Double acting hydraulic jack with an end of stroke device

摘要

A double-acting hydraulic jack has a cylinder, a piston dividing the cylinder into first and second chambers of variable volume on opposite sides of the piston, and a piston rod with first and second passages opening into the first and second chambers respectively. The piston is moved by supply of pressurized fluid to one passage or the other. An end-of-stroke device is provided to relieve the high pressure applied to the first chamber when the piston comes to the end of its stroke under the action of the pressure fluid supplied to that chamber through the first passage. The device comprises a bore in the piston. The axis of the bore is parallel to the piston axis. The bore contains a small moveable rod urged to project from the bore into the second chamber by high fluid pressure taken from the first passage to move a sliding sleeve in the bore. This sleeve movement is transmitted to urge the small rod and also blocks a third passage leading to the bore from the first passage. The small rod projecting into the second chamber swept by the piston is brought into abutment with an end of the cylinder causing the rod to move back into the bore. This rod movement is transmitted to the sleeve which opens the third passage through which the high pressure in the first passage is relieved via the bore and an ever open fourth passage between the bore and second chamber.