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PTFE Envelope Gaskets
Envelope gaskets utilizing a PTFE jacket and an appropriate filler offer a chemically resistant gasket with low minimum seating stresses, excellent creep resistance, and high deformability.
Fillers such as felted sheet, woven rubberized cloth, corrugated metal and rubber sheets are available. The sandwich constructions with a corrugated metal insert and a soft filler on each side make it possible to use these gaskets successfully at very high pressures.
There are three basic designs of envelopes:
SLIT TYPE
Slit envelopes are sliced from cylinders and split from the outside diameter to within approximately 1/16" of the inside diameter. The bearing surface is determined by the filler dimensions. Clearance is required between the I.D. of the filler and the envelope I.D. The Gasket O.D. normally rests within the bolt hole circle and I.D. is approximately equal to the nominal I.D. of pipe. Available in sizes to a maximum O.D. of 24".
MILLED TYPE
Milled envelopes are machined from cylinder stock. The jacket is machined from the O.D. to within approximately 1/32" its I.D. The jacket's I.D. fits flush with pipe bore and its O.D. nests within the bolts. Available in sizes up to a maximum O.D. of 24". Milled envelopes are more expensive than slit type since considerably more material is lost in machining.
FORMED TAPE TYPE
Large diameter (over 12" N.P.S.) and irregularly shaped envelopes are formed tape and heat sealed to produce a continuous jacket construction.
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