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Butterfly Valve Actuation

Butterfly Valve Actuation

Feb 10,2023

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What Are the Factors That Affect the Sealing Performance of the Valve

1. Quality of valve sealing surface

When the specific pressure on the valve sealing surface is below 40MPa, the quality of the sealing surface plays a decisive role in the working sealing performance of the valve. This is because when the specific pressure on the sealing surface is small and the surface roughness is low, the amount of leakage increases rapidly. When the specific pressure on the sealing surface is large, the effect of surface roughness on the leakage is significantly reduced.

2. Width of valve sealing surface

The width of the sealing surface determines the length of the capillary hole. When the width increases, the movement stroke of the valve working fluid along the capillary hole is lengthened, thus increasing the movement resistance. Enlarging the width of the sealing surface can reduce erosion and wear in the high-pressure valve. After the width of the valve sealing surface is enlarged, it will cause the leakage stroke length to increase proportionally, so the leakage can be reduced proportionally. However, as the width of the sealing surface increases, under the same sealing force, the specific pressure of the seal decreases, which will increase the possibility of leakage. Therefore, the width of the valve sealing surface cannot be increased indefinitely.

3. The pressure difference between the front and the back of the valve when the valve is working

From a theoretical analysis, when the valves in industry are working, the pressure difference between the front and the back of the valve is proportional to the leakage. But experiments have proved that under other conditions the same, the increase in leakage exceeds the increase in pressure difference.

4. Valve sealing surface material and processing status

The material of the valve sealing surface and its treatment status have a great influence on the leakage. Since the size of the remaining gap between the sealing surfaces depends on the microscopic unevenness of the sealing surface, if the valve sealing ring made of steel material is used to cause the same degree of sealing, it must have a larger specific pressure, and its value must exceed the specific pressure value of the seal ring made of brass.

5. The nature of the valve medium

The hydrophilicity of the surface affects the amount of leakage due to the effect of the pore characteristics. When there is only a thin oil film on the valve sealing surface, the pressure of the water passing through the gap needs to be increased. Because the metal surface has good hydrophilicity, kerosene can easily penetrate the gap between the casting and the sealing connection. Therefore, in some of the most critical occasions, kerosene is used for sealing hydraulic tests. The method of filling the cavity with kerosene is used for the sealing test, which is approximately equivalent to the hydraulic sealing test under the pressure of 0.3MPa-0.4MPa.

6. The existence of the valve sealing oil film

The existence of a sealing oil film between the sealing surfaces of the valve has a significant impact on its sealing performance. When there is a sealing oil film on the surface, the hydrophilicity between the contact surfaces is destroyed, so that a large pressure difference is required to allow the medium to pass through the capillary pores. In addition, the thick sealing oil film on the surface can block the passage of the medium and improve the sealing performance of the connection.

When using oil film seals, you should pay attention: when the oil film is reduced during work, the thickness of the oil film should be restored. The grease used in the valve should not be dissolved in the medium, and should not evaporate, harden or have other chemical reactions.

7. The influence of rigidity and structure of valve closing parts

Because the closing part of the closed-circuit valve is not absolutely rigid, but has a certain degree of elasticity, the size of the valve changes under the action of the pressure related to the medium, which also causes the change of the interaction of the sealing surface force. In order to compensate for the influence of these changes on the sealing performance of the closure, it is best to make the sealing surface less rigid, that is, the elastic deformation is as large as possible.

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