The Fisher 667 is a reverse-acting spring-opposed diaphragm actuator that positions the valve plug of sliding-stem control valves in response to pneumatic controller or positioner signals. Air applied to the lower diaphragm casing moves the stem up against the spring; on loss of loading pressure the spring drives the stem fully down, giving fail-closed action on push-down-to-close valves and fail-open action on push-down-to-open valves. Available in sizes 30 through 100 and 76, plus the 667-4 with 4 in (102 mm) travel in sizes 70 and 87. Standard operating pressure range 3 to 15 psig or 6 to 30 psig (667-4: 3 to 27 psig; size 76: 6 to 30 or 0 to 45 psig). Molded diaphragm in a deep casing for linear response, steel diaphragm casing (sizes 30-87), nitrile elastomers for -40 to 180 °F or silicone diaphragm to 300 °F, and cold service construction to -58 °F. Split-block stem connection, stainless steel travel indicator, and optional top- or side-mounted handwheels and adjustable travel stops. SIL 3 capable, certified by exida.
