Fisher® 1051 and 1052 spring-return diaphragm rotary actuators operate splined shaft rotary valves, such as eccentric disc (Fisher 8510B and 8560), 8532 and 9500, CV500 and V500 and Vee-Ball™ (V150, V200 and V300) valves. 1051 and 1052 actuators are both suitable for on-off service or for throttling service. The primary difference between these actuators is that the 1052 actuator has a spring adjuster  which means it may be used with or without a positioner, depending on service requirements. The 1051 actuator, in throttling service, is normally equipped with a valve positioner.