Pressure Relief Valve Working, Types, Parts

A pressure relief valve is a safety device that is used to protect the equipment during an overpressure event.

Now, first of all, we will understand what an over-pressure event is. An overpressure event is a condition in which, the pressure of the system get exceeds the design pressure of the system or we can say exceeds the maximum allowable working pressure(MAWP). So if the pressure of a system pressure increases beyond the maximum design pressure then the system may fail and accidents can occur which could harm the equipment and life of the operator.

Thus, to prevent this overpressure occurrence we use pressure relief valves in the system which drain the extra fluid or extra pressure directly into the tank and allow only that much pressure at which the relief valve is set.

Pressure relief valves should be operating at all times, especially during a power failure when the other system controls are not operational. If somehow a condition occurs that can cause a pressure in the system than the maximum allowable pressure then the pressure relief valve is the only device that can prevent failure in the system. So it is important to design the pressure relief valve in a way in which it is easy to get operate and should not be complicated. Let us understand this by an example.

Suppose the maximum allowed limit pressure of the system is 200 bar and the components used in the hydraulic system like cylinders are required to operate at 120 bar. So whenever there is a pressure increase of more than 120 bar in this system, the pressure relief valve will get open and drain the access amount of pressure by allowing the fluid to flow from this valve directly to the tank. So in this case, we have set the pressure of safety relief at 120 bar so whenever there is an increase of pressure above 120 bar, the pressure relief valve will get open and drain the extra fluid into the tank. Thus, the pressure remains below that particular limit with the help of a pressure relief valve.

Table of Contents

Components of Pressure Relief Valve

Inlet Nozzle
Valve Seat
Seat Holder
Valve Body
Set Pressure Adjusting Screw
Cap
Spring
Bonnet
Seal

The basic working of a Pressure Relief Valve

Now, we will understand the working of the pressure relief valve. In this case, we will take a simple relief valve and the simple spring valve has only one spring. The valve is installed in a way that one port of the valve is connected to the pressure line and another port is connected to the tank. There is a ball, body, spring, adjusting screw, and seat in the simple pressure relief valve. Normally, the ball is held at the seat by the thrust of the spring. The thrust of the spring can be adjusted by the adjusting screw.

Case 1: When the inlet pressure is insufficient to overcome the spring force, the ball remains at its seat, and the valve is closed. In this case, the flow will go into the hydraulic system.

Case 2: When the inlet pressure is enough to overcome the spring force, the ball will get lifted from its seat, and the valve gets open. In this case, the extra flow will go into the hydraulic tank. This flow will prevent the pressure increase in the pressure line. When the inlet pressure gets below the spring force, then the ball will rest at its seat and the valve will get close.

Types of Pressure Relief Valves

Direct Type Relief Valve
Pilot Operated Relief Valve
Solenoid Controlled Relief Valve

Symbol of pressure relief valve

The symbol of the pressure relief valve is as below:

Frequently Asked Questions

What is a pressure relief valve used for?

A pressure relief valve is a safety device that is used to protect the equipment during an overpressure. An overpressure event is a condition in which, the pressure of the system get exceeds the design pressure of the system or we can say exceeds the maximum allowable working pressure(MAWP).

Symbol of pressure relief valve?