Main causes of valve leakage

Valve leakage is divided into internal leakage and external leakage, internal leakage mainly affects the function of the valve, leakage will not only cause the loss of media, but also on the surrounding equipment and personnel constitute a hidden danger of accidents, pollution of the environment, a great impact.

There are two main parts of valve leakage, one is the valve body and cover flange leakage, one is the leakage of packing.

The valve body and bonnet connecting flange are sealed by fastening bolts to press gaskets. The causes of leakage are as follows:

* Stress relaxation of bolts due to thermal shock, resulting in insufficient preload of bolts; or uneven screw of bolts.

* Gasket hardness higher than flange, or aging failure or mechanical vibration caused by gasket and flange joint contact is not strict.

• low contact surface accuracy (grooves, chipping, etc.) and corrosion by medium or leakage.

* The gasket deflection and excessive partial pre-tightening during assembly exceeded the design limit of gasket, resulting in insufficient local sealing pressure.

Treatment: If the site does not have demolition conditions, can loosen the valve body and cover flange all bolts, re-uniform symmetrical fastening bolts. During overhaul, the valve is disintegrated, the sealing gasket is replaced, the valve is reassembled, and the bolt is tightened symmetrically and uniformly according to the prescribed preload force.

The pre-tightening force of bolt should be calculated in valve design, and the range of pre-tightening torque of bolt should be given on the drawing. The pre-tightening force of bolt should be controlled by torque wrench in valve assembly, and the pre-tightening force should be applied symmetrically and uniformly. Replace sealing gasket periodically. Improve the machining accuracy of the sealing surface. The design adopts multiple seals to prevent leakage.

Valve body and cover connection is internal pressure self-sealing structure, high temperature and high pressure valves generally use this sealing structure, this structure has good sealing performance, temperature and pressure changes can be good sealing, the middle flange does not withstand the pressure of working media and compact structure. There are several reasons for leakage: insufficient pre-tightening force; damage to sealing ring and self-pressure sealing parts; valve body cavity deformation.

Processing: If leakage occurs at low pressure and does not occur at high pressure, it may be due to insufficient pre-tightening of the bolts. Release all bolts and tighten them symmetrically. If the leakage occurs at low pressure and high pressure, it may be scratched at the sealing ring and the self-pressure sealing part, or the valve body cavity deformation. Remove the valve, check the self-sealing part of the valve body and the sealing ring, if the valve body self-sealing part is damaged, need to carry out grinding repair, such as the valve body self-sealing part is not damaged, but the sealing ring is damaged, replace the sealing ring, re-assembly.

Valve design to low-pressure sealing bolt pre-tightening force needed to be calculated, there should be sufficient pre-tightening force, under the pre-tightening force, the sealing ring elastic-plastic deformation, sealing the valve cavity. Reduce the number of dismantling rings. Because under the action of test pressure or high temperature and high pressure working medium, the sealing ring has plastic deformation, each time disassembly, self-pressure sealing ring and valve body self-pressure sealing parts have varying degrees of scratches on the surface, affecting the sealing. Odd high valve www.shqgfm.com