Belimo Controls SM230A Actuator 20 Nm Open Close, 150 s, 95 deg rotation, 3-point control, IP54, motorised damper actuator, HVAC actuator

An actuator is the motorised head that opens, closes or positions a valve when the heating or building controls signal it. This category covers zone valve and boiler diverter valve heads, underfloor heating manifold actuators, rotary actuators for mixing valves and dampers, linear actuators for control valves, and gas valve actuators.

Matching the actuator

• Valve and fitting: actuators are made for particular valve bodies, or fit others through an adapter kit. Check the make and model of the valve, or of the boiler for a diverter valve head.
• Movement: rotary actuators turn the spindle of a mixing, ball or butterfly valve, while linear actuators push and pull the stem of a seat or globe valve.
• Supply voltage: most run on 24V or 230V, and the actuator must match the controls it is wired to.
• Torque and running time: ratings are given in newton metres and seconds; compare them with the original.

Control signals

Two-point actuators simply open or close, which suits diverting duties. Three-point, or floating, actuators drive the valve open or closed in stages and suit mixing duties. Proportional or modulating actuators follow a variable voltage or current signal, such as 0 to 10V, so the valve can sit at any position for mixing and flow control. A replacement must accept the controller's signal type.

Safety

Isolate the electrical supply before work and follow the wiring diagram. In England, a new circuit is notifiable under Part P of the Building Regulations and must be done by a registered competent person or notified to building control. Work on gas pipework, appliances and their gas parts must only be carried out by a Gas Safe registered engineer, and that includes gas valve actuators.

For the valves themselves, see central heating valves, or browse heating controls.