The series S&S 867 is a reverse acting, spring opposed, diaphragm actuator with a 4-inch maximum travel. When the signal pressure increases to the lower diaphragm casing, the actuator stem is forced upward, compressing the spring. When the signal pressure is reduced, the spring moves the actuator stem in the downward direction. If the signal pressure should fail, the spring will force the stem in the downward position providing “fail-closed action” for “push down to close” valves.

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