Home > News > Content

Valve Leakage Causes And Solutions

Aug 01, 2019

Valve body and bonnet leakage

the reason:  

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

2, freezing and 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 heavy objects.

Maintenance method:

1. Improve the casting quality and conduct the strength test strictly according to the regulations before installation;

2. For valves with temperatures below 0 °C and below 0 °C, heat or heat should be applied. Valves that are stopped should be drained;

3. The welds of the valve body and bonnet composed of welding shall be carried out in accordance with the relevant welding operation procedures, and the 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 the cast iron and non-metal valves with the hammer. The installation of the large diameter valve should have the bracket.

Leakage at the packing

The outer leakage of the valve, the proportion of the filler is the largest.

the reason:  

1. The filler is not used correctly, it is not resistant to the corrosion of the medium, and is not resistant to the high pressure of the valve or the use of vacuum, high temperature or low temperature;

2, the filler is not installed correctly, there are defects such as small generation, poor spiral coiled joints, tight and loose;

3, the filler exceeds the use period, has aged, lost flexibility;

4, the valve stem accuracy is not high, there are defects such as bending, corrosion, wear;

5. The number of packing rings is insufficient, and the gland is not pressed;

6. The gland, bolts, and other components are damaged, so that the gland cannot be pressed;

7, improper operation, excessive force, etc.;

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

Maintenance method:

1. The materials and types of fillers should be selected according to working conditions;

2. According to the relevant regulations, the packing should be installed correctly. The packing should be placed in a ring-by-turn manner, and the joint should be 30 ° C or 45 ° C;

3. Filling materials that are too long, aging and damaged should be replaced in time;

4. After the valve stem is bent and worn, it should be straightened and repaired. If the damage is serious, it should be replaced in time;

5, the packing should be installed according to the specified number of turns, the gland should be tightly and symmetrically tightened, and the press sleeve should have a pre-tightening clearance of more than 5mm;

6. Damaged glands, bolts and other components shall be repaired or replaced in time;

7, should abide by the operating procedures, in addition to the impact type hand wheel, operate at a constant speed normal force;

8. The gland bolt should be tightened evenly and symmetrically. The gap between the gland and the valve stem should be too small. The gap should be increased properly. The gap between the gland and the valve stem should be too large and should be replaced.

Leakage of the sealing surface

the reason:  

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

2. The top of the joint between the valve stem and the closing member is suspended, not worn or worn;

3, the valve stem is bent or improperly assembled, so that the closing member is skewed or not in the middle;

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

Maintenance method:

1. Correctly select the materials and types of the underlying gasket according to the working conditions;

2, carefully adjusted, smooth operation;

3. The bolt should be screwed evenly and symmetrically. If necessary, a torque wrench should be used. The pre-tightening force should meet the requirements and should not be too large or small. There should be a certain pre-tightening clearance between the flange and the threaded joint;

4, the gasket assembly should be aligned in the middle, the force is even, the gasket is not allowed to overlap and use double gasket;

5, static sealing surface corrosion, damage processing, processing quality is not high, should be repaired, polished, coloring inspection, so that the static sealing surface meets relevant requirements;

6. When installing the gasket, pay attention to cleaning. Apply kerosene to the sealing surface. The gasket should not fall to the ground.

Leakage at the seal of the seal

the reason:  

1. The sealing ring is not pressed tightly;

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

3. The sealing ring is connected with thread, screw and pressure ring;

4. The sealing ring is connected and corroded.

Maintenance method:

1. Leakage at the sealing pressure should be filled with adhesive and then fixed;

2. The sealing ring should be repaired by the welding specification. The original surfacing and processing shall be removed when the surfacing is unable to repair the welding;

3. Remove the screws and pressure ring to clean, replace the damaged parts, grind the sealing and sealing joints, and reassemble. For parts with large corrosion damage, they can be repaired by welding or bonding;

4. The sealing surface of the sealing ring is corroded and can be repaired by grinding or bonding. If it cannot be repaired, the sealing ring should be replaced.

Closed parts fall off and leak

the reason:  

1. Poor operation, causing the closing piece to be stuck or exceeding the top dead center, and the joint is damaged and broken;

2, the closing parts are not firmly connected, loose and fall off;

3, the selection of the connector material is wrong, can not withstand the corrosion of the media and mechanical wear.

Maintenance method:

1. Correct operation, the valve can not be used too much force, the opening valve can not exceed the top dead center, after the valve is fully open, the hand wheel should be reversed a little;

2. The connection between the closing piece and the valve stem should be firm, and the threaded joint should have a stop piece;

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