Fisher Emerson control valve

The 657 actuator (figure 1) and the 657‐4 actuator are direct‐acting, spring‐opposed diaphragm actuators. They provide automatic operation of control valve body assemblies. The 657 actuator offers 76 mm (3 inches) maximum actuator travel. The 657‐4 actuator provides 102 mm (4 inches) maximum actuator travel. Both actuators position the valve plug in response to varying pneumatic loading pressure on the actuator diaphragm. Figure 2 shows the operation of these actuators.