PURPOSE: To obtain stable characteristics of a pump, by providing an oil passage communicated through a throttle to a surface receiving delivery pressure of a main piston and a tank.
CONSTITUTION: An oil passage 24 opened to a surface 4' of a main piston 4 and a tank (not shown) through a throttle 12 is provided so as to relieve pressure oil in a pressure chamber 23. When a rotor 8 is rotated counter clockwise from a state for a ring 7 pressed rightward by a spring 10, pressure oil from a delivery chamber 15 is acted upon a spool 6 of a pressure compensator 3 with that from a pressure chamber 22 in a piston 5. If delivery pressure is increased, the spool 6 is moved rightward and delivery oil goes into the pressure chamber 23 from a port 17, partially passes through the throttle 12 and the oil passage 24 and is relieved to the tank, while high pressure oil by the throttle 12 acts to the surface 4' of the main piston 4 to move the ring 7 leftward. In this way, oil leaking from the main piston part is reduced to a minimum limit, thus a stable characteristic with a small change of pressure can be obtained.
DAIGO TOMIO
HIROKAWA NOBORU
