exposed to said first and second fluids and each sealing said first fluid from said second fluid. 185. The sealing assembly of claim 180, wherein said backup ring has an axial length between said first and second ring ends, and all of said axial length is located between said dynamic seal and said locating shoulder, all of said axial length is located between said dynamic seal and said inner balancing seal, no portion of said dynamic seal located between said first and second ring ends, no portion of said backup ring encircling said dynamic seal, and no portion of said backup ring located between said dynamic seal and said retainer, and at least a portion of said dynamic seal located inside said retainer. 186. The sealing assembly of claim 180, wherein said bulkhead housing includes a pressure passage containing said first fluid and said first fluid pressure and having an opening located between said inner and outer balancing seals and facing toward said backup ring, said opening separated from said shaft by a radial distance, said radial distance separating said opening from said shaft being greater than said radial distance separating said inner balancing seal from said shaft and being less than said radial distance separating said outer balancing seal from said shaft. 187. The sealing assembly of claim 180, wherein said retainer has a generally axially oriented fluid communication hole located radially outward of said first outer sealing site, and said fluid communication hole communicating said first fluid to a cross-drilled hole having an opening located between said inner and outer balancing seals and facing toward said backup ring, said retainer contacted by said first and second fluids. 188. The sealing assembly of claim 180, wherein said shaft has an axially facing surface, and no portion of said backup ring surrounds said axially facing surface. 189. The sealing assembly of claim 180, wherein said shaft has an axially facing surface exposed to said second fluid and terminating at an outer peripheral edge of said axially facing surface, and no portion of said backup ring is smaller than said outer peripheral edge of said axially facing surface. 190. The sealing assembly of claim 180, wherein said shaft has an axis, said retainer is separated from said axis by a radial distance, said backup ring is separated from said axis by a radial distance, and said radial distance separating said retainer from said axis is greater than said radial distance separating said backup ring from said axis, a surface of said retainer exposed to said first fluid, and said second ring end of said backup ring facing in a generally axial direction away from said retainer. 191. The sealing assembly of claim 190, wherein said sealing surface is separated from said axis by a radial distance, said radial distance separating said retainer from said axis is greater than said radial distance separating said sealing surface from said axis, and said radial distance separating said backup ring from said axis is no less than said radial distance separating said sealing surface from said axis. 192. The sealing assembly of claim 180, wherein said bulkhead housing has an innermost surface of annular form and other surfaces of annular form, said innermost surface being closer to said shaft than said other surfaces, and being exposed to said second fluid and said second fluid pressure. 193. A sealing assembly comprising: a bulkhead housing having a portion thereof exposed to a first fluid having a first fluid pressure and having a portion thereof exposed to a second fluid having a second fluid pressure, and having a locating shoulder facing in a generally axial direction;a shaft having a portion thereof exposed to said first fluid and a portion thereof exposed to said second fluid, said shaft defining a sealing surface of generally cylindrical form, at least part of said sealing surface located at least partially within said bulkhead housing and relatively movable with respect to said bulkhead housing;a retainer of annular form located radially outward from at least a portion of said shaft and surrounding at least a portion of said shaft, said retainer defining a retaining shoulder facing generally toward said locating shoulder of said bulkhead housing and encircling a portion of said shaft;said locating shoulder facing generally toward said retaining shoulder and encircling a portion of said shaft;a backup ring of annular form having a first ring end with a portion thereof facing and adjoining said retaining shoulder and a second ring end having at least a portion thereof facing and adjoining said locating shoulder, said second ring end having an outer peripheral edge, said first and second ring ends facing in generally opposite directions, said backup ring having a ring inner surface and a ring outer surface located between said first and second ring ends, said ring inner surface facing generally inward toward said sealing surface of said shaft and establishing a region of clearance therewith and a region of tangential contact therewith, and said ring outer surface located radially outward of said ring inner surface and between said retaining shoulder and said locating shoulder, and facing generally radially outward, said backup ring having radial thickness between said ring inner surface and said ring outer surface, said ring inner and outer surfaces exposed to said second fluid and said second fluid pressure, none of said ring outer surface exposed to said first fluid pressure and none of said ring inner surface exposed to said first fluid pressure, said retainer capturing said backup ring axially relative to said bulkhead housing;said region of tangential contact between said sealing surface of said shaft and said ring inner surface locating said backup ring laterally;said region of clearance forming an extrusion gap between said ring inner surface and said sealing surface of said shaft at said first ring end;a dynamic seal having a first seal end exposed to said first fluid and a second seal end facing toward said first ring end of said backup ring, said dynamic seal establishing sealing between said backup ring and said sealing surface of said shaft, thereby preventing said first fluid from escaping through said region of clearance between said ring inner surface and said sealing surface of said shaft;a sealing element selected from a group consisting of said dynamic seal and a face seal contacting said retainer and said backup ring and establishing sealing between said first ring end and said retainer and preventing said first fluid from escaping between said first ring end and said retainer;an inner balancing seal in face sealing contact with said bulkhead housing and said second ring end of said backup ring establishing sealing between said second ring end and said bulkhead housing, and an outer balancing seal in face sealing contact with said bulkhead housing and said second ring end of said backup ring establishing sealing between said second ring end and said bulkhead housing, said inner balancing seal exposed to said first and second fluids and said outer balancing seal exposed to said first and second fluids, some of said first fluid located within an annular sealed region located between said inner and outer balancing seals and located between said locating shoulder and said second ring end, said first fluid within said annular sealed region contacting an annular portion of said second ring end;said outer balancing seal separated from said shaft by a radial distance and said inner balancing seal separated from said shaft by a radial distance, said radial distance separating said outer balancing seal from said shaft being greater than said radial distance separating said inner balancing seal from said shaft;said outer peripheral edge of said second ring end separated from said shaft by a radial distance, said radial distance separating said outer peripheral edge from said shaft being greater than said radial distance separating said outer balancing seal from said shaft;said dynamic seal separated from said inner balancing seal by an axial distance, said dynamic seal separated from said outer balancing seal by an axial distance, said inner and outer balancing seals each sealing said first fluid from said second fluid, and said inner and outer balancing seals each sealing said first fluid pressure from said second fluid pressure;said first fluid pressure being greater than said second fluid pressure;said first fluid pressure acting on said dynamic seal and producing a first axially-oriented hydraulic force acting on said backup ring in a first hydraulic force direction toward said locating shoulder, and said first fluid pressure acting on said annular portion of said second ring end of said backup ring and producing a second axially-oriented hydraulic force acting on said backup ring in a second hydraulic force direction that is opposite to said first hydraulic force direction and toward said retaining shoulder. 194. The sealing assembly of claim 193, wherein, a portion of said second ring end radially inward of said inner balancing seal exposed to said second fluid and said second fluid pressure, a portion of said second ring end radially outward of said inner balancing seal and radially inward of said outer balancing seal exposed to said first fluid and said first fluid pressure, and a portion of said second ring end located radially outward of said outer balancing seal exposed to said second fluid and said second fluid pressure, anda portion of said bulkhead housing radially inward of said inner balancing seal exposed to said second fluid and said second fluid pressure, a portion of said bulkhead housing radially outward of said inner balancing seal and radially inward of said outer balancing seal exposed to said first fluid and said first fluid pressure, and a portion of said bulkhead housing located radially outward of said outer balancing seal exposed to said second fluid and said second fluid pressure. 195. A sealing assembly comprising: a bulkhead housing of annular form having a portion thereof exposed to a first fluid pressure and having a portion thereof exposed to a second fluid pressure, and having a locating shoulder facing in a generally axial direction, and having an innermost surface of annular form and facing generally radially inward, said first fluid pressure being greater than said second fluid pressure;a shaft having a portion thereof exposed to said first fluid pressure and a portion thereof exposed to said second fluid pressure, said shaft being relatively movable with respect to said bulkhead housing and defining an externally oriented surface of generally cylindrical form, at least a portion of said shaft being located within and encircled by at least a portion of said bulkhead housing;a retainer of annular form located radially outward from at least a portion of said shaft and encircling a portion of said shaft, said retainer defining a retaining shoulder facing generally toward said locating shoulder of said bulkhead housing and encircling a portion of said shaft, said retaining shoulder being axially spaced from said locating shoulder, at least a portion of said retainer being exposed to said first fluid pressure;said locating shoulder of said bulkhead housing facing generally toward said retaining shoulder of said retainer and encircling a portion of said shaft;an annular ring having a first ring end with at least a portion thereof facing and adjoining said retaining shoulder and a second ring end facing away from said retaining shoulder and having at least a portion thereof facing and adjoining said locating shoulder, said annular ring being captured axially relative to said bulkhead housing by said retainer, said second ring end having an outer peripheral edge, said first and second ring ends facing in generally opposite directions, said annular ring having a ring inner surface and a ring outer surface, said ring inner and outer surfaces encircling at least a portion of said externally oriented surface of said shaft, at least part of said externally oriented surface of said shaft being located within said ring inner surface, said ring inner surface being larger than and facing generally inward toward said externally oriented surface of said shaft and establishing a region of clearance therewith and a region of tangential contact therewith, at least part of said ring outer surface located radially outward of said ring inner surface and located in intermediate location to said retaining shoulder and said locating shoulder, and facing generally radially outward away from said externally oriented surface of said shaft, said annular ring having radial thickness between said ring inner surface and said ring outer surface, at least part of said annular ring being located inside a component selected from a group consisting of said retainer and said bulkhead housing, said ring inner surface of said annular ring being closer to said externally oriented surface of said shaft compared to said innermost surface of said bulkhead housing;said retaining shoulder of said retainer is separated from said locating shoulder of said bulkhead housing by an axial dimension and said annular ring having an axial length between said first and second ring ends, said axial dimension separating said locating shoulder from said retaining shoulder being greater than said axial length between said first and second ring ends,said region of tangential contact between said externally oriented surface of said shaft and said ring inner surface locating said annular ring laterally and at least a portion of said region of tangential contact being located in intermediate relation to said first and second ring ends, and at least a portion of said ring inner surface being located in intermediate relation to said first and second ring ends, no portion of said annular ring being located directly between said first ring end and said retaining shoulder of said retainer;a sealing element encircling a portion of said shaft and contacting said retainer and said annular ring and establishing sealing between said first ring end and said retainer, said sealing element being exposed to said first fluid pressure and preventing said first fluid pressure from escaping between said first ring end and said retainer, no portion of said annular ring being located between said sealing element and said retaining shoulder of said retainer;an inner balancing seal encircling a portion of said shaft and contacting and sealing between said bulkhead housing and said annular ring and preventing the loss of said first fluid pressure between said second ring end and said locating shoulder, and an outer balancing seal encircling a portion of said shaft and contacting said bulkhead housing and said annular ring and preventing the loss of said first fluid pressure between said second ring end and said locating shoulder, at least a portion of said second ring end and at least a portion of said ring outer surface being located farther from said shaft than said outer balancing seal, said inner balancing seal exposed to and contacted by said first and second fluids and said outer balancing seal exposed to said first fluid pressure, some of said first fluid pressure located within an annular sealed region located between said inner and outer balancing seals and located between said locating shoulder and said second ring end, said first fluid pressure within said annular sealed region acting on an annular portion of said second ring end;a pressure passage formed in said annular ring or said bulkhead housing containing said first fluid pressure and communicating said first fluid pressure to said annular sealed region, said pressure passage having an open end opening into said annular sealed region, at least part of said open end being located radially outward of said inner balancing seal and at least part of said open end being located radially inward of said outer balancing seal, said open end being separated from said shaft by a radial distance,said inner balancing seal being and located at least partially within and contacting an inner annular groove formed in one of said bulkhead housing and said annular ring, said outer balancing seal being located at least partially within and contacting an outer annular groove formed in one of said bulkhead housing and said annular ring,said outer annular groove being separated from shaft by a radial distance and said inner annular groove being separated from said shaft by a radial distance, said radial distance separating said outer annular groove from said shaft being greater than said radial distance separating said inner annular groove from said shaft,said outer balancing seal separated from said shaft by a radial distance and said inner balancing seal separated from said shaft by a radial distance, said radial distance separating said outer balancing seal from said shaft being greater than said radial distance separating said inner balancing seal from said shaft, said outer balancing seal being farther from said shaft than said inner balancing seal;said radial distance separating said open end from said shaft being greater than said radial distance separating said inner balancing seal from said shaft and being less than said radial distance separating said outer balancing seal from said shaft,said outer peripheral edge of said second ring end separated from said shaft by a radial distance, said radial distance separating said outer peripheral edge from said shaft being greater than said radial distance separating said outer balancing seal from said shaft and greater than said radial distance separating said outer annular groove from said shaft, said outer peripheral edge of said second ring end being located generally radially outward of said outer annular groove and generally radially outward of said outer balancing seal and being located farther from said shaft compared to said inner and outer balancing seals;said inner balancing seal located between and exposed to said first and second fluid pressures and partitioning said first fluid pressure from said second fluid pressure, and said outer balancing seal being exposed to and retaining said first fluid pressure;said first fluid pressure acting on said annular ring and producing a first axially-oriented hydraulic force acting on said annular ring in a first hydraulic force direction toward said locating shoulder, and said first fluid pressure acting on said annular sealed region of said second ring end of said annular ring and producing a second axially-oriented hydraulic force acting on said annular ring in a second hydraulic force direction that is opposite to said first hydraulic force direction and toward said retaining shoulder;said innermost surface of said bulkhead housing being the surface of said bulkhead housing located nearest to said shaft, said innermost surface of said bulkhead housing being exposed to said second fluid pressure,a portion of said second ring end radially inward of said inner balancing seal exposed to said second fluid pressure, a portion of said second ring end radially outward of said inner balancing seal and radially inward of said outer balancing seal exposed to said first fluid pressure,a portion of said bulkhead housing radially inward of said inner balancing seal exposed to said second fluid pressure, a portion of said bulkhead housing radially outward of said inner balancing seal and radially inward of said outer balancing seal exposed to said first fluid pressure,no portion of said bulkhead housing being located directly between said first ring end of said annular ring and said retaining shoulder, and no portion of said bulkhead housing being located directly between said second ring end of said annular ring and said locating shoulder of said bulkhead housing.