Variable-displacement pump 1 delivers fluid to the left end of power cylinder 2, moving piston 3 to the right. Fluid from the right end of cylinder 2 is returned to the pump. The speed of piston 3 is varied and it is reversed by displacing the stator of pump 1. Gear pump 4 provides make-up fluid to compensate for leakage in the system. Overflow valve 5 is always open. Leakage in the system is compensated for through check valve 6 or 7, depending upon the direction of motion of piston 3. In the position shown, leakage is compensated for through valve 6, valve 7 being closed by the high pressure in the left end of cylinder 2. Upon overloads or excessive increase in pressure, valve spool 10 is shifted to the right by the opening of check valve 8 or 9, thereby connecting the delivery and suction pipelines. Consequently, if piston 3 is stopped, pump 1 operates at low pressure.
$4198$CHP,Dr$