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. For valves with air temperature of 0 ℃ and below, heat preservation or mixing shall be carried out, and ponding shall be removed for valves out of service;
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 not allowed to push or put heavy objects on the valve. It is not allowed to hit cast iron and non-metallic valves with a hammer. Large diameter valves should be installed with supports.
Leakage at packing
The proportion of the valve leakage at the packing is larger.
reason:
1. The packing is not selected correctly, and is not resistant to medium corrosion, high pressure or vacuum, high temperature or low temperature of the valve;
2. The packing is installed incorrectly, and there are defects such as replacing the big with the small, poor spiral winding joints, tightening and loosening;
3. The filler has expired, aged and lost elasticity;
4. The precision of the valve rod is not high, and there are defects such as bending, corrosion and wear;
5. The number of packing rings is insufficient, and the gland is not compacted;
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 askew, and the clearance between the gland and the valve rod is too small or too large, which causes the valve rod to be worn and the packing to be damaged.
Maintenance method:
1. The material and type of filler shall be selected according to working conditions;
2. The packing shall be installed correctly according to the relevant regulations, the packing shall be placed and compacted circle by circle, and the joint shall be at 30 ℃ or 45 ℃;
3. The filler with long service life, aging and damage shall be replaced in time;
4. Straighten and repair the bent and worn valve rod, and replace the seriously damaged valve rod 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 gland shall have a preload 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 followed, except for the impact handwheel, which shall be operated with normal force at a constant speed;
8. The gland bolts shall be tightened evenly and symmetrically. If the clearance between the gland and the valve stem is too small, the clearance shall be increased appropriately; The clearance between the gland and the valve rod is too large, which should be replaced.
Leakage of sealing surface
reason:
1. The sealing surface is not smooth and cannot form a sealing line;
2. The top center of the connection between the valve rod and the closing piece is suspended, misaligned or worn;
3. The valve rod is bent or improperly assembled, which makes the closing piece skewed or out of alignment;
4. The quality of sealing surface material is improper or the valve is not selected according to the working conditions.
Maintenance method:
1. Correctly select the material and type of the 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. The flange and threaded connection shall have a certain pre tightening clearance;
4. The gasket assembly shall be aligned in the middle, and the force shall be uniform. The gasket shall not be overlapped or double gaskets shall be used;
5. If the static sealing surface is corroded, damaged, processed, and the processing quality is not high, repair, grind, and dye check shall be carried out to make the static sealing surface meet the relevant requirements;
6. When installing the gasket, pay attention to cleaning, the sealing surface shall be cleaned with kerosene, and the gasket shall not fall to the ground.
Leakage at the joint of sealing ring
reason:
1. The seal ring is not tightly rolled;
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 connected and corroded.
Maintenance method:
1. The leakage at the seal rolling part shall be fixed by injecting adhesive and then rolling;
2. The sealing ring shall be repaired according to the welding specification. The original surfacing and processing shall be removed when the surfacing cannot be repaired;
3. Remove the screws and pressure rings for cleaning, replace the damaged parts, grind the sealing surface of the seal and connection seat, and reassemble. The parts with large corrosion damage can be repaired by welding, bonding and other methods;
4. If the joint surface of the seal ring is corroded, it can be repaired by grinding, bonding and other methods. If it cannot be repaired, replace the seal ring.
Leakage due to falling off of the closing element
reason:
1. Poor operation causes the closing piece to be stuck or exceed the top dead point, and the connection is damaged and broken;
2. The closing piece is not firmly connected and falls off due to looseness;
3. The materials of the selected connecting pieces are not correct and can not withstand the corrosion of medium and mechanical wear.
Maintenance method:
1. Correct operation. Do not use too much force to close the valve, and 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 closure and valve rod shall be firmly connected, and the threaded connection shall be provided with a stopper;
3. Fasteners used to connect the closure and valve stem shall withstand the corrosion of medium and have certain mechanical strength and wear resistance.
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