1. The static seal

The "O" rubber ring is the most commonly used sealing ring in detachable connection. It is usually placed in the flanges, and when the two flanges are evenly clamped with the screw, the "O" rubber ring is crushed and the gap is blocked. It has the function of static sealing, and its sealing forms include plane groove, right angle surface matching planting, plane matching plane, wedge matching groove, etc. But no matter what form, its flange airtight cover should be smooth, it can not have the mark on the seal surface to ensure the sealing pressure. For detachable vacuum gauge joints, it is also a common static seal structure. For liquid nitrogen, especially liquid helium, it is often used for sealing rings with gold or ockline.

2. The dynamic seal

In the low temperature experiments, we often will encounter butterfly valve rotating shaft rotation, the rotation of the needle valve, movable liquid level gauge rod and vacuum pump rotation axis movement, there is a leakage problem. The seals of these moving parts are called dynamic seals.

The dynamic seal can be divided into three kinds of sealing methods:

1) it uses the "O" ring to seal the action. In low vacuum conditions, the rubber trap with small aperture ratio shaft is used on the shaft or pole, and then it relies on the compression nut and metal gasket to make it tight and shaft contact and seal.

2) Wilson seal, which is better than the round rubber ring seal;

3) metal bellows seal, it is dependent on the elastic of the metal hose, and the crankcase can be sealed.

In recent years, the sealing of vacuum rotating shaft in foreign countries has been sealed with magnetic liquid, which is characterized by high speed rotation and small leakage rate, which is commonly used in ultra-high vacuum system.

3. The electric lead sealing

Some of the wires in the cryogenic devices, such as power lines, temperature measurement, liquid measuring surface, magnet leads, etc. They easily destroy the air tightness of the whole device.