Hydraulic Pressure Relief Valve - Selecting and Setting

What does a pressure relief valve do?

A hydraulic pressure relief valve (PRV) limits system pressure to an adjustable maximum. If pressure rises because a cylinder is blocked or a line is closed, the valve opens and returns the excess flow to the tank. This keeps pressure stable and protects the system from overload.

There are two basic designs. The direct-acting PRV opens as soon as pressure exceeds the spring force on the poppet or spool - simple, fast and robust at small flows. The pilot-operated PRV uses a small pilot stage to control the main spool, giving a flat characteristic even at high pressure and large flow.

Which specifications drive the selection?

The key values are rated pressure, rated flow and the mounting style. The set pressure should sit about 10 to 15 percent above the maximum working pressure, so the valve does not trip in normal operation but opens reliably under a fault.

• Choose the rated flow so the full pump flow passes with acceptable pressure drop.
• Use direct-acting PRVs for small flows and fast response, e.g. as secondary protection.
• Use pilot-operated PRVs for high pressures and large flows with a flat characteristic.
• Match the seal material (NBR, FKM) to the hydraulic fluid and temperature range.
• Provide an adequate tank-line cross section to avoid cavitation.

How do you set a pressure relief valve correctly?

Setting is done on the running system with a pressure gauge in the pressure branch. First back the adjusting screw fully out, then with the actuator blocked tighten it slowly until the desired cracking pressure shows on the gauge. Finally lock the counter nut.

• Connect the gauge as close to the valve as possible in the pressure branch.
• Relieve the adjusting screw, start the unit, then raise slowly to the target pressure.
• Tighten the counter nut and record the value.
• Check for leaks and correct response behaviour after setting.

Frequently asked questions