Looking for a recommendation for butterfly valves 10 -12" size for use in a SYLTHERM SERVICE low temperature application -112C to plus 230C. rubber seated butterfly valves have usually single- or double-eccentric design and are usually used in water services (or similar), while triple-eccentric ones are usually metal seated. "Metal seated", however, does not exclude the presence of "soft" parts where graphite (or PTFE, depending on service conditions) is present: spiral wound gaskets, stem packing and seal. Many triple-offset metal-to-metal valves (like Vanessa Series 30,000 by Tyco, for example) have a seal ring mounted on the disc and the seat on the body, hard faced with Stellite, Inconel, Ultimet, etc.; the seal ring is usually of a lamellar type, i.e. made of alternate lamellas of metal and graphite (or PTFE). Depending on the service conditions (high temperature, solid particles, etc.) a "solid", all-metal seal ring is also used. Both can achieve very good sealing performances, such as "Class VI" for control valves or "Zero Leakage"

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