Seals are used to prevent fluids or solid microparticles from leaking through adjacent joint surface and prevent external impurities such as dust, sediments and moisture from invading. The performance of seals will effect the efficiency and performance of the whole set of machineries. Thus, seals, which are highly required on corrosive-resistance, or to be used above 100℃, are mostly made of PTFE, or PTFE fillers.

Seals are categorized into static seals and dynamic seals. Static seals are equal to fixed seals, e.g. gaskets. Dynamic seals are equal to moving seals, packing is a common material of it. PTFE packing is usually woven by soft thread-formed materials. Its cross-sectional area is of square, rectangle or round strips. Packing is filled into the cavity to realize tight.

The working principle of packing is as follows: Axis’surface is very uneven in the micro, and it can only partly join with packing. The small gap between axis and packing just likes a maze, and the media in maze are intercepted for many times to achieve sealing.

Dynamic seals refer to rotating or reciprocating motion of the seals., which are divided into three forms,i.e. soft seal, ring-types seal and mechanical seal with screw and expansion. Soft seal is generally woven with fiber which is impregnated with PTFE dispersion liquid, and its filler, called as woven packing, has properties of easy installation, softness and common size, but it is difficult to seal gas. Its seal performance can be improved by using PTFE gasket. There are many kinds of ring-typed sealings. According to the materials, they are made of pure PTFE, filled PTFE, and the compounds of PTFE and other high temperature resistant resin, the composites of PTFE and rubber, asbestos, or metal. According to the forms, seals are divided into non-touching seal ( such as seal of a maze) and touching seal (such as piston ring, mechanical seal, “V” type or “O” type ring seal). 

Expansible pump seal with corrugated pipe is composed of static ring and dynamic ring. Static ring is made of corrosive resistant ceramics (prohibited when media is hydrofluoric acid), silicon nitride，or tungsten carbide; And the structure of dynamic ring seal is compact, and it is easy to install. It is resistant to corrosive media, and it has reliable sealing performance. Therefore, it has many advantages such as reducing fluid loss, reducing maintenance, saving machine pump accessories and lowing cost.