Valve actuators mount on valves and, in response to a signal, move a valve to a desired position using an outside power source. There are several basic types of valve actuators: manual, electric, pneumatic, and hydraulic. Manual valve actuators do not require an outside power source. They use a handwheel or lever to drive a series of gears whose ratio results in a higher output torque compared to the input (manual) torque. Electric valve actuators use a single-phase or three-phase alternating current (AC) or direct current (DC) motor to drive a combination of gears to generate the desired torque level. Pneumatic valve actuators adjust valve position by converting air pressure into linear or rotary motion. Similarly, electrohydraulic valve actuators and hydraulic valve actuators convert fluid pressure supply into linear or rotary motion.