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How to avoid damage to valve sealing surface

Update:09-07-2020
Summary:

The valve is a control component in the pipeline fluid […]

The valve is a control component in the pipeline fluid transportation system. It is used to change the cross-section of the passage and the direction of the medium flow. It has the functions of diversion, cut-off, throttling, check, shunt or overflow pressure relief. There are two reasons for the damage of the sealing surface: artificial damage and natural damage. Man-made damage is caused by factors such as poor design, imprecise manufacturing, improper material selection, improper installation, poor use and poor maintenance. Natural damage is the wear of the valve under normal working conditions, and the damage caused by the inevitable corrosion and erosion of the sealing surface by the medium.

 

Specifically, the main causes of valve sealing surface damage are the following:

 

1. Improper installation and poor maintenance lead to abnormal working of the sealing surface. The valve runs ill and damages the sealing surface prematurely.

 

2. Damage caused by improper selection and poor operation. The main performance is that the valve is not selected according to the working conditions, and the cut-off valve is used as a throttle valve, which results in an excessively high closing pressure and too fast or inadequate sealing, which causes erosion and wear on the sealing surface.

 

3. The processing quality of the sealing surface is not good, mainly due to defects such as cracks, pores and ballast on the sealing surface, which are caused by improper selection of surfacing and heat treatment specifications and poor handling during the surfacing and heat treatment process. Too high or too low is due to wrong material selection or improper heat treatment. The hardness of the sealing surface is uneven and not resistant to erosion, mainly because the underlying metal is blown up during the surfacing process, and the alloy composition of the sealing surface is diluted Caused by. Of course, there are also design issues.

 

 

4. Mechanical damage, the sealing surface will be damaged by scratches, bumps, crushing, etc. during opening and closing. Between the two sealing surfaces, under the action of high temperature and high pressure, atoms will penetrate into each other, causing blocking phenomenon. When the two sealing surfaces move with each other, the adhesion is easily torn. The higher the roughness of the sealing surface, the more easily this phenomenon occurs. During the closing process of the valve and the valve flap in the process of reseating, the sealing surface will be injured and crushed, causing the sealing surface to be partially worn or indented.

 

5. The erosion of the medium is the result of wear, flushing and cavitation on the sealing surface when the medium is in motion. At a certain speed, the floating fine particles in the medium interfere with the sealing surface and cause local damage. The high-speed media directly flushes the sealing surface to cause local damage. When the medium is mixed and partially vaporized, the gas-producing bubble bursts Impact on the sealing surface, causing local damage. The erosion of the medium combined with the alternating action of chemical erosion will strongly erode the sealing surface.

 

6. Electrochemical erosion, the contact between the sealing surfaces, the contact between the sealing surface and the closing body and the valve body, the concentration difference of the medium, the difference in oxygen concentration, etc., will cause a potential difference, and electrochemical erosion will occur, causing the sealing surface on the anode side to be erosion.

 

7. The chemical erosion of the medium, the medium near the sealing surface does not generate current, the medium directly plays a chemical role with the sealing surface, and erodes the sealing surface.

 

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