01 leakage of valve body and bonnet
reason:
1. the casting quality of iron castings is not high, and there are sand holes, loose structures, slag inclusions and other defects on the valve body and bonnet body
2. cold weather and frost crack;
3. poor welding, slag inclusion, non welding, stress crack and other defects;
4. the cast iron valve is damaged after being hit by heavy objects.
Maintenance method:
1. improve casting quality and conduct strength test in strict accordance with regulations before installation;
2. valves with air temperature between 0 ° and below 0 ° shall be insulated or heated, and valves out of service shall be drained of accumulated water
3. the welds of valve body and bonnet composed of welding shall be carried out according to relevant welding operation procedures, and flaw detection and strength test shall be carried out after welding;
4. it is forbidden to push or put heavy objects on the valve. It is not allowed to hit cast iron and non-metallic valves with a hammer. The installation of large-diameter valves should have a support.
02 leakage at packing
reason:
1. the packing is not selected correctly, which is not resistant to medium corrosion, and is not resistant to the use of high pressure or vacuum, high temperature or low temperature of the valve;
2. the packing is not installed correctly, and there are defects such as substituting small for large, poor spiral wound joint, tightening and loosening;
3. the filler has expired, aged and lost elasticity
4. the valve rod has low precision, bending, corrosion, wear and other defects
5. the number of packing rings is insufficient and the gland is not compacted;
6. the gland, bolts and other parts are damaged, so that the gland cannot be pressed tightly;
7. improper operation, excessive force, etc;
8. the gland is skewed, and the gap between the gland and the valve rod is too small or too large, resulting in wear of the valve rod and damage of the packing.
Maintenance method:
1. materials and types of fillers shall be selected according to working conditions;
2. the packing shall be installed correctly according to relevant regulations, the packing shall be placed and compacted one by one, and the joint shall be 30 ℃ or 45 ℃;
3. the fillers with long service life, aging and damage shall be replaced in time;
4. the valve rod shall be straightened and repaired after bending and wear, and the seriously damaged valve rod shall be replaced in time;
5. the packing shall be installed according to the specified number of turns, the gland shall be tightened symmetrically and evenly, and the compression sleeve shall have a pre tightening clearance of more than 5mm;
6. damaged glands, bolts and other parts shall be repaired or replaced in time;
7. the operating procedures shall be observed. Except for the impact type handwheel, the operation shall be carried out with constant speed and normal force;
8. the gland bolts shall be tightened evenly and symmetrically. If the clearance between the gland and the valve rod is too small, the clearance shall be appropriately increased; The clearance between the gland and the valve rod is too large and should be replaced.
03 leakage of sealing surface
reason:
1. The sealing surface is unevenly ground and cannot form a sealing line;
2. The top center of the connection between the valve rod and the closing part is suspended, incorrect or worn;
3. The valve rod is bent or improperly assembled, so that the closing part is skewed or out of alignment;
4. Improper selection of sealing surface materials or failure to select valves according to working conditions
Maintenance method:
1. Correctly select the material and type of bump gasket according to the working conditions;
2. Careful adjustment and stable operation;
3. The bolts shall be tightened evenly and symmetrically. If necessary, a torque wrench shall be used. The pre tightening force shall meet the requirements and shall not be too large or small. There shall be sufficient pre tightening clearance at the flange and threaded connection;
4. The gasket assembly shall be aligned and stressed evenly, and the gasket is not allowed to overlap or use double gaskets;
5. If the static sealing surface is corroded, damaged and processed, and the processing quality is not high, repair, grind and dye inspection shall be carried out to make the static sealing surface meet the relevant requirements;
6. Pay attention to cleaning when installing the gasket. The sealing surface should be cleaned with kerosene. The gasket should not fall to the ground.
04 leakage at seal ring connection
reason:
1. The sealing ring is not rolled tightly
2. The sealing ring is welded with the body, and the surfacing quality is poor;
3. The connecting thread, screw and pressure ring of the sealing ring are loose;
4. The sealing ring is corroded due to connection.
Maintenance method:
1. If there is leakage at the sealing rolling position, the adhesive shall be injected and then rolled and fixed;
2. The sealing ring shall be re welded according to the welding specification. The original surfacing and processing shall be removed if the surfacing cannot be repaired;
3. Remove the screws and pressure rings, clean them, replace the damaged parts, grind the sealing surface between the seal and the connecting seat, and reassemble them. The parts with large corrosion damage can be repaired by welding, bonding and other methods;
4. If the connecting surface of the sealing ring is corroded, it can be repaired by grinding, bonding and other methods. If it cannot be repaired, replace the sealing ring.
05 leakage due to falling off of closing parts
reason:
1. The closing part is stuck or exceeds the top dead center due to poor operation, and the connection is damaged and broken;
2. The closing parts are not firmly connected, loose and fall off;
3. The material of the selected connector is incorrect and cannot withstand the corrosion of the medium and mechanical wear.
Maintenance method:
1. Operate correctly. Do not use excessive force to close the valve. Do not open the valve beyond the top dead center. After the valve is fully opened, the handwheel should be reversed a little;
2. The closing part shall be firmly connected with the valve rod, and the threaded connection shall be provided with a retaining part;
3. The fasteners used for connecting the closing part and the valve rod shall withstand the corrosion of the medium and have sufficient mechanical strength and wear resistance.