Causes and solutions for valve leakage

The requirements for valve sealing performance should be based on the prevention of leakage. Depending on the different parts and degrees of leakage, the leakage of the valve is different. Therefore, different anti-leakage measures need to be proposed.

1. Leakage caused by the closure falling off

Reasons:
(1) Improper operation, causing the closure to get stuck or exceed the top dead center, and the connection to be damaged and broken;
(2) The closure is not firmly connected, loose and falls off;
(3) The material of the connection is not correct and cannot withstand the corrosion of the medium and mechanical wear.

Maintenance method:
(1) Correct operation, do not use too much force to close the valve, do not open the valve beyond the top dead center, and the handwheel should be reversed slightly after the valve is fully opened;
(2) The connection between the closure and the valve stem should be firm, and there should be a stopper at the threaded connection;
(3) The fasteners used to connect the closure and the valve stem should withstand the corrosion of the medium and have a certain mechanical strength and wear resistance.

2. Leakage at the packing (the leakage of the valve, the proportion of the packing is the largest)

Reasons:
(1) The packing is not selected correctly, it is not resistant to the corrosion of the medium, and it 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, there are defects such as small instead of large, poor spiral winding joints, tight top and loose bottom;
(3) The packing has exceeded its service life, has aged, and has lost its elasticity;
(4) The valve stem is not accurate, with defects such as bending, corrosion, and wear;
(5) The number of packing turns is insufficient, and the gland is not tightened;
(6) The gland, bolts, and other parts are damaged, making it impossible to tighten the gland;
(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 methods:
(1) The material and type of packing should be selected according to the working conditions;
(2) The packing should be installed correctly according to relevant regulations. The packing should be placed and tightened one circle at a time, and the joint should be 30℃ or 45℃;
(3) The packing that has been used for a long time, aged, or damaged should be replaced in time;
(4) The rod should be straightened and repaired after bending or wear, and the seriously damaged one should be replaced in time;
(5) The packing should be installed according to the specified number of circles, the gland should be tightened symmetrically and evenly, and the gland should have a pre-tightening clearance of more than 5mm;
(6) Damaged glands, bolts and other parts should be repaired or replaced in time;
(7) The operating procedures should be followed. Except for the impact handwheel, it should be operated at a uniform speed and normal force;
(8) The gland bolts should be tightened evenly and symmetrically. If the gap between the gland and the valve stem is too small, it should be appropriately increased; if the gap between the gland and the valve stem is too large, it should be replaced.

3. Leakage of the sealing surface

Reasons:
(1) The sealing surface is not ground flat and cannot form a sealing line;
(2) The top center of the connection between the valve stem and the closing part is suspended, misaligned or worn;
(3) The valve stem is bent or assembled incorrectly, causing the closing part to be skewed or misaligned;
(4) The quality of the 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) Carefully adjust and operate smoothly;
(3) The bolts should be tightened 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 too small. There should be a certain pre-tightening gap between the flange and the threaded connection;
(4) The gasket assembly should be aligned with the center and the force should be evenly applied. The gasket is not allowed to overlap or use double gaskets;
(5) The static sealing surface is corroded, damaged, or the processing quality is not high. It should be repaired, ground, and color checked to make the static sealing surface meet the relevant requirements;
(6) When installing the gasket, attention should be paid to cleaning. The sealing surface should be cleaned with kerosene and the gasket should not fall to the ground.

4. Leakage at the sealing ring connection

Reason:
(1) The sealing ring is not rolled tightly;
(2) The sealing ring is welded to the body and the surfacing quality is poor;
(3) The sealing ring connection thread, screw, and pressure ring are loose;
(4) The sealing ring is connected and corroded.

Maintenance method:
(1) If the sealing rolling leaks, the adhesive should be injected and then rolled and fixed;
(2) The sealing ring should be re-welded according to the welding specifications. When the weld cannot be repaired, the original weld should be removed and processed;
(3) Remove the screws and pressure rings, clean them, replace the damaged parts, grind the sealing and connecting seat sealing surfaces, and reassemble. For parts with large corrosion damage, welding, bonding and other methods can be used to repair;
(4) If the sealing ring connection surface is corroded, it can be repaired by grinding, bonding and other methods. If it cannot be repaired, the sealing ring should be replaced.

5. Leakage of valve body and valve cover:

 Reason:
(1) The casting quality of cast iron parts is not high, and there are defects such as sand holes, loose structure, slag inclusions, etc. on the valve body and valve cover;
(2) Cold cracking;
(3) Poor welding, with defects such as slag inclusions, unwelded, stress cracks, etc.;
(4) Cast iron valves are damaged after being hit by heavy objects.

Maintenance methods:
(1) Improve casting quality and conduct strength tests in strict accordance with regulations before installation;
(2) Valves in temperatures of 0° and below should be insulated or heated, and valves that are out of use should be drained of accumulated water;
(3) The welds of the valve body and valve cover composed of welding should be carried out in accordance with relevant welding operating procedures, and flaw detection and strength tests should be carried out after welding;
(4) It is forbidden to push or place heavy objects on the valve, and it is not allowed to hit cast iron and non-metallic valves with a hammer. Large-diameter valves should be installed with brackets.