1. Leakage of valve body and bonnet
1. The casting quality of iron castings is not high, and there are defects such as blisters, loose tissues, slag inclusions on the valve body and bonnet body;
2. Day freeze cracking;
3. Poor welding, there are defects such as slag inclusion, non-welding, stress cracks, etc.;
4. The cast iron valve is damaged after being hit by a heavy object.
► Maintenance method:
1. Improve the casting quality, and carry out the strength test in strict accordance with the regulations before installation;
2. Valves whose temperature is below 0° and 0° should be kept warm or mixed with heat, and the valves that are out of service should be drained of stagnant water;
3. The welding seam of the valve body and bonnet composed of welding should be carried out in accordance with the relevant welding operation regulations, and the flaw detection and strength test should be carried out after welding;
4. It is forbidden to push and put heavy objects on the valve, and it is not allowed to hit the cast iron and non-metal valves with a hand hammer. The installation of large-diameter valves should be provided with brackets.
► Specific treatment methods for valve body leakage:
1. Bonding method
Taking advantage of the fast curing speed of the adhesive, fill the vicinity of the pin with the adhesive in time to form a new solid sealing structure to achieve the purpose of preventing leakage. It is a method of using the special function of the adhesive to plug leaks under pressure.
For pressure medium and blisters with small leakage, you can first polish the vicinity of the leakage point to give a metallic luster, then use a tapered pin to aim at the leakage point and drive in with appropriate strength.
During operation, fix the top pressure mechanism on the side of the regulating valve, press the screw at high speed, make the axial direction of the top pressure screw face the leakage point, rotate the top pressure screw, and use the rivet at the end of the top pressure screw to firmly press against the leak. On the site, forcing the leak to cease.
2. Welding method
A) In the case that the leakage medium pressure of 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 let the leakage medium flow out of the nut, and the nut is welded to the valve body. Fit a bolt with the same specification as the nut, place a rubber pad or asbestos pad on the bottom of the nut, and screw the top of the bolt into the nut with raw tape to prevent leakage.
For the valve body with high leakage medium pressure and large leakage, drainage welding method can be used. First, use an iron plate with a round hole in the middle, weld an isolation valve with a diameter commensurate with the round hole on the round hole of the iron plate, open the isolation valve, and align the central hole of the iron plate with the leakage point and attach it to the valve body. Let the leakage medium flow out through the central hole of the iron plate and the isolation valve.
B) The leakage medium in the valve body is high temperature and high pressure, but the adjustment valve has a larger shape and size, and the leakage is not large. The welding method can also be used.
First, directly weld all the gaps related to the leakage point on the valve body (not welding the leakage point), and then use a length of pipe that meets the working conditions (working temperature, pressure) depending on the site environment (usually about 200mm) , Its diameter should be larger than the leakage point. Weld an adjusting valve that is compatible with the pipe to one end of the pipe, and fully open the adjustment valve, then take the other end of the pipe to the leakage point and weld it, then close the adjustment valve to stop it. 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 to the valve body, and then close the isolation valve to achieve the purpose of resealing.
2. Leakage at the filler
1. Wrong selection of packing, not resistant to medium corrosion, not resistant to valve high pressure or vacuum, high temperature or low temperature use;
2. The packing is installed incorrectly, there are defects such as replacing the big with the small, the spiral coiled joint is not good, and the tightening and loosening are present;
3. The filler has exceeded the service life, has aged and lost its elasticity;
4. The valve stem is not high in precision and has defects such as bending, corrosion, and wear;
5. The number of packing circles is insufficient and the gland is not pressed tightly;
6. The gland, bolts, and other parts are damaged, making the gland unable to be compressed;
7. Improper operation, excessive force, etc.;
8. The gland is skewed, and the gap between the gland and the valve stem is too small or too large, causing the valve stem to wear and the packing to damage.
► Maintenance method:
1. The material and type of filler should be selected according to the working conditions;
2. Install the packing correctly according to the relevant regulations, the packing should be placed and compressed one by one, and the joint should be 30℃ or 45℃;
3. The packing that has been used for a long time, is aging, or is damaged should be replaced in time;
4. After the valve stem is bent or worn, it should be straightened and repaired. If it is seriously damaged, 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 compression sleeve should have a pre-tightening gap of more than 5mm;
6. Damaged glands, bolts and other parts 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. The gland bolts should be tightened evenly and symmetrically. If the gap between the gland and the valve stem is too small, the gap should be appropriately increased; the gap between the gland and the valve stem should be too large and should be replaced.
Third, the leakage of the sealing surface
1. The sealing surface is unevenly ground and cannot form a tight line;
2. The top center of the connection between the valve stem and the closing part is suspended, incorrect or worn;
3. The valve stem is bent or incorrectly assembled, which makes the closing member skewed or misaligned;
4. Improper selection of the quality of the sealing surface material or failure to select the valve according to the working conditions.
► 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. If necessary, a torque wrench should be used. The pre-tightening force should meet the requirements and should not be too large or small. There should be a certain pre-tightening gap between the flange and the threaded connection;
3. The gasket assembly should be aligned at the center, and the force should be even. The gasket is not allowed to overlap or use double gaskets;
4. The static sealing surface is corroded, damaged, and the processing quality is not high. Repair, grinding, and color inspection should be carried out 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.
4. Leakage at the joint of the sealing ring
1. The sealing ring is not tightly rolled;
2. The sealing ring is welded to the body, and the surfacing quality is poor;
3. The sealing ring connection thread, screw and pressing ring are loose;
4. The sealing ring is connected and corroded.
► Maintenance method:
1. Leakage at the seal rolling area should be filled with adhesive and then rolled to fix it;
2. The sealing ring should be repaired according to the welding specification. The original surfacing and processing should be removed when the surfacing welding cannot be repaired;
3. Remove the screws and pressure ring to clean, replace the damaged parts, grind the sealing surface and the connecting seat, and reassemble. For parts with large corrosion damage, welding, bonding and other methods can be used to repair;
4. The connecting surface of the sealing ring is corroded, it can be repaired by grinding, bonding and other methods. If it cannot be repaired, the sealing ring should be replaced.
Fifth, the closure part falls off and causes leakage
1. Poor operation makes the closing piece stuck or exceeds the top dead center, and the connection is damaged and broken;
2. The closing part is not firmly connected, loose and fall off;
3. The wrong connection material is selected, which cannot withstand the corrosion of the medium and mechanical abrasion.
► Maintenance method:
1. Operate correctly, do not use too much force to close the valve, and open the valve not to exceed the top dead center. After the valve is fully opened, the handwheel should be reversed a little;
2. The closing piece and the valve stem should be firmly connected, and the threaded connection should have a backstop;
3. The fastener used to connect the closing part and the valve stem should withstand the corrosion of the medium, and have a certain degree of mechanical strength and wear resistance.