In the daily use of butterfly valves, various failures are often encountered. The leakage of the valve body and bonnet of the butterfly valve is one of the many failures. What is the reason for this phenomenon? Are there any other glitches to be aware of? The TWS Valve summarizes the following situation,
Part 1, Leakage of valve body and bonnet
1. The casting quality of iron castings is not high, and there are defects such as blisters, loose structures, and slag inclusions on the valve body and valve cover body;
2. The sky is freezing and cracking;
3. Poor welding, there are defects such as slag inclusion, unwelded, stress cracks, etc.;
4. The cast iron butterfly valve is damaged after being hit by heavy objects.
maintenance method
1. To improve casting quality, carry out strength test in strict accordance with regulations before installation;
2. For butterfly valves with temperatures below 0°C and below, they should be kept warm or heated, and the butterfly valves that are out of use should be drained of accumulated water;
3. The welding seam of the valve body and bonnet composed of welding should be carried out in accordance with the relevant welding operation procedures, and flaw detection and strength tests should be carried out after welding;
4. It is forbidden to push and place heavy objects on the butterfly valve, and it is not allowed to hit cast iron and non-metallic butterfly valves with hand hammers. The installation of large-diameter butterfly valves should have brackets.
Part 2. Leakage at packing
1. Wrong choice of filler, not resistant to medium corrosion, not resistant to high pressure or vacuum, high temperature or low temperature use of butterfly valve;
2. The packing is installed incorrectly, and there are defects such as substituting small for large, poor spiral coil joints, tight top and loose bottom;
3. The filler has aged and lost its elasticity beyond the service life;
4. The precision of the valve stem is not high, and there are defects such as bending, corrosion, and wear;
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 pressed tightly;
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, resulting in wear of the valve stem and damage to the packing.
maintenance method
1. The material and type of filler should be selected according to the working conditions;
2. Correctly install the packing according to the relevant regulations, the packing should be placed and compacted one by one, and the joint should be at 30°C or 45°C;
3. Packing with long service life, aging and damage should be replaced in time;
4. After the valve stem is bent and worn, it should be straightened and repaired, and the damaged one 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 gland should have a pre-tightening gap of more than 5mm;
6. Damaged glands, bolts and other components should be repaired or replaced in time;
7. The operating procedures should be followed, except for the impact handwheel, operate at a constant 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, the gap should be increased appropriately; if the gap between the gland and the valve stem is too large, it should be replaced.
Part 3 Leakage of the sealing surface
1. The sealing surface is not ground flat and cannot form a close line;
2. The top center of the connection between the valve stem and the closing member is suspended, incorrect or worn;
3. The valve stem is bent or assembled incorrectly, causing the closing parts to be skewed or out of center;
4. The quality of the sealing surface material is not selected properly 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 smooth operation;
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 small. There should be a certain pre-tightening gap between the flange and the threaded connection;
4. The assembly of the gasket should be aligned in the middle, and the force should be 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. Repairs, grinding, and coloring inspections should be carried out to make the static sealing surface meet the relevant requirements;
6. When installing the gasket, pay attention to cleanliness. The sealing surface should be cleaned with kerosene, and the gasket should not fall to the ground.
Part 4. Leakage at the joint of the sealing ring
1. The sealing ring is not rolled tightly;
2. The sealing ring is welded to the body, and the quality of surfacing 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. For leaks at the sealing rolling place, adhesive should be injected and then rolled and fixed;
2. The sealing ring should be rewelded according to the welding specification. When the surfacing welding cannot be repaired, the original surfacing welding and processing should be removed;
3. Remove the screws, clean the pressure ring, replace the damaged parts, grind the sealing surface and the connecting seat, and reassemble. For parts with large corrosion damage, it can be repaired by welding, bonding and other methods;
4. The connecting surface of the sealing ring is corroded, which can be repaired by grinding, bonding, etc. If it cannot be repaired, the sealing ring should be replaced.
Part 5. Leakage occurs when the closure falls off
1. Poor operation causes the closing parts to be stuck and the joints to be damaged and broken;
2. The connection of the closing part is not firm, loose and falls off;
3. The material of the connecting piece is not selected, and it cannot withstand the corrosion of the medium and the wear of the machine.
maintenance method
1. Correct operation, close the butterfly valve without excessive force, and open the butterfly valve without exceeding the top dead point. After the butterfly valve is fully opened, the hand wheel should be reversed a little;
2. The connection between the closing part and the valve stem should be firm, and there should be a backstop at the threaded connection;
3. The fasteners used to connect the closing part and the valve stem should withstand the corrosion of the medium and have certain mechanical strength and wear resistance.
Post time: Dec-28-2022
