PFA
PFA (Perfluoroalkoxy) was developed in order to achieve a true melt-processable fluoropolymer. Its characteristics are such that in service it can be considered as interchangeable with PTFE in terms of its chemical service and temperature and pressure duty. It has the highest permeation performance of the fluoropolymers, exceeding that even of paste extruded PTFE. It also provides the smoothest and least wettable finish of all of the Fluoropolymers. Unfortunately the trade-off is cost, the material being more expensive than PTFE. CRP uses PFA in the production of most of its lined fittings and the Flowserve range of Atomac and Durco chemical valves are available lined in PFA.
FEP
FEP (Fluorinated Ethylene Propylene) is another melt-processable Fluoropolymer. It does not have the almost universal chemical resistance of PTFE and PFA and its maximum operating temperature in service is 150oC. CRP uses the material occasionally for the manufacture of “sheet lined products”. This is essentially a lining made up of sheet and tube elements of FEP welded together in situ. Sheet lining allows one to line complex articles without the use of expensive moulding tools, to cope with the inevitable tolerance errors of welded fabricated steelwork and with the use of bonded linings to provide a degree of vacuum performance. Where the chemical performance and temperature duty are not an issue, the material provides a less expensive alternative to PFA. Flowserve manufacture the Atomac range of lined valve in FEP.