Five situations of valve leakage and countermeasures

Update:17 Apr 2020

1. Leakage of valve body and bonnet

► Reason:

1. The casting quality of the cast iron parts is not high, and there are defects such as sand holes, loose structure and slag inclusion on the valve body and valve cover body;

2. Freeze cracking;

3. Poor welding, there are defects such as slag inclusion, unwelded, stress cracks;

4. The cast iron valve is damaged after being hit by a heavy object.

► Maintenance method:

1. Improve the casting quality, and perform the strength test in strict accordance with the regulations before installation;

2. For valves with air temperature below 0 ° and below 0 °, heat preservation or heat mixing should be carried out, and the valves that are out of service should be excluded from accumulated water;

3. The welding seam of the valve body and valve cover composed of welding shall be carried out in accordance with the relevant welding operation regulations, and the flaw detection and strength test shall be carried out after welding;

4. It is forbidden to push or release heavy objects on the valve, and it is not allowed to hit the cast iron and non-metallic valves with a hand hammer. The installation of large-diameter valves should have a bracket.

► Specific treatment methods for valve body leakage:

1. Bonding method

Taking advantage of the fast curing speed of the adhesive, the adhesive should be coated with adhesive in a timely manner to establish a new solid sealing structure to achieve the purpose of stopping leakage. It is a method of plugging leaks with pressure using the special function of adhesive.

For the pressure medium and the trachoma with small leakage volume, you can first polish the metal gloss near the leakage point, and then use the taper pin to align the leakage point and drive in with appropriate strength.

During operation, the top pressure mechanism is fixed on the side of the regulating valve. The high-speed top pressure screw makes the axis of the top pressure screw face the leakage point. Rotate the top pressure screw and use the rivets at the end of the top pressure screw to firmly press the leak At the site, the leak is forced to stop.

2. Welding method

A) When the leakage medium pressure of the valve body is low and the leakage volume 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 weld the nut to the valve body. Then add a bolt with the same specifications as the nut, put a rubber pad or asbestos pad on the bottom of the nut, screw the top of the bolt around the raw tape and screw it into the nut to achieve the purpose of preventing leakage.

For the valve body with high leakage medium pressure and large leakage volume, drainage welding method can be used. First, use an iron plate with a round hole in the middle. Weld an isolation valve commensurate with the round hole to the round hole of the iron plate. Open the isolation valve and fit the center hole of the iron plate to the leakage point and fit it to the valve body. Let the leaked medium flow out through the center hole of the iron plate and the isolation valve.

B) The leakage medium in the valve body is of high temperature and high pressure, but the adjustment valve has a large shape and size, and the leakage amount is not large. Welding can also be used.

First, directly weld all the gaps on the valve body related to the leakage point (not weld the leakage point), and then use a length of pipe that meets the working conditions (working temperature, pressure) according to the site environment (generally about 200mm) , Its diameter should be greater than the leak point, weld a regulating valve suitable for the pipe to one end of the pipe, and fully open the regulating valve, then weld the other end of the pipe to the leak point, and close the regulating valve to stop leakage.

If the bonding surface is not good, you can place rubber or asbestos pads 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 packing

► Reason:

1. Wrong choice of filler, not resistant to medium corrosion, not tolerant to high pressure or vacuum, high temperature or low temperature of the valve;

2. The packing is not installed correctly, there are defects such as small-to-large, bad spiral coiled joints, loose tightening, etc .;

3. The filler exceeds the service period, has aged and lost its elasticity;

4. The precision of the valve stem is not high, and there are 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, so that the gland cannot be compressed;

7. Improper operation, excessive force, etc .;

8. The gland is skewed, and the gap between the gland and the stem is too small or too large, causing the stem to wear and the packing to be damaged.

► Maintenance method:

1. The material and type of filler should be selected according to the working conditions;

2. Install the packing correctly in accordance with relevant regulations, the packing should be placed tightly circle by circle, and the joint should be 30 ℃ or 45 ℃;

3. Packing that is too long, aging or 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 pressure sleeve should have a preload gap of more than 5mm;

6. Damaged gland, bolt and other parts should be repaired or replaced in time;

7. The operating rules should be followed, except for the impact handwheel, with normal speed and normal force operation;

8. The gland bolts should be tightened evenly and symmetrically. If the gap between the gland and the stem is too small, the gap should be increased appropriately.

3. Leakage of the sealing surface

► Reason:

1. The sealing surface is unevenly ground and cannot form a close line;

2. The top of the connection between the valve stem and the closing piece is suspended, incorrect or worn;

3. The valve stem is bent or incorrectly assembled, causing the closing piece to be skewed or out of alignment;

4. The quality of the sealing surface material is not selected properly or the valve is not selected according to the working conditions.

► Maintenance method:

1. 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 preload should meet the requirements, not too large or small. There should be a certain pre-tightening gap between the flange and the thread connection;

3. The gasket assembly should be aligned and aligned evenly, and the stress is uniform. The gasket is not allowed to overlap and 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 clean 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

► Reason:

1. The sealing ring is not rolled tightly;

2. The sealing ring is welded to the body, and the quality of the surfacing is poor;

3. The connection thread, screw and pressure ring of the seal ring are loose;

4. The sealing ring is connected and corroded.

► Maintenance method:

1. Leakage at the sealing and rolling place should be injected with adhesive and then fixed by rolling;

2. Sealing ring should be repaired according to the welding specification. If the welding cannot be repaired, the original welding and processing should be removed;

3. Remove the screws and wash the pressure ring, replace the damaged parts, grind the sealing surface of the seal and the connecting seat, and reassemble. Welding, bonding and other methods can be used to repair parts with large corrosion damage;

4. The connection surface of the seal ring is corroded, and it can be repaired by grinding, bonding, etc., and the seal ring should be replaced when it cannot be repaired.

5. Leakage caused by closing parts

► Reason:

1. Poor operation makes the closing piece stuck or exceeds the top dead center, and the connection is damaged and broken;

2. The closing piece is not firmly connected, loose and fall off;

3. The material of the selected connector is wrong, and it cannot withstand the corrosion of the medium and mechanical wear.

► Maintenance method:

1. For correct operation, close the valve without excessive force, 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 connection between the closing part and the valve stem should be firm, and there should be a retreat part at the threaded connection;

3. The fastener used to connect the closing piece to the valve stem should withstand the corrosion of the medium and have a certain mechanical strength and wear resistance.