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Pressure Relief Schematic Symbol
Pressure Relief Valve have some variations of the schematic symbol for a direct acting relief valve. The P label is the inlet port from the pump and the Label is the port that leads back to tank.
How Pressure Relief work with Direct Acting ?
Direct acting Relief valve is the most basic of the pressure controls, consisting of only one poppet and one spring. It is used to limit maximum system pressure.
The advantages of a direct acting style are that it is:
- inexpensive
- fast-acting
- simple
This valve is good for controlling sudden, momentary pressure spikes. It can also be used as a pilot control for other valves.
How Relief Valve Work
Here is a direct acting relief valve shown in schematic form and as a graphic cutaway.
The relief pressure is set to 1000 psi and the system pressure is currently at 250 psi, so the relief valve remains closed.
“Relief Valve is the maximum system pressure that will occur under normal operating conditions and with all of the pump’s flow passing through the relief valve”
⇒ Pressure Increases Position
As the load is increased on the motor and the pressure increases, which causes the relief valve to open slightly. This is because the cracking pressure on this relief valve is 500 psi below the current setting pressure.
As system pressure approaches the relief setting so the valve opens part-way and divides flow. The motor will slow down as a result.
⇒ Open Position
As the system pressure increases from the initial cracking pressure towards the pressure setting, the relief valve will open more and more. Once the relief pressure setting is reached, the relief valve will be fully open, and diverting all the pump’s flow back to the tank. The motor will now be stopped.
⇒ Close Position
Now, as soon as system pressure falls below the pressure needed to open it, the relief valve closes again.
