Leakage of valve body and bonnet:

1. Explosion-proof electric valve cast iron castings casting quality is not high, valve body and bonnet body has sand holes, loose tissue, slag and other defects

2. Freezing day crack;

3. Poor welding, there are slag, not welded, stress cracks and other defects;

4. Cast iron valve damaged by heavy impact.

Second, the leakage of the packing (valve leakage, the proportion of filler is the largest)

1. Filler selection is not, not resistant to corrosion of the medium, the valve is not high pressure or vacuum, high-temperature or low-temperature use;

2. Filler installation is not correct, there is a small generation of large, spiral wound joints bad, tighten down loose and other defects;

3. Filler over the period of use, aging, loss of elasticity

4. Valve stem accuracy is not high, there are bending, corrosion, wear and other defects

5. Insufficient number of filler rings, the gland does not press tight;

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

7. Improper operation, excessive force and so on;

8. Gland askew, gland and stem gap between too small or too large, resulting in stem wear, filler damage.

Leakage of sealing surface

1, sealing surface grinding uneven, can not form a dense line;

2, the valve stem and closes the connection place pinion is vacant, is not positive or wears;

3, valve stem bending or assembly is not, so that the closure of the parts askew or not;

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

Iv. leakage at the connection of the seal ring

1, seal ring rolling pressure is not strict

2, sealing ring and the main body welding, poor surfacing quality;

3, sealing ring connecting thread, screw, pressure ring loose;

4, sealing ring connection and corrosion.

The closing piece falls off to produce the leakage:

1, the operation of the bad, so that the closure of the die or more than the dead point, the junction damage fracture;

2, close the connection is not strong, slacken off and fall off;

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