The Type 754 actuator is a pneumatically operated, spring-opposed diaphragm actuator designed specifically to fit the Research Control Valve body-bonnet assembly. The unit is available in two sizes: one to fit the 1/4" valve and a larger version to fit the 1/2" through 1" valves. It provides smooth linear retraction of the valve stem upon an increasing instrument signal. A decrease in instrument signal causes the stem to extend and close the valve. Downward closing force is generated by the spring, bearing on the diaphragm plate. An increasing pressure in the diaphragm cavity opposes the force of the spring and retracts the stem, opening the valve. The unit is designed to extend the stem, closing the valve, should the instrument signal fail.