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The present invention comprises a hydraulic tensioner for applying tension to a chain without external fluid pressure supply. The hydraulic tensioner includes a piston assembly comprising a piston with a hollow interior and a piston bore surrounding the piston. An end of the piston assembly is subme

The present invention comprises a hydraulic tensioner for applying tension to a chain without external fluid pressure supply. The hydraulic tensioner includes a piston assembly comprising a piston with a hollow interior and a piston bore surrounding the piston. An end of the piston assembly is submerged in fluid. An inlet check valve, which controls an entry of fluid into the piston, is located below the fluid level. An outlet check valve, located at an opposite end of the piston assembly from the inlet check valve, controls an exit of fluid from the piston. A non-return mechanism is coupled to the piston such that the piston extends but does not retract more than an included backlash amount. Utilizing the motion allowed within this backlash amount, the tensioner acts as a self-priming pump.

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1. A hydraulic tensioner for applying tension to a chain without external fluid pressure supply, comprising:a) a piston assembly comprising: i) a piston (31) with a hollow interior and an insert (42) surrounding the piston (31); ii) an inlet check valve (52) for controlling an entry of fluid into th

1. A hydraulic tensioner for applying tension to a chain without external fluid pressure supply, comprising:a) a piston assembly comprising: i) a piston (31) with a hollow interior and an insert (42) surrounding the piston (31); ii) an inlet check valve (52) for controlling an entry of fluid into the piston, located such that when an end of the piston assembly is submerged in fluid, the inlet check valve permits fluid flow into the hollow interior; and iii) an outlet check valve (50) for preventing air entry when the piston extends and permitting controlled fluid outflow when the piston retracts, located at an opposite end of the piston assembly from the inlet check valve (52); b) a non-return mechanism coupled to the piston (31) such that the piston (31) extends but does not retract more than an included backlash (55) amount; and c) an inlet passageway (54) from the interior to the exterior of the piston (31), wherein the inlet passageway (54) is connected to the inlet check valve; wherein the tensioner is mounted such that the inlet passageway is located below the fluid level when the end of the piston assembly is submerged in fluid; and wherein the tensioner lifts fluid into the tensioner due to piston motion within the included backlash amount, action of the inlet check valve, and action of the outlet check valve, to fill an interior of the tensioner without an external fluid pressure supply. 2. The tensioner of claim 1, wherein the non-return mechanism comprises:a) a plurality of ratchet teeth (46) formed along a length of the piston (31); and b) a pawl (45) disposed adjacent to the piston (31), wherein the pawl (45) comprises a plurality of ratchet teeth which engage the ratchet teeth (46) on the piston (31). 3. The tensioner of claim 1, further comprising an outlet passageway (56) from the interior to the exterior of the piston (31), wherein the outlet passageway is connected to the outlet check valve.4. The tensioner of claim 3, wherein the outlet passageway (56) is shaped such that the tensioner acts as a hydraulic tensioner with damping.5. The tensioner of claim 3, wherein the outlet passageway comprises an orifice (51), which restricts the outlet passageway.6. The tensioner of claim 3 wherein the outlet passageway comprises a tortuous path, which restricts the outlet passageway.7. The tensioner of claim 1, further comprising a tensioner arm (32) having a chain side (37) that contacts a chain (36) to be tensioned, wherein the hydraulic tensioner is disposed in the tensioner arm.8. The tensioner of claim 7, further comprising a stationary abutment (33) which contacts an extended end of the piston (31) such that the tensioner arm (32) is pushed away from the stationary abutment (33) and into a path of the chain (36).9. The tensioner of claim 1, wherein the inlet check valve (52) is located in the piston (31) and the outlet check valve (50) is located in the insert (42).10. The tensioner of claim 1, wherein the inlet check valve (52) is located in the insert (42) and the outlet check valve (50) is located in the piston (31).11. The tensioner of claim 1, wherein the inlet check valve is an umbrella check valve (60).12. The tensioner of claim 1, wherein the inlet check valve is a ball check valve (66).13. The tensioner of claim 1, wherein the outlet check valve comprises a ball check valve (66).14. The tensioner of claim 1, wherein, when the end of the piston assembly is submerged in fluid, the inlet check valve is located below the fluid level.15. A method of applying tension to a chain without external fluid pressure supply, comprising the steps of:a) providing a tensioner comprising: i) a piston assembly comprising: A) a piston (31) with a hollow interior and an insert (42) surrounding the piston (31); B) an inlet check valve (52) for controlling an entry of fluid into the piston, located such that when an end of the piston assembly is submerged in fluid, the inlet check valve permits fluid flow into the hollow interior; and C) an outlet check valve (50) for preventing air entry when the piston extends and permitting controlled fluid outflow when the piston retracts, located at an opposite end of the piston assembly from the inlet check valve (52); and ii) a non-return mechanism coupled to the piston (31) such that the piston (31) extends but does not retract more than an included backlash (55) amount; b) submerging an inlet end of the tensioner in a fluid supply such that an inlet passageway is under a level of the fluid supply; c) self-priming the tensioner, wherein the tensioner lifts the fluid supply into the tensioner due to piston motion within the included backlash amount, action of the inlet check valve, and action of the outlet check valve, to fill an interior of the tensioner without an external fluid pressure supply.