The actuator accepts input from the control system and drives the internal component of the valve to vary the flow restriction. The input may be an electrical, pneumatic or mechanical signal. The output most commonly is linear or rotary motion and is rated by force or torque and speed. The connection between the actuator and the valve, consisting of a structural assembly and a coupling device between the actuator drive (output) and the valve stem (input) is a crucial assembly and with the actuator makes up the actuation package.