PRESSURE RELIEF VALVE AND SEQUENCE VALVE

In our previous post, we have discussed

 "Difference between pressure reducing valve and pressure relief valve".

Today we will see the difference between two quite important, types of valves used in hydraulic system.

1. Pressure Relief valve
2. Hydraulic sequence valve

Actually you will be thinking that why I need to describe here the differences between above mentioned two types of valve?

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.

1. 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.
2. Pressure relief valve will have one pilot line to sense the inlet pressure.
3. Pressure relief valve will be internally drained as the outlet of relief valve will be connected with reservoir.

Let us see now hydraulic sequence valve 

Hydraulic sequence valve is also type of pressure control valve. Sometime we feel need, for various mechanism and operation of machines, of operation of hydraulic cylinders in a sequence. Hydraulic sequence valves will be used when we need to provide the sequence in operation of two or more than two hydraulic cylinder.

As we can see in above symbol of hydraulic sequence valve, there will be one check valve for free flow in reverse direction.

For more detail on sequence valve click "Hydraulic sequence valve operation"

Let us see few points about hydraulic sequence valve

1. Hydraulic sequence valve will normally be in closed position and it will only come in line once pressure increases and reaches the setting point of sequence valve.
2. Hydraulic sequence valve will have one pilot line to sense the inlet pressure.
3. Hydraulic sequence valve will have one check valve to allow free flow in reverse direction.
4. Hydraulic sequence 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.
5. Hydraulic sequence valve will have a separate drain line directly from valve to reservoir.
6. Hydraulic sequence valve setting pressure will be higher than the operating pressure of first actuator.

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