Two stage hydraulic relief valve - having main spool which carries spring biased pilot stage to provide damped operation

摘要

A two stage hydraulic relief valve provides damping and reduces dependence upon flow variations. The main spool carries a pilot stage spool which is spring biased against a retaining ring and the complete spool assembly is forced left wards against the inlet port in the neutral position. When the supply pressure is below the spring rate setting the pressure is the same on both sides of the spool. When the pressure exceeds the preset value the pilot spool moves rightwards and the spring side of the spool discharges flow to exhaust through the control port to outlet. The pressure then falls on the spring side of the spool and a differential force across the spool results in a movement of the main spool right wards. Pressure reduction then occurs directly from inlet to outlet over the main spool.