There are many types of high-pressure seals. According to its working principle, it is divided into two categories: forced seal and self-tight seal. Forced sealing is based on the pretightening force of the coupling (bolt) to ensure a certain contact pressure between the top cover of the pressure vessel, the sealing element and the end of the cylinder in order to achieve the purpose of sealing. The self-tightening seal is such that as the operating pressure in the pressure vessel increases, the contact pressure between the sealing element and the top cover and the end of the cylindrical body also increases, thereby achieving a sealing effect. Self-tightening is characterized by the higher pressure, the greater the pressing force of the sealing element on the contact surface, the better the sealing performance, and the sealing is still reliable when the operating conditions fluctuate. However, the structure is more complicated and manufacturing is more difficult. Self-tightening seals can also be divided into axial self-tightening seals and radial self-tightening seals according to the deformation of the sealing element.

According to the performance of the sealing material, the high-pressure sealing can be further divided into a plastic sealing that causes the plastic deformation of the sealing element, so that the sealing element is elastically deformed and elastically sealed.

At present, the commonly used seal types of pressure vessels are as follows:

1) Forced seal with flat pad seal, Qaryli seal and octagonal pad seal;

2) Semi-self-tight seal with double cone seal;

3) Self-tight sealing with wedge seal, five German seal, hollow metal O-ring seal, C-ring seal, B-ring seal, triangle pad seal, octagonal mat seal, flat pad self-tight seal and rubber O-ring seal, etc.