Causes and solutions of valve sealing surface leakage

Valve is the most used in a fluid system, a control unit can be used to switch or control flow and adjustment etc, and from the simplest truncation function, the valve seal in machinery, its function is to prevent medium, from its place, between the cavity body along parts of the combination of leak outward or block the external material into the interior, sealing effect, part of the said seal or sealing structure, referred to as "seal, the two combined with surface in contact with the seal, the sealing effect of surface is called the sealing surface.

Valve sealing surface is the core of the valve, it can be divided into the form of leakage can be generally divided into these kinds, that is, sealing surface leakage, sealing ring joint leakage, closure of the leakage and leakage between the sealing surface embedded foreign matter.Valve in the pipeline and equipment is one of the most widely used to cut off the flow of media, therefore, its sealing is the main factor in the decision of internal leakage or not.Valve sealing surface generally consists of a pair of sealing pairs, one on the body, the other on the disc. 

The reasons for the leakage of the sealing surface are generally as follows:

First, the sealing surface is ground uneven, cannot form the sealing line;

Second, the connection between the stem and the closure of the center of the suspension, deviation or wear;

Three, the valve stem bending or assembly is not straight, so that the closing parts askew or not meet the center;

Iv. Improper selection of sealing surface material or failure to select valve according to working conditions, sealing surface is prone to corrosion, erosion and wear;

5. The surfacing welding and heat treatment did not operate according to the rules, and the defects such as wear caused by low hardness, corrosion caused by burning of alloy elements, cracks caused by excessive internal stress, etc.;

Six, after surface treatment of the sealing surface peeling or due to excessive grinding, lost the original performance;

Seven, sealing surface closure is not strict or due to the closure of the cold shrinkage of the cracks, the occurrence of corrosion phenomenon;

Eight, to cut off the valve as a throttle valve, pressure reducing valve use, sealing surface is eroded and destroyed;

Nine, the valve has been to the full closed position note to apply excessive closing force, including incorrect use of long lever operation, sealing surface is crushed, squeeze deformation;

Ten, the sealing surface wear too much and the phenomenon of dropped line, that is, the sealing pair can not be well closed;

Valve sealing surface leakage prevention and elimination methods:

1. When the sealing surface is ground, the lapping tool, grinding agent, emery cloth, sandpaper and other objects should choose a reasonable grinding method to be correct. After grinding, the sealing surface should be colored and checked without indentation, crack, scratch and other defects.

Second, the connection between the stem and the closing part should meet the design requirements, the center of the head does not meet the requirements, should be repaired, the center of the head should have a certain clearance, especially the stem table shoulder and the closing part of the axial clearance is not less than 2 mm;

3, stem bending should be straightened, stem, stem nut, shutoff, seat after adjustment, they should be in a common axis;

Iv. When selecting valve or replacing sealing surface, it should meet working conditions. After processing, the sealing surface has better corrosion resistance, abrasion resistance and other properties.

5. The surfacing welding and heat treatment process shall conform to the technical requirements of the regulations and specifications. After the sealing surface is processed, it shall be checked and accepted.

Six, sealing surface surface ping fire, nitriding, infiltration shed, plating and other processes must be carried out in strict accordance with the technical requirements of its regulations and specifications, grinding sealing surface permeable layer should not exceed one third of the layer of a pair of coating and permeable layer damage serious, should get rid of coating and permeable layer after re-surface treatment.The sealing surface of high frequency broken fire can be repaired by repeated throwing fire.

Seven, the valve close or open should be marked, to close loose should be repaired in time.For high temperature valve, some of the cold shrinkage after the close of the seam, should be closed after a certain interval of time again more than once;

Eight, for the valve to cut off the valve, not allowed to be used as a throttle valve, pressure reducing valve, the closing parts should be in a fully open or fully closed position if the need to adjust the media flow and pressure, should be set up separately throttle valve and pressure reducing valve;

Nine, the valve should be opened and closed in accordance with the "valve operation" section, the valve closing force is appropriate, the diameter of the hand wheel is less than 320 mm, only one person is allowed to operate, equal to or greater than 320 mm diameter of the hand wheel, two people are allowed to operate, or one person with the help of a lever operation within 500 mm;

X. after the waterline drops, it should be adjusted, and the sealing surface that cannot be adjusted should be replaced;