Relief Valve
A relief valve is the main protection element that opens when system pressure reaches the set value and sends the excess flow to tank. The setting is typically selected 10-20% above the highest load pressure the job requires. Staying open continuously turns all of the system's power into heat.
There are two basic types. In the direct acting type the spring pressure holds the spool directly; it is cheap but its opening curve is steep, and the set pressure rises as flow increases. In the pilot operated type a small pilot stage manages the main spool; the pressure stays largely independent of flow and more constant.
- Setting method: done with the oil at operating temperature, with a gauge fitted and the actuator held at end of stroke.
- Over-setting: raising the pressure increases force but strains the limits of the pump, hoses and cylinder.
- Symptom: a valve staying continuously open shows itself with a high pitched whistle and rapid oil heating.
The electronic remote control neither reads nor changes this setting. When you open the lever fully, the ceiling of the force reachable is still determined by the relief valve; if force is not enough the solution is not in the remote control settings but in the pressure setting on the hydraulic side, and that change must stay within the machine's limits.
Where this term is used: How Are Manual Hydraulic Levers Controlled Remotely? A Comparison of 6 Methods