Cause analysis and solution of valve leakage

Author:     Published time:2022-05-21 10:00     Reading times:83    


A Leakage due to falling off of closing parts


reason:

1. Poor operation, so that the closing part is stuck or exceeds the top dead center, 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, 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 connection between the closing part and the valve rod shall be firm, and the threaded connection shall have a non-return part;

3. The fasteners used for connecting the closing part and the valve rod shall withstand the corrosion of the medium and have certain mechanical strength and wear resistance.


B  Leakage at the packing (for the external leakage of the valve, the proportion of packing is the largest)

reason:

1. The packing is not selected correctly, which is not resistant to medium corrosion, 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 replacing large with small, poor spiral wound joint, 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 compressed;

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 the wear of the valve rod and the damage of the packing.

Maintenance method:

1. The material and type of filler shall be selected according to the working conditions;
2. The packing shall be installed correctly according to relevant regulations, the packing shall be placed and pressed one by one, and the joint shall be 30 ℃ or 45 ℃; 3. The filler 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 gland, bolts and other parts shall be repaired or replaced in time;

7. The operating procedures shall be observed. Except for the impact 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 gland and valve rod is too large and should be replaced.


C、 Leakage 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 stem 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 material quality or failure to select valve 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 shall be used. The preload shall meet the requirements and shall not be too large or small. There shall be a certain 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 the processing quality is not high, it shall be repaired, grinded and checked for coloring to make the static sealing surface meet the relevant requirements;


6. Pay attention to cleaning when installing the gasket. The sealing surface shall be cleaned with kerosene, and the gasket shall not fall to the ground.


D  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 the connection.

Maintenance method:

1. The leakage at the sealing rolling position shall be filled with adhesive and then rolled and fixed;

2. The sealing ring shall be re welded according to the welding specification. If repair welding cannot be carried out at the surfacing position, the original surfacing and processing shall be removed;

3. Remove the screw and pressure ring, clean, replace the damaged parts, grind the sealing surface between the seal and the connecting seat, and reassemble. 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.


E Leakage of valve body and bonnet:

reason:

1. The casting quality of iron castings is not high, and there are sand holes, loose structure, slag inclusion 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 ponding 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 and put heavy objects on the valve. It is not allowed to hit cast iron and non-metallic valves with a hammer. Large diameter valves shall be installed with supports.

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