Anti-Shock and Port Relief Valve
A port relief valve is a local protection element that limits an instantaneous pressure spike in a single actuator line. It is usually set 20-50 bar higher than the main relief valve and opens only at the moment of a shock. It comes into play when an external force strains the cylinder.
The main relief valve protects the pump side; but when the load strains the boom from the outside, for example when the bucket hits an obstacle, a pressure spike occurs at the cylinder that the main valve cannot see. The port relief valve limits this shock directly in the actuator line.
- Anti-cavitation function: many types also have a check valve in the same body that allows oil to be drawn from tank; it fills the void formed after the shock.
- Setting logic: it must be above the main relief setting so that it never opens in normal operation.
- Symptom: a port relief valve left set too low gives the feeling that the motion "slips" under heavy load.
On an electronic remote control, shortening the ramp time or selecting a very sharp characteristic increases the shock at the start and stop moments of a motion. Instead of constantly dumping these shocks onto the port relief valve, lengthening the ramp time somewhat improves both mechanical life and operator comfort.
Where this term is used: How Are Manual Hydraulic Levers Controlled Remotely? A Comparison of 6 Methods