Processing problems of valve contact seals: In theory, as long as the two sealing faces are close to each other and the gap is smaller than the diameter of the medium molecule, the medium can be prevented from passing through to achieve the purpose of sealing. In fact, no matter what kind of processing method, the real ideal surface can not be obtained. There are always micro-bumpy "peaks" and "valleys" on the actual sealing surface, and there are also macroscopic dimensional and shape positions and other errors, manual valves. The two sealing faces do not achieve the desired perfect fit). Therefore, when the valve is manufactured and processed, the processing precision and the surface roughness of the sealing surface are improved, and the microscopic gap between the sealing faces is reduced, thereby facilitating the sealing.

Loading problem of valve contact seal: Another method to ensure valve sealing is to apply external load force to the sealing surface when the valve is closed, or to use the force of the medium on the sealing surface to make the sealing surface of the contact surface microscopically convex. In the "peak" part, elastic or local plastic deformation occurs, so that the microscopic contact area is enlarged, and the gap is reduced. At this time, however, the contact pressure of the sealing surface cannot be increased infinitely because the contact pressure exceeds the safety strength of the material, and the sealing The surface is easy to cause seizure or scratching, and even the overall plastic deformation, resulting in seal failure, and the valve is the opening and closing dynamic seal, requiring the seal to be repeated many times in the service life.

When the contact pressure is increased, the force of the medium on the sealing surface is limited, meaning that the external load force required to open and close the valve will increase, and almost all parts of the valve, especially the transmission parts (such as valve stems, valves) The force of the rod nut, hand wheel or driving device will increase, the safety and reliability will be reduced, and the opening and closing parts such as the ram will also have macroscopic deformation and affect the sealing surface, so that the valve strength design needs Additional costs, such as increasing the stem diameter and increasing the thickness of the ram. Therefore, under the premise of ensuring the valve seal, the external load force required to open and close the valve should be minimized.