36" soft seated butterfly valves. When the valves were disigned for vent gas compressor suction valves the styrene content was not taken into consideration so the TFE seat ring with viton o-ring are not compatable. Polymer builds up behind the seat ring and also causes swelling to the viton backup o-ring. Graphite is normally only attacked by very strong oxidizers. Why don't you replace the viton O-Ring with another elastomer? I'm surprised that Viton is attacked: Usually amines and acetate radicals attack viton. Water swells Viton a little. Nitrile is resistant to most HCs but limited to around 180F, Silicone is pretty easy to get and operates at higher temps--susceptible to some solvents, tho'. Or if you have significant funding there is Kalrez. It still won't be as expensive, though, as a new valve. If you can use a Fluorocarbon seal ring you can use PTFE packing. Usually the first ring in a Graphite packing set is a braided junk ring-your monomer is probably building up in this porous ring and causing you the problems. At least TFE is not porous and it's famous for being slippery.

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