1.Leakage of stuffing
Causes:
　　 1. Incorrect choice of stuffing: does not resist corrosion of medium, high pressure or vacuum of valve, high or low temperature;
　　 2. Incorrect installation of stuffing: use small accessories instead of big ones, bad spiral contact, upper tight & lower loose;
　　 3. stuffing is beyond the lifetime so it is aged and loses elasticity;
　　 4. The valve stem is not enough in precision and has defects of bending, corrosion or abrasion;
　　 5. The stuffing rings are not enough and the press cover is not tight enough;
　　 6. The press cover, bolt or other parts is damaged so that the cover can not be pressed tight;
　　 7. Improper operation;
　　 8. Oblique press cover, or the space between the press cover and the valve stem is too small or too large so that the valve stem is worn and the stuffing is damaged.
Prevention and solution:
　　 1. Choose the material and type of stuffing according to the working condition;
　　 2. Install stuffing correctly, and the packing set should be put and pressed ring by ring with 30℃ or 45℃ connector;
　　 3. Long-used, aged or damaged stuffing should be replaced in time;
　　 4. Bended or worn valve stem should be corrected and repaired. The seriously damaged should be replaced in time;
　　 5. stuffing should be installed as the set rings and the cover should be pressed evenly with above 5mm space between;
　　 6. Damaged press cover, bolt and other parts should be repaired or replaced in time;
　　 7. All parts, except for impact type hand wheel, should be operated at normal speed;
　　 8. The press cover bolt should be tightened equally. If the space between the press cover and the valve stem is too narrow, it should be enlarged properly.

2. Leakage of seal face
Causes:
　　 1. The seal face is not ground even so that the seal line can not be formed;
　　 2. The connection of the valve stem and the close parts is suspended, skew or worn;
　　 3.The valve stem is bended or incorrectly assembled so that the close parts is skew;
　　 4. Incorrect choice of seal face material or improper choice of valve according to the working condition.
Prevention and solution:
　　 1. Choose correctly the material and type of cushion according to the working condition;
　　 2. Adjust it carefully and operate it stably;
　　 3.Tighten the bolt evenly and equally and use spanner if necessary. There should be certain space between the flange and the screw thread;
　　 4. The cushion should be fixed just in the center without lap joint and double cushions;
　　 5. If the static seal face is corroded, damaged or not processed well, it should be repaired, ground and taken up coloration check;
　　 6. The cushion should be clean and not contact the ground. The seal face should be kerosene.

3. Leakage of seal ring connection
Causes:
　　 1. The seal ring is not rolled closely;
　　 2. The seal ring is not welded well with the body;
　　 3. The screw thread, bolt and press ring connecting the seal ring are loose;
　　 4. The seal ring connection is corroded.
Prevention and solution:
　　 1. For leakage of seal rolling, use adhesive and reroll;
　　 2. The seal ring should be rewelded according to the soldering code;
　　 3. Unpack the bolt and the press ring to clean them and replace damaged parts. For seriously corroded parts, repair it by welding and gluing;
　　 4. If the seal ring connection face is corroded, repair it by grinding and gluing. If it can not be repaired, replace the seal ring.

4. Leakage due to falling off of close parts
Causes
　　 1. Incorrect operation makes the close parts jammed and the connection broken;
　　 2. Close parts are not firm in connection and easy to fall off;
　　 3. Choose incorrectly the connection parts material so that it can not resist the medium and mechanical corrosion.
Prevention and solution:
　　 1. Operate it correctly: do not close the valve with large strength; the valve should not be opened beyond the jammed point; the hand wheel should be reversed a little after the valve is completely open;
　　 2. Connection of the close parts and the valve stem should be firm;
　　 3. Fasteners connecting the close parts and the valve stem should bear medium corrosion and have certain mechanical intensity and wearable performance.

5. Leakage of valve body and cover
Causes
　　 1. Bad cast iron quality causes sand holes, loose tissue, slag inclusion, etc;
　　 2. Crack in bad weather;
　　 3. Bad welding causes slag inclusion, crackle, etc;
　　 4. Cast iron valve is damaged after impact of heavy goods.
　　 Prevention and solution:
　　 1. Improve casting quality and carry out intensity test before installation strictly as stipulated;
　　 2. Preserve heat of 0° and 0° below valves, and eliminate water in unused valves;
　　 3. Line welding of valve body and cover should be processed according to related operation regulation. And flaw and intensity test is needed after welding;
　　 4. Do not put heavy things on the valve. Do not bump the cast iron and nonmetal valve by hand. Use bracket when fixing large-caliber valve.

6. Common malfunction and solution