Analyze the reason of dynamic instability of safety valve

The dynamic instability of the safety valve is mainly caused by the following reasons: the discharge capacity of the safety valve exceeds the flow of media into the safety valve, the excessive spring stiffness, the large back pressure in the upper chamber of the disc when the valve is opened, and the external dynamic interference.

I. impact of emission capacity:

It may occur that the discharge capacity of the relief valve exceeds the media flow into the valve when:

1. When the cross-sectional area of the selected safety valve exceeds the cross-sectional area required for calculation:

2. When the safety valve is installed on the system with emergency displacement variation:

3. When the cross-sectional area of the inlet pipeline is insufficient, etc.;

Ii. Influence of spring stiffness:

Spring stiffness is too big can also be the cause of the disc oscillation. Full rev safety valve can achieve full open emissions depends on the medium to long-term, but spring stiffness is too large, the force will not be able to have a spring force to the set of open height, the relief valve can't reach the quantity of emissions, as soon as this will lead to the relief valve open return, form oscillation. If small stiffness, it would under low pressure relief valve to return. In order to eliminate this kind of phenomenon, should be installed according to design of the spring, or when the design should be more actual groups of spring test, through the test to determine the most appropriate spring.

Iii. Influence of system back pressure:

With similar impact of spring stiffness is too large, the disc above the coelomic cavity the relief valve opens when the back pressure may also cause the disc oscillation. In order to avoid to produce a large back pressure, to open the relief valve body is the use of open hole above the valve body cavity connected with the atmosphere. For the enclosed safety valve, the disc can be above the coelom export or export branch pipe connected to the valve body, use the suction effect to reduce the pressure on top of the disc