ICI's Actuator & Valve Industry Blog

How does an electric actuator work?

Posted on Mon, Feb 10, 2014

How does an electric actuator workIf you need an answer to the following questions, you are looking in the right place:

  • What are the main components of an electric actuator?
  • How is a two-position electric actuator wired?
  • Open, Close...  How does it really work?
  • What if the valve is not completely opened or closed?
  • Do you need to apply constant power to an electric actuator?
  • Do you really need a start capacitor and a brake on an electric actuator?

Video

Because videos are better than a million words:

Summary

Now, we all know that in the great art of communication, it is best to first introduce what we are going to be talking about, then talk about it and to finish, summarize what we just talked about. So here is the recap:
 

What are the main components of an electric actuator?

An electric actuator is made of many parts but few of them are critical and it can be useful to understand how they play in the whole actuator.

A motor can be any known voltage used over the world and in different industries. Voltages most commonly availables are: 115 VAC, 24 VAC, 24 VDC, 12 VDC, 208 VAC or 230 VAC. These are all single phase motors @ 60 Hz but 3 phase motors can also be used like 230 VAC or 460 VAC.

A brake is mounted on top of the motor to prevent the media from forcing on the valve and opening it unwantedly.

A motor start capacitor gives the motor the necessary force to start.

Limit switches are used to provide the necessary number of electrical contacts in the open, close or intermediate position. Standard electric actuators have two SPDT limit switches, one for the open position and one for the closed position to control rotary travel. Cams, slided on the shaft, activate the switches when reaching the desired position. 

A terminal strip to supply power to the different electrical components.

How is a two-position electric actuator wired?

Terminal strip has several pins to connect the wires. Pin 1 is usually the neutral line. Pins 2 & 3 are is the hot line for the open and close position. This hot line is split by a control switch or any kind of relay.

Open, Close... How does it really work?

All actuators leaving Indelac facility are always in the open position. 

What if the valve is not completly opened or closed?

Cams can be adjusted by loosening the set screw and rotating the cams left or right into the desired position. The goal is to make the actuator rotate a little bit further to fully close or open the valve. Repeat the operation in both open and close positions until satisfaction. 

Do you need to apply constant power to an electric actuator?

Yes, there is always power to either pin 1 and 2 or pin 1 and 3. The limit switches are cutting power to the motor when the actuator has reach the deisred position (open or close).

Do you really need a start capacitor and a brake on an electric actuator?

The motor start capacitor is always needed to give enough power to the motor to start.

The brake is being energized in the close position to hold the motor in position. If no brake is mounted, the risk is that the force of media inside the pipe pushes the valve and open it slightly. The actuator will detect the valve being open and will rotate again to full close position. Repeating this action over and over, as the media pushes the valve back open. Over time, this will damage the motor and the actuator (see picture below for more info).

Why Utilize a Power Off Brake