What’s Safety Valve?

The safety valve plays a safety role in the valve system. When the system pressure exceeds the specified value, the safety valve opens, and a part of the gas / fluid in the system is discharged to the atmosphere / pipeline, so that the system pressure does not exceed the allowable value, thereby ensuring that the system does not cause an accident due to excessive pressure.

1. Introduction of the Safety Valve

Safety valve is a special valve that is normally closed under the action of external force. When the medium or pressure in the equipment or pipeline rises above the specified value, it is a special valve to prevent the medium or pressure in the pipeline or equipment from exceeding the specified value by discharging the medium outside the system. Safety valves belong to the category of automatic valves, which are mainly used on boilers, pressure vessels and pipelines, controlling the pressure to not exceed the specified value, it plays an important role in protecting personal safety and equipment operation. It is noted that safety valves must be pressure tested before they can be used.

2. Classification of the Safety Valve

According to its overall structure and loading mechanism, it can be divided into three types: heavy hammer-lever type, spring type and pulse type.

1) Heavy Hammer-lever Type

The heavy hammer-lever type safety valve uses a heavy hammer and a lever to balance the forces acting on the valve disc. According to the principle of leverage, it can use a heavy weight to obtain a larger force through the increase of the lever, and adjust the opening pressure of the safety valve by moving the position of the weight (or changing the weight of the weight).

The heavy hammer-lever type safety valve has a simple structure, it is easy to adjust, and is relatively accurate. The added load will not increase significantly due to the rise of the valve flap. It is suitable for high temperature applications. It is used in boilers and high temperature pressure vessels. However, the weight of the heavy hammer-lever safety valve is heavy, the loading mechanism is easy to vibrate, and often leaks due to vibration. Its seat pressure is low, and it is not easy to close and maintain tightness after opening.

2) Spring Slightly-opening Type

The spring slightly-opening safety valve uses the force of a compression spring to balance the force acting on the valve disc. The compression amount of the spiral coil spring can be adjusted by turning the adjusting nut on it. With this structure, the opening (setting) pressure of the safety valve can be corrected as required. The spring slightly-opening safety valve has a light and compact structure, high sensitivity, unlimited installation positions, and low sensitivity to vibration, so it can be used on mobile pressure vessels. The disadvantage of this type of safety valve is that the applied load will change with the opening of the valve, that is, as the valve disc rises, the compression amount of the spring increases, and the force on the valve disc also increases. This is detrimental to the rapid opening of the safety valve. In addition, the spring on the valve will reduce the spring force due to the long-term effect of high temperature. When it is used on a container with a higher temperature, it is often necessary to consider the heat insulation or heat dissipation of the spring, thereby complicating the structure. 

3) Pulse Type

The pulse type safety valve is composed of a main valve and an auxiliary valve. The action of the main valve is driven by the pulse action of the auxiliary valve, and its structure is complicated. Generally, it is only suitable for boilers and pressure vessels with large safety relief.

Among the above three types of safety valves, spring-type safety valves are more commonly used.