Direct Acting Pressure Relief Valves

Component Related Documentation

Direct-acting pressure relief valves are used to limit the maximum pressure in a hydraulic system or in a branch circuit of a system. They incorporate a knob or a hex head attached to an adjustment plunger that increases the spring tension acting against a poppet or spool, closing the flow path from the inlet port of the valve to tank. Increasing the spring tension will increase the opening pressure of the valve. When the hydraulic force acting directly on the end of the spool or poppet opposite the spring end of the spool or poppet exceeds the spring force acting to close the spool or poppet, the valve will open creating a pathway for the pressurized fluid to flow to tank, thus limiting the pressure in the circuit.

Safety Related Notes

Before working on this machine, perform lockout-tagout procedures per the rules of your plant. Determine the sources of energy on this machine – electrical, pneumatic and hydraulic – and release or vent sources of stored energy – electrical capacitors, air receivers, and hydraulic accumulators. Shut off sources of power – electrical, pneumatic and hydraulic. Safely block mechanical sources of energy such as loaded springs and loaded machine members, or safely position the machine members so they are unloaded and springs are not under tension. Beware of hot hydraulic fluid and hot surfaces which can cause burns. Never “crack a hydraulic or pneumatic fitting” to check for the presence of stored energy. Hydraulic fluid injection injuries, as well as injection injuries from many other fluids, are extremely serious and must be treated immediately by medical personnel familiar with this type of injury. Loss of body parts or death may result from improperly treated fluid injection injuries! Never use your hands to feel for a hydraulic leak! Review the schematics and think before proceeding to work on the machine to ensure you have made the machine safe to work on.