Improvement in Valve Stem Sealing of Slab Gate Valves

The leakage caused by the failure of the sealing of the slab gate valve is one of the problems that affect its service life and promotion and application, especially for the working conditions requiring zero leakage, which limits its scope of use.


 

The analysis of the problem 

The valve stem seal is achieved by using the extrusion between the packing and the valve stem to make the packing clamp the valve stem and reduce the gap between the packing and the valve stem. When the valve is used for too long, the properties of the packing change, the packing wears or the pre-tightening force of the packing is insufficient, so the gap between the packing and the valve stem increases, which will affect the sealing effect of the stuffing box and cause external leakage. Here, if the method of increasing the number of packing layers and improving the surface roughness and straightness of the valve stem cannot completely solve the problem of external leakage, the structure of the stuffing box should also be optimized.

Improvement in the structure of sealing

Aiming at the leakage of the stem seal of the slab gate valve, the sealing structure has been improved. The structure has multi-layer sealing, one layer is the O-ring seal, and the other is the packing seal. The O-ring selects the appropriate interference amount according to the pressure rating of the valve, or adopts a one-way retaining ring, which can meet the general requirements for sealing.

Precautions

1. The improved valve stem seal has a multi-stage series structure, and the sealing packing should be made of materials with excellent elasticity.

2. Each layer of packing should be pressed well to compensate for the wear of the valve stem on the packing. Tests have shown that the packing can be maintained close to the limit life of the packing once compacted, which is more reliable than multiple compacted packings.

3. If the stem seal leaks, the packing should be replaced immediately, and there is no need to compress it many times. For working conditions that require zero leakage, the packing should be replaced regularly in strict accordance with the test life of the packing, and it should not be compressed many times.

Field use proves that the slab gate valve with improved sealing structure has a longer service life, more convenient operation, reliable performance and simple structure.