SEQUENCE VALVE AND PRESSURE REDUCING 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.

• Hydraulic sequence valve
• Pressure Reducing Valve

Let us first look the 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.

Also look causes of hydraulic system overheating and cost of hydraulic oil leaks

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.

 
Image courtesy: Google

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