The outer seal of the valve generally refers to the seal at the bonnet and the valve stem. The seal at the bonnet refers to the seal between the bonnet and the valve body, which is divided into forced seal and self-tightening seal.

The forced sealing of the valve is to rely on tightening the bonnet bolt to apply a compressive force to the pre-tightened gasket, which is compressed, and the uneven micro-gap on the sealing surface is filled, thus creating an initial condition for preventing medium leakage (sealing surface). form a preload specific pressure). When the medium pressure rises and the valve is operated, the preload specific pressure on the sealing surface drops, and the gasket springs back.
As a high-pressure sealing technology, the self-tightening seal of the valve is often used for high temperature and high pressure large-diameter valves. The self-tightening seal usually used on these valves is a wedge-shaped gasket combined self-tightening sealing structure.