The shut-off valve refers to a valve whose closing member moves along the center line of the valve seat. According to this movement form of the valve disc, the change of the valve seat port is proportional to the valve disc stroke. Since the opening or closing stroke of the valve stem of this type of valve is relatively short, and it has a very reliable cut-off function, and because the change of the valve seat port is in direct proportion to the stroke of the valve disc, it is very suitable for flow adjustment. Therefore, this type of valve is very suitable for use as a shut-off or adjustment and throttling.
Once the valve disc of the stop valve is removed from the closed position, there is no longer contact between its valve seat and the sealing surface of the valve disc, so its sealing surface has very little mechanical wear, so its sealing performance is very good.
The disadvantage is that particles in the flowing medium may be trapped between the sealing surfaces. However, if the valve disc is made of a steel ball or a porcelain ball, this problem will be solved. Due to the seat of most Stop Valve
It is easier to repair or replace the valve disc, and it is not necessary to remove the entire valve from the pipeline when repairing or replacing the sealing element. This is very suitable when the valve and the pipeline are welded together.
use.
Since the flow direction of the medium through this type of valve has changed, the minimum flow resistance of the shut-off valve is also higher than that of most other types of valves. However, according to the structure of the valve body and the valve stem
With regard to the layout of the entrance and exit channels, this situation can be improved. At the same time, because the valve disc of the Stop Valve has a small stroke between opening and closing, and the sealing surface can withstand multiple openings and closings, it is very suitable for
Where frequent switching is required.
1. Sealing form of Stop Valve
Plane sealing: both the sealing surface of the stop valve and the valve clack are composed of planes, and the manufacturing process is simple.
Spherical sealing: both the sealing surface of the stop valve and the sealing surface of the disc are made into a conical shape. The sealing is labor-saving and reliable, and the sundries are not easy to fall to the sealing surface.
Cone surface seal: The sealing surface of the Stop Valve is made of a small conical surface and the valve disc is a sphere with high hardness that can be flexibly rotated, which is labor-saving and reliable. Only suitable for smaller diameter valves.
2. Sealing material of Stop Valve
Non-metallic material seal
Soft sealing Stop Valve (PTFE, rubber, nylon, flexible graphite).
Hard seal stop valve (ceramic materials such as alumina and zirconia).
Third, the sealing principle of the Stop Valve
When the medium flows in from below the valve flap, the applied sealing force of the shut-off valve must be equal to or greater than the sum of the necessary specific pressure generated on the sealing surface and the upward force of the medium.
When the medium flows in from above the valve flap, the applied sealing force of the shut-off valve is equal to or greater than the difference between the necessary specific pressure and the medium force generated on the sealing surface.
