Five situations of valve leakage and countermeasures


no.1 Leakage at packing
The leakage of the valve, the proportion of the packing is larger

►Reason:

1. The accuracy of the valve stem is not high, and there are defects such as bending, corrosion and wear;
2. The gland, bolts, and other parts are damaged, so that the gland cannot be compressed;
3. The filler has aged and lost its elasticity after it has exceeded its service life;
4. The packing is not selected correctly, it is not resistant to the corrosion of the medium, and it is not resistant to the use of high pressure or vacuum, high temperature or low temperature of the valve;
5. The gland is skewed, and the gap between the gland and the valve stem is too small or too large, resulting in wear of the valve stem and damage to the packing.
6. The packing is installed incorrectly, and there are defects such as replacing the big with the small, the screw coil joint is bad, and the upper is tight and the lower is loose;
7. The number of packing turns is insufficient, and the gland is not pressed tightly;
8. Improper operation, excessive force, etc.;
►Maintenance method
1. The material and type of packing should be selected according to the working conditions;
2. Install the packing correctly according to the relevant regulations, the packing should be placed and pressed one by one, and the joint should be at 30℃ or 45℃;
3. The fillers that have been used for too long, aged and damaged should be replaced in time;
4. After the valve stem is bent and worn, it should be straightened and repaired, and if the damage is serious, it should be replaced in time;
5. The packing should be installed according to the specified number of turns, the gland should be tightened symmetrically and evenly, and the pressure sleeve should have a pre-tightening clearance of more than 5mm;
6. Damaged glands, bolts and other components should be repaired or replaced in time;
7. The operating procedures should be followed, except for the impact handwheel, operate at a constant speed and normal force;
8. Tighten the gland bolts evenly and symmetrically. If the gap between the gland and the valve stem is too small, the gap should be appropriately increased; if the gap between the gland and the valve stem is too large, it should be replaced.
no.2 Leakage of sealing surface
► Reason:
1. The top center of the connection between the valve stem and the closing part is suspended, incorrect or worn;
2. The quality of the sealing surface material is improperly selected or the valve is not selected according to the working conditions;
3. The valve stem is bent or improperly assembled, so that the closing part is skewed or misaligned;
4. The sealing surface is unevenly ground and cannot form a tight line;
► Maintenance method:
1. Correctly select the material and type of the gasket according to the working conditions;
2. The bolts should be tightened evenly and symmetrically, and a torque wrench should be used if necessary. The pre-tightening force should meet the requirements and should not be too large or small. There should be a certain pre-tightening clearance between the flange and the threaded connection;
3. The gasket assembly should be aligned at the center, the force is even, and the gasket is not allowed to overlap and use double gaskets;
4. If the static sealing surface is corroded, damaged and the processing quality is not high, it should be repaired, ground, and inspected for coloring to make the static sealing surface meet the relevant requirements;
5. Pay attention to cleaning when installing the gasket, the sealing surface should be cleaned with kerosene, and the gasket should not fall to the ground.
no.3 The closing part falls off and leaks
► Reason:
1. The operation is poor, so that the closing part is stuck or exceeds the top dead center, and the connection is damaged and broken;
2. The material of the connector is selected incorrectly, which cannot withstand the corrosion of the medium and the mechanical wear.
3. The connection of the closing part is not firm, and it is loose and falls off;
► Maintenance method:
1. Correct operation, close the valve can not be too forceful, open the valve can not exceed the top dead center, after the valve is fully opened, the handwheel should be reversed a little;
2. The connection between the closing part and the valve stem should be firm, and there should be a backstop at the threaded connection;
3. The fasteners used to connect the closing part and the valve stem should withstand the corrosion of the medium and have certain mechanical strength and wear resistance.
no.4 Leakage at the joint of the sealing ring
► Reason:
1. The sealing ring is not rolled tightly;
2. The connecting threads, screws and pressure rings of the sealing ring are loose;
3. The sealing ring is connected and corroded.
4. The sealing ring is welded with the body, and the surfacing quality is poor;
► Maintenance method:
1. Leakage at the sealing and rolling place should be injected with adhesive and then fixed by rolling;
2. The sealing ring should be re-welded according to the welding specification. When the surfacing weld cannot be repaired, the original surfacing welding and processing shall be removed;
3. Remove the screws, wash the pressure ring, replace the damaged parts, grind the sealing surface of the seal and the connection seat, and reassemble. For parts with large corrosion damage, it can be repaired by welding, bonding and other methods;
4. The connecting surface of the sealing ring is corroded and can be repaired by grinding, bonding and other methods. If it cannot be repaired, the sealing ring should be replaced.
no.5 Leakage of valve body and bonnet
► Reason:
1. The casting quality of iron castings is not high, and the valve body and valve cover body have defects such as blisters, loose structures, and slag inclusions;
2. Day freeze cracking;
3. The cast iron valve is damaged after being hit by heavy objects.
4. Poor welding, there are defects such as slag inclusion, non-welding, stress cracks, etc.;
► Maintenance method:
1. Improve casting quality, and conduct strength test in strict accordance with regulations before installation;
2. For valves with air temperature below 0° and 0°, they should be kept warm or heated, and the valves that are out of use should be drained of water;
3. The welding seam of the valve body and bonnet composed of welding shall be carried out according to the relevant welding operation regulations, and the flaw detection and strength test shall be carried out after welding;
4. It is forbidden to push and place heavy objects on the valve, and it is not allowed to hit cast iron and non-metallic valves with a hand hammer. The installation of large-diameter valves should have brackets.
► Specific treatment methods for valve body leakage:
Bonding
Taking advantage of the fast curing speed of the adhesive, the vicinity of the pin is filled with adhesive in time to establish a new solid sealing structure to achieve the purpose of preventing leakage. It is a method of plugging leakage under pressure by using the special function of the adhesive.
For the pressure medium and the blisters with small leakage, first grind the metal luster near the leakage point, and then use a taper pin to align the leakage point with appropriate force.
During operation, fix the top pressure mechanism on one side of the regulating valve, press the screw at high speed, so that the axial direction of the top pressure screw is facing the leakage point, rotate the top pressure screw, and use the rivet at the end of the top pressure screw to firmly press the leakage point. site, forcing the leak to stop.
welding method
A) When the pressure of the leaking medium in the valve body is low and the leakage is small, a nut with an inner diameter more than twice the leakage point can be used to allow the leaking medium to flow out from the nut, and the nut is welded on the valve body. Add a bolt of the same specification as the nut, place a rubber pad or asbestos pad at the bottom of the nut, wrap the top of the bolt with raw tape and screw it into the nut to prevent leakage.
For the valve body with high leakage medium pressure and large leakage, the drainage welding method can be used. First, use a piece of iron plate with a circular hole in the middle, weld an isolation valve with a diameter commensurate with the circular hole on the circular hole of the iron plate, open the isolation valve, and align the central hole of the iron plate with the leakage point and fit it to the valve body. Let the leaking medium flow out through the central hole of the iron plate and the isolation valve.
B) The leakage medium of the valve body is high temperature and high pressure, but the regulating valve has a large shape and size and the leakage amount is not large, and the welding method can also be used.
First, directly weld all the gaps related to the leakage point on the valve body (without welding the leakage point), and then use a length of pipe that meets the working conditions (working temperature, pressure) depending on the site environment (generally about 200mm) , its diameter should be larger than the leakage point, weld a regulating valve suitable for the pipe to one end of the pipe, and fully open the regulating valve, then align the other end of the pipe with the leakage point and weld it, then close the regulating valve to stop leakage.
If the bonding surface is not good, you can place a rubber or asbestos pad on the bonding surface, then weld the iron plate near the valve body, and then close the isolation valve to achieve the purpose of resealing.

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