A pressure control valve is a spring-loaded valve that is capable of maintaining a constant pressure in a system regardless of the flow rate. This is important, since most pumps e.g. gear pumps are constant-displacement types – a constant volume of fluid is pumped for each revolution of the pump shaft. If the pump were connected directly to the cylinder, it would have to start and stop each time the piston moved to a new position. Such on-off cycling reduces the lifetime of the pump and generally the machinery and is therefore undesirable.
When a pressure control valve is put into the system, the pump can remain on the whole time of the operation – when the fluid pressure exceeds the preset limit, the valve opens, and the surplus fluid is returned to the tank. In other words, when the piston is not moving, the fluid is simply circulating from the tank, through the pump, through the valve and back to the tank. If for example, the pressure control valve opens at 1010 psi, then the pressure in the lines will never get much above 1010 psi.
Related: Key Considerations in Selection of Valves
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