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Knowing that the valve knows that when the pressure in the protected system rises, an additional force acting on the sensing element is generated, causing the element to move to open the gap in the safety valve passage, and the medium is discharged through the gap.
The discharge capacity of the safety valve and the service life of its parts are related to the dynamic stability of the safety valve. The oscillation of the valve flap will reduce the passage cross-sectional area and discharge capacity of the safety valve, and the valve seat and the seat height and the opening height limit. The collision of the positioner will damage the sealing surface of the safety valve and other parts. The two-stage full-open safety valve is most prone to flap oscillation.
The dynamic instability of the safety valve is mainly caused by the following reasons: the discharge capacity of the safety valve exceeds the flow rate of the medium entering the safety valve, the spring stiffness is too large, and the large back pressure and the outside of the valve cavity occur when the valve is opened. Dynamic interference.
I. Impact of emission capacity
The discharge capacity of the safety valve may exceed the flow rate of the medium entering the valve in the following cases: 1. When the channel cross-sectional area of ​​the selected safety valve exceeds the cross-sectional area required for calculation: 2. When the safety valve is installed in emergency displacement On a system with changes: 3. When the cross-sectional area of ​​the inlet pipe is not enough, etc.
Second, the effect of spring stiffness
Excessive spring stiffness can also be the cause of valve flap oscillation. The full-open safety valve can achieve full opening discharge depending on the medium recoil, but when the spring stiffness is too large, this force can not be used to set the spring force. The opening height, so the safety valve can not reach the full amount of discharge, this will cause the safety valve to return to the seat as soon as it opens, forming an oscillation. If the stiffness is small, the safety valve will return to the seat under a very low pressure. In order to eliminate this Phenomenon, should be installed with the design of the spring, or in the design should be more practical sets of springs to test, through testing to determine the most suitable spring.
Third, the system back pressure effect:
Similar to the effect of excessive spring stiffness, the back pressure generated by the body cavity above the valve when the safety valve is opened may also cause the valve flap to oscillate. To avoid large back pressure, the open safety valve is utilized on the valve body. The opening allows the body cavity above the valve flap to communicate with the atmosphere. For the enclosed safety valve, the body cavity above the valve flap can be connected to the valve body outlet or the outlet branch pipe, and the suction effect generated by the valve can be used to reduce the pressure above the valve flap.
A vertical valve safety valve: http://?20_2.html
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