Knife gate valve failure and maintenance method

by:Lianke Valve     2022-08-23
Listed below are some common faults and troubleshooting methods for knife gate valves. 1. Leakage of closing parts of knife gate valve: Usually, the leakage of stuffing box is called external leakage, and the leakage of closing parts is called internal leakage. The leakage of closing parts can be divided into two categories; one is the leakage of the sealing surface; the other is the leakage of the root of the seal. The reasons for the leakage are: 1. The sealing surface of the knife gate valve is not well ground; 2. The sealing ring is not tightly matched with the valve seat and valve office; 3. The connection between the valve office and the valve stem is not reliable; 4. The valve stem is bent and twisted. Make the upper and lower closing parts misaligned: 5. The closing is too fast, the sealing surface is not in good contact or has long been damaged; 6. The material is improperly selected and cannot withstand the corrosion of the medium: 7. The globe valve and gate valve are used for adjustment, and the sealing surface cannot withstand Resist the impact of high-speed flowing media; 8. Some media gradually cool down after the valve is closed, causing fine seams on the sealing surface and erosion; 10. The valve core cannot be closed tightly due to the insertion of impurities such as welding slag, rust, dust, etc., or the falling off of mechanical parts in the production system to block the valve core. 2. Knife gate valve packing box leakage: 1. The corrosiveness, temperature and pressure of the packing and the working medium are not compatible; 2. The filling method is incorrect, especially when the whole packing is screwed into the spare, it is most likely to cause leakage; 3. The valve Insufficient rod machining accuracy or surface finish, or ovality, or nicks; 4. The valve stem has pitted corrosion, or rusted due to lack of protection in the open air; 5. The valve stem is bent; 6. The packing has been used for too long and has aged . 7. The operation is too violent. 3. Failure to lift the valve stem of the knife gate valve: 1. The thread is damaged due to excessive operation; 2. Lack of lubricant or lubricant failure; 3. The valve stem is bent and twisted; 4. The surface finish is not enough; Too tight; 6. The valve stem nut is inclined; 7. Improper material selection; for example, the valve stem and the valve stem nut are made of the same material, which is easy to bite; ); 9. The open-air valve lacks protection, and the valve stem thread is full of dust and sand, or is rusted by rain, dew, frost and snow. 4. Others: 1. Valve body cracking: generally caused by freezing. When the weather is cold, the knife gate valve should have thermal insulation and heat tracing measures. 2. Damage to the handwheel: caused by impact or strong operation of the long lever. As long as the operator or other relevant personnel pay attention, it can be avoided. 3. The packing gland is broken: the force when pressing the packing is uneven, or the gland is defective. Compress the packing, rotate the screw symmetrically, and do not skew. When manufacturing, not only should pay attention to large and key parts, but also pay attention to secondary parts such as glands, otherwise it will affect the use. 4. Failure of the connection between the valve stem and the gate: The knife gate valve adopts many forms of connection between the rectangular head of the valve stem and the T-shaped groove of the gate, and the T-shaped groove is sometimes not processed, so the rectangular head of the valve stem wears quickly. Mainly from the manufacturing aspect to solve. However, the user can also perform supplementary processing on the T-row groove, so that it has a certain smoothness.
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