Difference Between Relief Valve and Safety Valve (With Table)

Industrial safety is an important factor in the making and processing of industrial goods. Sometimes, the machinery heats up more than its limit, which results in overpressure conditions. This further can cause damage to life, property as well as environment. In order to prevent such situations, safety devices are designed and used. They work to protect the systems and machinery from facing overpressure. Relief Valve and Safety Valve are two such safety devices.

Relief Valve vs Safety Valve

The difference between Relief Valve and Safety Valve is that Relief Valve helps in maintaining the right amount of pressure in a system so that it does not rise, whereas, Safety Valve helps in vacating excess pressure from the system when the pressure rises to a high level and is capable of causing overpressure. Both these safety devices differ in terms of their ways of treating overpressure conditions.

A Relief Valve is a device designed to protect the machinery or systems in a process industry from overpressure. The device maintains a specific level of pressure in the system. The specific level is basically known as Setpoint. If the pressure rises above the setpoint, it can lead to overpressure and cause extreme damages.

On the other hand, a Safety Valve is a device designed to prevent the accumulation of excess pressure in a system. When the pressure in the system rises beyond the setpoint, the safety valve vacates the excess pressure from it. This, in turn, prevents overpressure conditions from forming.

Comparison Table Between Relief Valve and Safety Valve

Parameters of Comparison Relief ValveSafety Valve
Definition A Relief Valve is a device that helps to maintain the pressure of a system at a specific level. A Safety Valve is a device that helps to release excess pressure when it exceeds the limit.
WorkingIt opens up in proportion with the increase in pressure level. It opens up fully and immediately as the pressure rises.
Operator It is operated with the help of an operator. While there is no operator used.
SetpointThe setpoint is 10 per cent higher than the working pressure limit. Whereas the setpoint is 3 per cent higher than the working pressure limit.
TypesThere are four types: pop-type, pilot-operated, direct-operated and internal. The types are divided based on their applications.
PurposeIt does not allow the pressure to go beyond a certain limit. While it releases excess pressure and prevents overpressure.

What is Relief Valve?

A Relief Valve or a PRV, i.e. Pressure Relief Valve, is a safety device that comes into use for maintaining the pressure of a system at a specific level so that overpressure conditions do not occur. The device does not allow the pressure to rise above the setpoint.

The relief valve tends to open up gradually with the increase in the amount of pressure. The setpoint of a relief valve is set at 10 per cent higher than the working pressure limit. When the pressure starts rising above the setpoint, the valve opens up to control it and prevent overpressure. It responds by releasing excess auxiliary passage flow from the system back to the tank for preventing system failure.

The opening of a relief valve is directly proportional to the amount of increase in pressure. It opens up only until the pressure goes back to the specified limit. An operator is used to complete this process. The process of opening the valve is gradual.

Overpressure conditions cause harm to several aspects of an industry. A relief valve is thus fitted to the system so that the pressure is maintained at the desired setpoint and there is no damage caused.

What is Safety Valve?

A Safety Valve is a safety device that is designed in a way to get activated automatically when the pressure tends to rise. The device helps to vacate excess amount of pressure from the system. This, as a result, prevents overpressure conditions.

The safety valve opens up immediately as the pressure rises above the set limit. The setpoint of a safety valve is set at 3 per cent higher than the working pressure limit. Even when the pressure rises slightly above the set limit, the valve opens up and starts releasing the excess pressure. It then goes back to its initial state after the pressure comes down to the desired limit.

Unlike the relief valve, there is no operator used in a safety valve. It opens up immediately when there is an increase in pressure level. It closes when the excess pressure is pushed out. The process of opening and closing the valve is sudden and faster.

A safety valve works as the last option for preventing overpressure conditions. It has the capability to operate anytime. The chance of damages and losses is lessened when the valve is used.

Main Differences Between Relief Valve and Safety Valve

  1. Relief Valve maintains pressure at a specific level while Safety Valve releases the excess amount of pressure.
  2. The opening of the relief valve is gradual, whereas the safety valve opens up immediately.
  3. There is no operator in the safety valve while the relief valve has one.
  4. Setpoints of relief and safety valve are 10 per cent and 3 per cent higher than the limit, respectively.
  5. The safety valve has many types, while the relief valve has only three.

Conclusion

The industrial environment brings with it the risk of damage to life and property. The systems or machinery used for working need to be taken proper care of so that no unavoidable situations arise. Therefore, various types of safety devices are introduced to help in the process.

Relief valve and Safety valve are two of the most commonly used safety devices that take care of overpressure conditions. The relief valve maintains the systemic pressure at a specified limit, and the safety valve releases the excess amount of pressure.

Both these devices prevent damages due to overpressure conditions. Although they are used for the same purpose, their working ways are quite different. The relief valve uses an operator while there is no operator in the safety valve. The opening and closing process of the safety valve is faster and sudden in comparison.

References

  1. https://www.researchgate.net/profile/Daniel_Pierrat/publication/229045381_Vibration_and_chattering_of_conventional_safety_relief_valve_under_built_up_back_pressure/links/568e97d008aeaa1481b02b1d.pdf
  2. https://www.sciencedirect.com/science/article/pii/S0895717711003955