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Five Common Causes and Maintenance Methods of Leakage of Valves - Part 1
Posted: 08/26/2021 23:51:00  Hits: 25
There are many kinds of valves, and valves are indispensable in today's life. In the process of daily use of valves, we can often see leakage faults of valves. Then, what are common causes and maintenance for the leakage of valves? We will give you a detailed introduction as follows:

I. Leakage of the valve body and valve cover

Causes:
1. The casting quality of cast iron is not high. There are defects such as sand holes, loose organization, slag inclusion on the valve body and valve cover body.
2. Cryogenic crack
3. The welding is not good. There are slag inclusions, no welding, stress cracks and other defects.
4. Cast iron valves damaged after being hit by a heavy object.
 
Maintenance methods:
1. Improve the casting quality and carry out the strength test in strict accordance with the regulations before installation.
2. The temperature of the valve is at 0° and below 0°. Heat preservation should be done. Stop the use of the valve and the water should be removed.
3. The welding seam of the valve body and valve cover by welding should be carried out according to the relevant welding operation rules, 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, and it is not allowed to hit cast iron and non-metal valves with hand hammers. The racks are needed for installations of large caliber valves.
 
II. The outer leakage of the packing (The packing accounted for the largest proportion.)

Causes:
1. The selection of packing is wrong. It is not resistant to corrosion of the medium, the use of high pressure or vacuum, high temperature or low temperature of the valve.
2. Packing installation is not correct. The crew coiling joints are bad, tight and loose and there are other defects.
3. The packing has aged and lost its elasticity after the usage life.
4. The valve stem accuracy is not high. There are bending, corrosion, wear and other defects.
5. The number of packing rings is insufficient, and the gland is not compressed.
6. The glands, bolts, and other parts were damaged so as to make the gland unable to be pressed.
7. Improper operation, excessive force, etc.
8. The gland is slanted. The gland and valve stem gap are too small or too large, resulting in stem wear and packing damage.
 
Maintenance methods:
1. The material and type of packing should be selected according to the working conditions.
2. According to the relevant provisions of the correct installation of packing, the packing should be placed and pressed in turn. The joint should be 30℃ or 45℃.
3. The filler with too long service life and those aging and damaged filler should be replaced in time.
4. The valve stem should be straightened and repaired after bending and wearing, and the seriously damaged valve should be replaced in time.
5. The packing should be installed according to the specified number of turns, the gland should be symmetrical and evenly tightened, and the pressing sleeve 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. Operate with normal force at uniform speed except percussive hand-wheel according to the operating procedures.
8. The gland bolts should be tightened evenly and symmetrically. If the gap between gland and valve stem is too small, the gap should be appropriately increased. The gap between the gland and stem is too large, and it should also be replaced.

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