Another simple actuator is the diaphragm with spring-return which is fail-safe because the spring moves the valve to the fail-safe position when the control signal fails.
The disadvantage of this actuator is that it is limited to small valves in low-pressure service. It can actuate up to a three-inch ANSI Class 600, four-inch ANSI Class 300, or six-inch ANSI Class 150 ball valve, and up to a six-inch ANSI Class 600, an eight-inch ANSI Class 300, or a ten-inch ANSI Class 150 high-performance butterfly valve.
Do not install diaphragm actuators without fireproofing in fire hazardous areas. The yokes are often cast iron which, in a fire, may break when hit by a stream of cold water, thus causing the valve to fail open.
Often, both the diaphragm actuator and valve are supplied by the same manufacturer.