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A hydraulically driven reciprocating pump. In some embodiments, the pump includes a housing including a hydraulic chamber, a cylinder coupled to the housing, a piston assembly adapted for reciprocal motion within the housing and the cylinder, the piston assembly separating the hydraulic chamber into

A hydraulically driven reciprocating pump. In some embodiments, the pump includes a housing including a hydraulic chamber, a cylinder coupled to the housing, a piston assembly adapted for reciprocal motion within the housing and the cylinder, the piston assembly separating the hydraulic chamber into three subchambers, and a hydraulic system fluidicly coupled to each of the subchambers. The hydraulic system is actuatable to deliver hydraulic fluid to a first of the subchambers, whereby the piston assembly strokes back and a working fluid is drawn into the cylinder, to deliver hydraulic fluid to a second of the subchambers, whereby the piston assembly strokes out and the working fluid is exhausted from the cylinder, and to adjust a volume of hydraulic fluid within a third of the subchambers, whereby the piston assembly translates to bring a pressure of the working fluid in the cylinder to within a pre-selected range.

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1. A pump comprising: a housing having a hydraulic chamber;a first piston in the hydraulic chamber;a second piston separating the hydraulic chamber into at least a first subchamber and a second subchamber, and disposed for reciprocal motion within the housing;the first piston defining a third subcha

1. A pump comprising: a housing having a hydraulic chamber;a first piston in the hydraulic chamber;a second piston separating the hydraulic chamber into at least a first subchamber and a second subchamber, and disposed for reciprocal motion within the housing;the first piston defining a third subchamber in the hydraulic chamber, wherein the first piston is movable relative to the second piston;a hydraulic system fluidicly coupled with the first subchamber, the second subchamber, and the third subchamber, the hydraulic system actuatable to: deliver hydraulic fluid to the second subchamber, whereby the second subchamber is pressurized and the second piston translates in a first direction from a stroked back position toward a stroked out position;deliver hydraulic fluid to the first subchamber, whereby the first subchamber is pressurized and the second piston translates in a second direction opposite the first direction from the stroked out position toward the stroked back position; anddeliver hydraulic fluid to the third subchamber to move the first piston relative to the second piston;wherein the first piston, the second piston, the first subchamber, the second subchamber, and the third subchamber are aligned along a same central axis. 2. The pump of claim 1, wherein the second piston is in sealing engagement with an inner surface of the housing. 3. The pump of claim 1, further comprising a control system operable to actuate the hydraulic system to pressurize the second subchamber when the second piston is in the stroked back position and to pressurize the first subchamber when the second piston is in the stroked out position, whereby the second piston reciprocates within the housing. 4. The pump of claim 3, further comprising a cylinder coupled to the housing and wherein the second piston is disposed partially within the cylinder and partially within the housing, the second piston drawing a working fluid into the cylinder when translating in the second direction and exhausting the working fluid from the cylinder when translating in the first direction. 5. The pump of claim 4, further comprising means for detecting an axial position of the second piston, a first pressure sensor operable to sense a pressure of hydraulic fluid in the first subchamber, a second pressure sensor operable to sense a pressure of hydraulic fluid in the second subchamber, and a third pressure sensor operable to sense a pressure of the working fluid exhausted from the cylinder; and wherein the control system is operable to determine when the second piston is in either of the stroked out and stroked back positions as a function of the axial position of the second piston and at least one of the first pressure, the second pressure, and the third pressure. 6. The pump of claim 5, wherein said means for detecting is one of a linear displacement transducer coupled to the second piston and a resistive coil embedded in the housing, the coil having a resistance that changes in response to an applied pressure load. 7. The pump of claim 5, wherein the hydraulic system is actuatable to add hydraulic fluid to the third subchamber when the third pressure is below a pre-selected minimum value, whereby the second piston translates in the first direction, and to relieve hydraulic fluid from the third subchamber when the third pressure exceeds a pre-selected maximum value, whereby the second piston translates in the second direction. 8. A pump comprising: a housing including a hydraulic chamber;a cylinder coupled to the housing;a first piston in the hydraulic chamber;a second piston adapted for reciprocal motion within the housing and the cylinder, the second piston separating the hydraulic chamber into a first subchamber and a second subchamber;the first piston adapted for reciprocal motion within the housing and relative to the second piston, the first piston forming a third subchamber within the hydraulic chamber;a hydraulic system fluidicly coupled to each of the subchambers, the hydraulic system including an electronic control system and a valve system coupled to the electronic control system;wherein the hydraulic system is actuatable to:deliver hydraulic fluid to the first subchamber, whereby the second piston strokes back to a first position and a working fluid is drawn into the cylinder;deliver hydraulic fluid to the second subchamber, whereby the second piston strokes out to a second position and the working fluid is exhausted from the cylinder; andcontrol a volume of hydraulic fluid within the third subchamber wherein the control system electrically controls the valve system to at least three valve positions: a first valve position which seals the first subchamber from entry or exit of hydraulic fluid, a second valve position which enables the addition of hydraulic fluid from a supply network, and a third valve position which enables relief of hydraulic fluid to a return network;wherein the volume of hydraulic fluid within the third subchamber is controlled at any time when the second piston is at or between the first and second positions, whereby the second piston translates to bring a pressure of the working fluid in the cylinder to within a pre-selected range. 9. The pump of claim 8, wherein the second piston comprises a piston body, the piston body further including a flange; and wherein the first piston comprises a recess configured to receive the flange therein, the flange and the first piston translatable relative to each other. 10. The pump of claim 9, wherein the first piston further comprises a throughbore and a plurality of circumferentially spaced grooves formed in a surface bounding the throughbore, each groove enabling fluid communication between the throughbore and third second subchamber when the flange is seated within the recess of the first piston. 11. The pump of claim 9, wherein the flange comprises a frustoconical outer surface and the first piston comprises a frustoconical outer surface. 12. The pump of claim 8, further comprising a pressure sensor operable to sense a pressure of the working fluid exhausted from the cylinder and wherein the hydraulic system is actuatable to add hydraulic fluid to the third subchamber when the pressure is below a pre-selected minimum value, whereby the second piston strokes out, and actuatable to relieve hydraulic fluid from the third subchamber when the third pressure exceeds a pre-selected maximum value, whereby the second piston strokes back. 13. The pump of claim 8, wherein the housing comprises a tubular member having a wire coil therein, the coil having a resistance that changes in response to an applied pressure load. 14. The pump of claim 8: wherein the second piston comprises: a piston body translatable relative to the housing; anda bladder coupled between the piston body and the housing, the bladder separating the first subchamber and the second subchamber; andwherein the hydraulic system is actuatable to: deliver hydraulic fluid to the first subchamber, whereby the bladder flexes and the piston body translates in a first direction toward the first position; anddeliver hydraulic fluid to the second subchamber, whereby the bladder flexes and the piston body translates in a second direction toward the second position. 15. The pump of claim 14, wherein the first piston comprises a piston cover at least partially disposed within the housing, the piston cover translatable relative to the housing and relative to the piston body and having a bore configured to receive an end of the piston body. 16. The pump of claim 15, wherein the piston cover further comprises a flange aligning the bore with the end of the piston body and having a plurality of circumferentially spaced throughbores enabling hydraulic fluid to pass therethrough. 17. The pump of claim 15, wherein the first piston further comprises a bladder coupled between the piston cover and the housing, the bladder separating the second subchamber from the third subchamber. 18. The pump of claim 17, wherein each of the bladders comprises an inner layer disposed between two outer layers, the inner layer comprising a material that is more compliant than at least one of the outer layers to lubricate relative motion between the outer layers. 19. The pump of claim 17, further comprising a cylinder coupled to the housing and wherein the second piston is translatably disposed within the cylinder, the second piston drawing a working fluid into the cylinder when translating in the first direction and exhausting the working fluid from the cylinder when translating in the second direction. 20. The pump of claim 19, wherein the hydraulic system is fluidicly coupled to the third subchamber and actuatable to adjust a volume of hydraulic fluid within the third subchamber, whereby a pressure of the working fluid exhausted from the cylinder is maintained within a pre-selected range. 21. The pump of claim 14, wherein the bladder extends between a circumferential outer surface of the piston body and an circumferential inner surface of the housing. 22. A pump comprising: a housing;a piston assembly separating the hydraulic chamber into at least a first subchamber and a second subchamber, the piston assembly comprising a piston body translatable relative to the housing;a piston cover at least partially disposed within the housing, the piston cover translatable relative to the housing and relative to the piston body and configured to receive an end of the piston body during operation of the pump;a piston extending between the piston cover and the housing, the piston and the piston cover separating the second subchamber from a third subchamber; anda hydraulic system fluidicly coupled to the first subchamber and the second subchamber, the hydraulic system actuatable to: deliver hydraulic fluid to the second subchamber, whereby the second subchamber is pressurized and the piston body translates in a first direction from a stroked back position toward a stroked out position;deliver hydraulic fluid to the first subchamber, whereby the first subchamber is pressurized and the piston body translates in a second direction opposite the first direction from the stroked out position toward the stroked back position. 23. The pump of claim 22, wherein the hydraulic system is actuatable to adjust a volume of hydraulic fluid within the third subchamber to move the piston cover relative to the piston body. 24. The pump of claim 22, wherein the piston cover further comprises a bore configured to receive an end of the piston body and a flange aligning the bore with the end of the piston body and having a plurality of circumferentially spaced throughbores enabling hydraulic fluid to pass therethrough. 25. The pump of claim 24, further comprising: a fourth subchamber defined between the bore of the piston cover and the end of the piston body; anda flow restrictor disposed between the fourth subchamber and the second subchamber. 26. The pump of claim 25, wherein the flow restrictor includes an annular space between an inner surface of the bore and an outer surface of the piston body.