The packing is a necessary valve part for butterfly valve. The packing is elastically deformed by the compression of the packing gland, closely matches the inner wall of the stuffing box and the valve stem, and generates an oil film to contact the valve stem to prevent the leakage of the medium. General speaking, there are several type packings as below :
1. Rubber packing
There are rubber cloth, rubber rod and ring rubber packing, which are used in medium such as ammonia and concentrated sulfuric acid with temperature ≤140 °C.
Polytetrafluoroethylene emulsion impregnated asbestos filler, suitable for highly corrosive media, medium temperature -200 ~ 200 ° C pressure ≤ 35MPa
NFS type PTFE braided packing, suitable for chemicals, medium temperature is -200～260 °C, pressure ≤35MPa
3.Flexible graphite packing.
Flexible graphite filler has the following excellent properties and is now widely used in triple eccentric butterfly valves.
a Unique flexibility and resilience, the cutting filler can be freely bent in the axial direction by more than 90°. It will not leak due to temperature and pressure changes, vibration and other factors during use. It is safe and reliable and is an ideal sealing material.
b Good temperature resistance. Low temperature can be applied to -200 ° C, can be used to 500 ° C in high temperature oxidizing medium, 2000 ° C in non-oxidizing medium, and can maintain excellent sealing.
c Strong corrosion resistance. Good corrosion resistance to acids, bases, organic solvents, organic gases and steam. It does not age, does not deteriorate, and is resistant to corrosion of all media except strong oxidizing medium (nitric acid), fuming sulfuric acid, chromic acid, halogen, etc.
d Low friction coefficient and good self-lubrication.
e Excellent impermeability to gases and liquids.
f Long service life and can be used repeatedly
Zhejiang Zhengfeng Valve