What is the working principle of the safety valve?

Time：2021/9/8 15:39:14 Category：TECHNICAL ARTICLE Source： Click：

The spring safety valve must be a familiar term for many guys, but the spring safety valve does play a very important role in our lives. So what are the working principles and structural characteristics of the spring safety valve?

First, The working principle of spring safety valve

When the steam pressure under the safety valve disc exceeds the pressing force of the spring, the disc is pushed open. After the valve flap opens, the exhaust steam acts on the valve flap clamping ring due to the rebound of the lower adjusting ring, so that the valve opens quickly. As the valve flap moves up, steam impinges on the upper regulating ring, making the direction of exhaust steam tend to be vertical downward. The reaction force generated by the exhaust steam pushes the valve flap upward and keeps the valve flap within a certain pressure range. As the safety valve is opened at a sufficient lifting height, the steam is continuously discharged, and the steam pressure in the system is gradually reduced. At this time, the force of the spring will overcome the steam pressure acting on the valve flap and the reaction force of the exhaust steam, thereby closing the safety valve.

Second, the structural characteristics of the spring safety valve

1. The point of action of the stem force is reduced, and the sealing performance is improved. The point of action of the stem force of the ordinary flat disc is not only higher than the sealing surface, but also indirectly acts on the disc. For valves with flexible discs, the point of action of the stem force is reduced below the sealing surface, and it acts directly on the disc. This structural improvement greatly improves the anti-vibration ability of the valve, that is, the sealing stability is greatly improved. In other words, when the valve has the same degree of vibration, the flexible disc valve is less prone to leakage. This performance has been verified in the actual operation of the safety valve.

2. The "flexible disc" structure not only improves the operating sealing performance, but also increases the operating pressure value that maintains the tightness. For the design of ordinary flat disc, the valve will "prevent" when the operating pressure rises to the valve set pressure (ie 95% of the set pressure). For spring-loaded safety valves, the existence of "pre-bleed" is a normal phenomenon, and the existence of "pre-bleed" can help the spring-loaded safety valve to take off to a certain extent. Therefore, Crosby has set the difference between the design pressure of the spring-loaded safety valve and the maximum operating pressure to be more than 5%.

3. The "flexible disc" structure introduces system pressure into the annular groove on the back side of the disc sealing surface and acts on the annular slope opposite to the disc sealing surface. Since the sealing surface has a certain degree of elasticity, it will follow the medium in the system. As the pressure rises, the disc sealing surface is pushed down by the pressure of the system to produce a slight deformation, and it is tightly combined with the nozzle sealing surface, so that the valve pre-release point is delayed.