Electric actuators are essential components in many industries and daily life performing all sorts of jobs that require an automated movement action, this can be push-pull or rotary turn, but in a more specific thought towards the valve industry they are used when an automated or remote action is required to open and close a valve.
This article provides a comprehensive overview of electric actuators. Covering their principles, components, operation and how you can choose the right electric actuator for your application.
Principles Of Electric Actuators
In the world of valves nearly all actuators start with a rotary motion that is created through an electrical motor which is connected to a gear mechanism for the final drive output. Also incorporated into the actuator will be a set of controls that will manage the movement, this can be anything from simple switches to turn the motor on and off or very complex electronic systems that can give precise modulating movement or sophisticated communications with feedback to a site’s computerised PLC system.
What Are The Components & Features Of An Electric Actuator
Electric Motor
Valve operating actuators use an electric motor to create motion, there are various types of motor, but they all work on the same principle of using electrical current to generate magnetic fields which in turn interacts with other magnetic components to produce the mechanical rotary motion. The choice of motor depends on factors such as torque output, power supply availability and working environment. Common motor types include:
- Brushed DC Motors
- Double Wound capacitor run AC motor
- squirrel cage induction 3PH motor
Gearing Mechanisms
As the output from the electric motor rotates fast but with relatively little torque the actuator incorporates a gear system to amplify the motor’s power and control the actuator’s speed and force. The more complex type of actuator allows for assembly with differing gear ratios for achieving the desired output, whether it’s high-speed motion or high-torque movement, whereas the commodity range of actuators will have a standard fixed set of gears per individual model size.
Housing
The workings of an electric actuator are held together and enclosed with a housing that not only protects the inner components from the outer environment but also protects the user from the electrical and mechanical dangers and the environment from any sparks or sources of ignition that can occur with an electrical equipment, especially important in hazardous areas where the housing may need to be explosion proof.
Mount & Drive Connection
As the actuator is designed to do work, to turn a valve shaft, it must be mounted securely so it is held steadfast, this is normally done with a set of fixing points on the base of the housing and in modern actuators this will comply to the international standard bolting arrangement ISO-5211. The drive will come from the output shaft of the internal gearing and protrudes through the housing, this will either fix directly to the valve shaft or via ‘mount kit’ assembly that links valve to actuator.
Drive Output
Depending on the valve type will determine what type of drive is required from the actuator, for example ball and butterfly valves will only require a ¼ turn of motion whereas gate and globe valves will want multiple rotations of drive to full open and close the valve.
Controls
The actuator will work autonomously on the command from the workplace control station but does require additional devices within the actuator housing to complete the system, the most common of these being a pair of limit switches that turns power on / off at the end of the operating stroke. Other types of control such as 4-20mA positioners or HART communication can be fitted to enable more elaborate features like modulating control or two-way feedback communication. On occasions there are requirements for an actuator to be operated locally, some actuators come fitted with override handwheels to accommodate manual control at the valve, or the actuator could be fitted with an external selector switch to move the operation into differing operating modes, Automatic (remote control); Manual (local control); off (isolated); when in the Manual (local) position a second selector switch will allow open / closed commands.
Fail Safe
Most electric actuators will stop working on the loss of electrical power supply but for some safety critical applications this is not acceptable, in an emergency some valves may need to close to prevent further damage or danger occurring. Specially designed actuators can be fitted with spring modules or battery backup packs that will take over during power loss to move the valve to a designated safe position.
Wiring
Depending on the type of controls will depend how complex the wiring will become, basic on/off actuators can use a simple 2 or 3 wire system whereas an actuator with lots of extra features like communication, feedback devices, heaters can have a large multi cable junction terminal block that requires a logic wiring diagram when it comes to cabling up. All electrical work should be carried out by a skilled person but extra consideration should be given when it comes to cabling actuators that are being used within a hazardous environment.
Additional Accessories
Depending on the final application or the clients requirements there are many additional accessories that can be fitted with the actuator housing that will perform jobs such as feedback or enhanced working benefits. The most common of these are:
- Modulating Control 4-20mA positioning
- Feedback Limit Switches
- Feedback Potentiometer
- Feedback 4-20mA Signal (return)
- Motor Relay
- Heater, anti-condensation
- Motor brake
- Motor Contactors
Choosing The Right Electric Actuator for Your Application
It’s crucial to understand and bring all the variables involved in electric actuators to the selection process when specifying an actuator to ensure the unit is fully defined and meets the applications specific requirements. By carefully assessing these factors, AC Valve Alliance can help guide you through the process and confidently select the electric actuator that best suits your application’s needs, ensuring optimal performance, efficiency and an actuator that will safely do the job.
AC Valve Alliance Electric Actuators
AC Valve Alliance have an inventory of Bernard Controls electric actuators, coupled with an ACE Partner status with AUMA. Both establishing a robust presence in the electric automation industry. Additionally, our enduring partnership with Dresser RCS and Asahi further enhances our product portfolio and offerings in this sector. Contact us today to find your ideal electric actuator.
