Saturday, 5 March 2016

PRESSURE RELIEF VALVE WORKING PRINCIPLE AND ITS INTERNAL CONSTRUCTION

PRESSURE RELIEF VALVE WORKING PRINCIPLE AND ITS INTERNAL CONSTRUCTION

We have discussed various hydraulic concepts in our previous post e.g. Principle of hydraulics and hydraulic system for beginners. Today we will see here the concept and internal construction of pressure relief valve. 

 
Pressure relief valves are the quite common valves used in hydraulic industries for performing two important functions as mentioned here.
  1. Protection against overload for various circuit components
  2. Limiting the force or torque applied by actuators.

Pressure relief valve: Simple type

Pressure relief valve will have two sections i.e. Body section and pilot valve section. Body section of relief valve will have a piston which will be retained to its position or seat due to the action of spring force. Pilot valve section will control the piston movement with the help of hydraulic force.

We can see one simple type of pressure relief valve in following figure. One port of pressure relief valve will be connected with pump delivery line or pressure line and other port will be connected with hydraulic reservoir.
 
Poppet will be positioned to its seat due to the spring force, one adjusting screw is provided to change the setting pressure of relief valve.

If pressure at the inlet of relief valve is not enough to overcome the spring force, in that situation poppet will be remain seated over its seat and will not allow the flow of fluid through it and therefore relief valve will be closed and will not allow flow through it.

When pressure at the inlet of relief valve increases and overcomes the spring force which was adjusted with the help of pressure adjusting screw displayed at the top of relief valve, in that situation poppet will leave the seat and will permit the flow of fluid through relief valve. 

Hence, if pressure at inlet of relief valve overcomes the setting pressure of relief valve then fluid will flow to hydraulic reservoir through relief valve and therefore further increment in pressure in pressure line will be avoided.

 
When pressure at inlet of relief valve falls below the setting pressure, poppet will again positioned to its seat due to the action of spring force and relief valve will be closed and will not allow the flow through it.


Cracking pressure in relief valve operation is defined as the pressure at which relief valve first permit the flow through it. Pressure at which relief valve allows to flow the full rated capacity will be termed as valve full flow pressure.


Image courtesy: Google

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