Method for ensuring sealing for rigid sealing valves

January 22, 2024

The electric control valve sealing surface processing quality for the rigid sealing pair, the method of ensuring the sealing is to adhere the two sealing surfaces to each other, so that the gap between the surfaces becomes a capillary-like narrow slit, and is not more than 0.02 mm. As the medium flows through the slit, as the time increases, a "polarized molecular layer" is formed on the wall of the slit with a thickness of 0.01 mm. When the width of the slit is less than 0.02 mm of the thickness of the two layers of polarized molecules, a complete "blocking" phenomenon occurs, which prevents the passage of the medium and achieves a sealing effect.

If there is no foreign matter between the two sealing faces, the cause of the gap can only be the influence of the peak value of the sealing surface roughness and the value of the surface shape deviation. When the roughness is R=0.2um, the microscopic unevenness is 10 points and the height is R=1.25um. The corresponding surface flatness tolerance is 5th grade and the tolerance value is 8um. When the two surfaces are in contact, the total error is 18.5 um, that is, the maximum gap produced is 0.0185 mm, which is less than 0.02 mm. When the roughness r = 0.4 um, the microscopic unevenness 10 point height value r = 2.5 um, and the maximum gap generated when the two surfaces are in contact is 0.021 mm, which is larger than 0.02 mm. It can be seen from the calculation that the sealing effect can be achieved when the roughness r<=0.2 um. In fact, when the valve is in the closed state, under the action of the axial force of the valve stem, a certain specific pressure is generated on the sealing surface, so that the peak of the sealing surface is compressed, and the original gap is reduced. Under the same specific pressure, for the steel sealing surface, the roughness can be selected as r=0.2-0.4um, and the sealing surface roughness of brass can be selected as r=0.8-1.6um. Analysis shows that in order to ensure the sealing performance of the valve, the steam relief valve should be added to improve the surface roughness and flatness.

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