These gaskets incorporate a silicone o-ring to regulate compression in the innermost diameter of the gasket, and also allow for flange and mounting irregularities. The silicone has a large temperature range where it remains pliable, so it is able to help support the PTFE sleeve in a wide range of services. The higher durometer non-asbestos filler means the silicone o-ring portion of the gasket will be placed under compression but not flattened completely, allowing it to function as a good base between the valve and piping flanges and the PTFE sleeve. Testing has shown that the silicone o-ring backed version of the gaskets has a higher sealability, and is more forgiving than gaskets with only the standard non-asbestos backing.
N/ATo achieve maximum sealing capability, proper installation procedure must be followed. PTFE gaskets require re-torque after initial installation. See maintenance manual MM-FG001.