The Type 759 actuator with an integral top-mounted positioner. A pneumatically operated spring opposed diaphragm actuator. Designed to fit the Research Control Valve body-bonnet assembly.
The unit is available in two sizes: one for the 1/4″ valve and another larger version for the 1/2″ through 1″ valves. When equipped with the model TLDA positioner the unit functions as an air-to-close actuator. Extending the stem and closing the valve on an increasing instrument signal. The units design is to retract the stem, opening the valve, on a decreasing or loss of instrument signal.
A force-balance system incorporates the full force of the supply air. This positions the stem precisely, with a high degree of repeatability. This type actuator is useful when the application calls for high positioning accuracy. When greater force is required over the standard actuator such as in the case of high shutoff pressures or excess packing friction.