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Saturday, 19 September 2015

DIFFERENCE BETWEEN PRESSURE REDUCING VALVE AND PRESSURE RELIEF VALVE

We have discussed in previous post about causes of hydraulic system overheating and cost of hydraulic oil leaks as well as we have also studied various "Reasons of hydraulic hose failure".

Today we will see two, quite important, types of valves used in hydraulic system.
  • Pressure Relief valve
  • Pressure Reducing Valve
Actually you will be thinking that why I need to describe here the differences between above mentioned two types of valve?  

Suppose If I am asking to you for P RV. Which type of valve, Pressure relief valve or Pressure reducing valve, you will give me?

Actually these two types of valves are different with each other and that we will have to understand the differences between both types of valves used in hydraulic system.

First we will understand the pressure relief valve

Pressure relief valve will normally be fitted with the main hydraulic pump discharge line and the main objective of pressure relief valve is to monitor the hydraulic pressure in hydraulic pump discharge line. According to requirement of pressure to operate the actuator, we set pressure at relief valve. 

When pressure value required by the actuator increases and reaches the setting value of pressure relief valve, then pressure relief valve will come in line and permit oil to flow to reservoir and hence pressure relief valve is used in hydraulic circuit for protecting the various components of hydraulic system.

  • Pressure relief valve will normally be in closed position and it will only come in line once pressure requirement increases and reaches the setting point of relief valve.
  • Pressure relief valve will have one pilot line to sense the inlet pressure.
  • Pressure relief valve will be internally drained as the outlet of relief valve will be connected with reservoir. 

Pressure reducing valve

Pressure reducing valve will normally be fitted close with a component where we need to reduce the pressure from higher system pressure. We can see the application of pressure reducing valve in clamping and punching operation, where clamping cylinder and punching cylinder both might be operated with same hydraulic pump. 

Clamping cylinder will require lower pressure for clamping the work piece as higher pressure will damage the work piece but punching cylinder will need quite higher pressure as compared to that of clamping cylinder pressure requirement. 

Now we may use pressure reducing valve here to reduce the pressure as required by clamping cylinder.


  • Pressure reducing valve will receive higher pressure at inlet but it will deliver the pressure, as per outlet pressure setting, on its outlet.
  • Pressure reducing valve will normally be in open position.
  • Pressure reducing valve will have one check valve to allow free flow in reverse direction.
  • Pressure reducing valve will be externally drained as the outlet of such valve will not be connected with reservoir so such valve could not be internally drained.
  • Pressure reducing valve will have a separate drain line directly from valve to reservoir.
  • Pressure reducing valve will have one pilot line to sense the outlet pressure.

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