Fluorinated thermoplastics such as PTFE, PVDF, PFA, etc. offer significant advantages in terms of chemical resistance and lubricity. You may be familiar with Kynar®, which is the brand name of certain PVDF fluoropolymers manufactured by Arkema. Plast-O-Matic uses 100% Kynar brand PVDF in the manufacture of valve bodies and machined parts. Plast-O-Matic is a licensed reseller of Kynar. All other fluoropolymer items are identified by generic names only.
Many people mistakenly refer to PTFE as “Teflon,” which is actually a registered trademark of DuPont, and is a brand that covers many types of fluoropolymers.
PTFE is practically insoluble and chemically inert to most chemicals and solvents. It is widely used in the handling of high purity deionized water. While PTFE is capable of 500°F (260°C) Plast-O-Matic does not recommend its use in valve designs beyond 300°F (149°C).
The main advantages of PTFE in valve design is that it is ideal for both high purity and highly corrosive applications, because it is virtually impervious to corrosion, and is extremely low in terms of leaching. It is also excellent for valve parts due to its low frictional properties. Its limitations are that it will “cold flow,” i.e., PTFE can be reshaped after contact with other parts. It is also not ideal for higher pressure threaded connections on larger pipe sizes.
PTFE is joined by threading or flanging.
PFA (Perfluoroalkoxy resin)
PFA is a melt processible fluoroplastic equal to PTFE in chemical resistance. It is used for many valve parts such as bellows in solenoid valve, and encapsulation of springs when used as a wetted part. PFA is also used for molded body valves, and although the PTFE valve has a different appearance and translucence, the PTFE valve can be used in place of a PFA valve with no change in chemical resistance. Both materials are equally inert and have the same dielectric constant.
FEP (Flourinated ethylene propylene)
FEP is a relatively soft fluoroplastic, with the same inert, low dielectric, and low friction properties of PTFE and PFA. It does not offer quite the same mechanical properties at elevated temperatures as PTFE and PFA.