What Are The Applications Of Rubber O-rings In Safety Valves

What are the applications of rubber O-rings in safety valves

Safety valves are indispensable safety accessories for various types of boilers, pressure vessels and pressure pipelines. They are widely used in various fields such as petroleum, chemical industry, power stations, metallurgy, nuclear power, and national defense. The seals of various parts of the safety valve are divided into metal seals and non-metallic seals according to the contact type. O-ring rubber seals (hereinafter referred to as O-rings) belong to the typical structure of non-metallic seals. Rubber is an elastic polymer material, which can produce greater deformation when given a small stress. This deformation can provide contact pressure, compensate for leakage gaps, and achieve the purpose of sealing. Therefore, rubber seals are easier to achieve than other forms of sealing. , And the sealing performance is excellent, whether it is used for static sealing or dynamic sealing, the leakage rate can be kept to a small extent. Especially for dynamic seals, the frictional resistance of O-rings is very small, which can be adapted to pressure alternating occasions.

2. Applicable working conditions

The safety valve is a safety protection valve that automatically opens and closes according to the working pressure of the system. According to the principle of action, it can be divided into direct-acting and indirect-acting, spring-loaded safety valves (see Figure 1) and pilot-operated safety valves respectively. Is the representative of these two forms. Take these two commonly used safety valves as examples to illustrate the main applications of O-rings.

(1) Low pressure conditions

The safety valve is an automatic valve that does not rely on external driving force to seal (except for safety valves with auxiliary devices). The sealing load at the valve seat is mainly determined by the spring preload (spring direct load safety valve) or the working medium. Pressure (pilot-operated safety valve) is provided, the sealing load is smaller than other types of valves, and sealing is more difficult. When the set pressure is low, the spring preload or the pressure of the working medium is correspondingly small, the valve seat sealing load is small, and other types of sealing forms are difficult to seal.

(2) Dynamic sealing conditions

The pilot-operated safety valve is composed of a main valve and a pilot valve. The opening and closing of the main valve is controlled by the pressure of the pilot valve sensing system. The internal structure of the pilot valve is compact, the flow path is narrow, the space is limited, there are many relative moving parts, and the sealing part is tight. There is a piston structure between the main valve disc and the guide sleeve, in order to ensure that the medium formed by the disc and the guide sleeve does not leak out, and at the same time, the disc has good movement characteristics when the safety valve is opened.

(3) Conditions requiring strict leakage rate

Compared with non-metallic sealed structures, metal sealed structures have a higher leakage rate. According to API 527, the maximum allowable leakage rate of metal-sealed safety valve seat depends on the flow channel area and the set pressure, and the number of bubbles is 20-100/min. However, for safety valves with non-metallic seal structures, the leakage of bubbles can be as low as 0/min. Obviously, the non-metallic sealing structure is more suitable for occasions with strict requirements on leakage rate. For example, hydrogen gas is a small molecule gas, easy to escape, flammable and explosive, and very dangerous. In non-metallic sealing, the sealing structure of O-rings is relatively simple and easy to install, maintain and replace. Therefore, a large number of O-rings are used for sealing at the valve seat under hydrogen-containing conditions.

3. Main sealing form and structural design

O-rings are squeeze type seals. The basic working principle of squeeze type seals is to rely on the elastic deformation of the seal to cause contact pressure on the sealing contact surface. If the contact pressure is greater than the internal pressure of the sealed medium, no leakage will occur. A leak occurs. In order to ensure the formation of an effective seal, the performance of the material and the design of the sealing structure are very important. For different types of sealing structures, the compression amount and groove design of the O-ring are different. The sealing forms of O-rings in safety valves mainly include end face static seal, reciprocating seal and valve seat seal.