Combined function control valve for constant displacement pump circuit - has pressure balancing spool for motor load control sliding inside low pressure relief spool for idle running

摘要

A hydraulic valve (10) combines the three functions of pressure relief for idle running, circuit pressure limitation, and pressure regulation under load in a circuit for driving a motor (11) with a constant displacement pump (47). A differential pressure spool (22) with seating surface (29) and pressure surfaces (37) slides inside a second differential spool (19) with a seating surface (29) and pressure surface (38). The tail shaft (32) of the inner spool passes through a separating gland (33) into a chamber (23) housing a spring (24). The tail shaft end (39) is equal in area to the other pressure surface (37), so that the inner spool and spring form a pressure balance system. At the idle running or rest position (42) of the multi-way control valve (41), the outer spool (19) can lift off its seating at a low pump pressure, directing the total oil flow back to the sump (48). At a load position (51, 52) of the valve (41), the inner spool (22) is moved off its seating by pressure difference to allow proportional oil flow to the motor whilst the outer spool (19) is held against its seating. ADVANTAGE - Only two chambers and one spring are required. Easy to produce.