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Cause analysis and solution of valve leakage

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Update time : 2020-06-11 15:06:50
Zhejiang Oss Valve co Ltd is an excellent valve manufacturer in China Wenzhou City.The products include ball valve,gate valve,globe valve,check valve,DBB valve,sight glass,Y strainer,filter,T strainer,basket strainer,pinch valve.
First,The reason of the leakage caused by closing part
1). Poor operation makes the closing piece stuck or exceeds the top center, and the connection is damaged and broken;
2). The connection of the closing piece is not firm, and it falls off loosely;
3). The material of the connecting piece is wrong, and it can not bear the corrosion of the medium.
 
Maintenance method:
1). For correct operation, the valve cannot be closed with excessive force, and the valve cannot be opened above 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.

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Second, the leakage at the packing (the leakage of the valve, the proportion of the packing is the largest)
the reason:
1. Wrong choice of filler, not resistant to medium corrosion, high pressure or vacuum, high temperature or low temperature of the valve; 2. Improper installation of the filler, there are defects such as small and large, poor spiral coiled joints, tight tightening and loosening;
3. The filler has exceeded its service life, has aged and lost its elasticity
4. The precision of the valve stem is not high, there are defects such as bending, corrosion, wear, etc.
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 out 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 according to the relevant regulations, the packing should be placed and tightened circle by circle, and the joint should be 30°C or 45°C; 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 pre-tightening gap of more than 5mm;
6. Damaged gland, bolt and other parts should be repaired or replaced in time;
7. Observe the operating regulations, except for the impact handwheel, operate with normal speed and normal force;
8. The gland bolts should be tightened evenly and symmetrically. The gap between the gland and the stem is too small, and the gap should be increased appropriately; the gap between the gland and the stem is too large and should be replaced.
Third, Leakage of the sealing surface
the 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 the assembly is not correct, so that the closing piece is 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.
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Maintenance method:
1. Select the material and type of the gasket according to the working conditions;
2. Careful adjustment and smooth operation;
3. The bolts should be tightened evenly and symmetrically. If necessary, a torque wrench should be used. The pretension should meet the requirements, not too large or small. There should be a certain pre-tightening gap between the flange and the thread connection;
4. The gasket assembly should be centered and aligned, and the force is uniform. The gasket is not allowed to overlap and use double gaskets;
5. 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;
6. Please 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.
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Fourth ,Leakage at the joint of the sealing ring
the 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. A
 
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 repaired in accordance with the welding specifications. When 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 sealing ring is corroded, and it can be repaired by grinding, bonding, etc., and the sealing ring should be replaced when it cannot be repaired.
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Fifth, Leakage of valve body and valve cover:
the reason:
1. The casting quality of the cast iron parts is not high, and the valve body and the valve cover body have defects such as sand holes, loose structure, and slag inclusion.
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. A
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 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 welds of the valve body and valve cover composed of welding should be in accordance with the relevant welding operation regulations. Carry out, after welding, flaw detection and strength test should also be carried out;
4. It is forbidden to push and place heavy objects on the valve, and it is not allowed to hit the cast iron and non-metallic valves with a hammer. The installation of large-diameter valves should have a bracket.