A valve actuator is a device used to open and close valves in liquid or gas systems. It is responsible for converting external energy (usually electricity) into mechanical motion to operate the valve.

A valve actuator consists of several components including an electric motor, gear system, and control unit. An electric motor provides the power to move the actuator, and a gear system converts the motor's rotary motion into the vertical or rotary motion required to operate the valve. The control device receives input signals, etc. from the control system or operator and transmits them to the operator's movements.

Valve actuators can be divided into two main types: linear and rotary. Linear valve actuators are directly actuated to actuate valves that require linear motion, such as gate valves or ball valves. On the other hand, a rotary valve operates by rotating a valve that requires rotation, such as a butterfly valve or ball valve.