A valve actuator is the device that “actuates,” or moves, a valve open or closed. It attaches to and works in conjunction with two parts: the valve body and the valve pilot.
WHAT ARE THE TYPES OF VALVE ACTUATORS?
Two common types of valve actuators include pneumatic and electric.
How Does a pneumatic Valve Actuator Work?
One of the most common actuators is a pneumatic actuator, like the one on the standard Kimray High Pressure Control Valve.
These actuators are typically comprised of an adjusting screw, breather plug, bonnet, spring, diaphragm assembly, and stem.
- The adjusting screw puts pre-load on the spring to engage the valve in its fail position.
- Without a pneumatic signal on the diaphragm, the valve will remain in this position.
- The diaphragm is the key component of the pneumatic actuator. This flexible and air-tight piece moves with the spring yet holds in air pressure.
- The breather plug allows the non-energized side of the diaphragm to move freely without getting air locked.
This assembly—sometimes referred to as a valve’s “Topworks”—is bolted directly on top of the valve body.
The diaphragm pressurizes when the actuator receives a pneumatic signal from a pressure pilot. In a back pressure application, the pilot on this senses upstream pressure. Then it sends an output signal (gas) through tubing into the actuator of the valve.
As a result, the actuator actuates, driving the valve open or closed, depending on its configuration. (Note: The action in this particular valve can be reversed.)
HOW DOES AN ELECTRIC CONTROL VALVE ACTUATOR WORK?
An increasingly common method of actuation is an electric actuator, like the Tritex II.
An electric actuator is typically comprised of a control board, drive motor, and adapter.
- The control board is the brain of the electric actuator. This is where you will terminate power and the signals from the controller.
- When energized, the drive motor will engage and move the valve open or closed, depending on the signal.
Whereas the signal for a pneumatic actuator comes from a pressure pilot, the signal for an electric actuator comes form another outside source, like an electric pilot, Programmable Logic Controller (PLC), or Remote Terminal Unit (RTU).
In the case of an electric actuator on a High Pressure Control Valve in a back pressure application, the electric pilot receives an analog 4-20mA signal from a sensor, which represents a process condition. The electric pilot conditions this signal and sends a corresponding signal (4-20mA) to the electric actuator of the valve.
As a result, the actuator actuates, driving the valve open or closed, depending on its configuration.
How Do I Choose a Valve Actuator?
There are three primary factors to consider when selecting an actuator: Emissions, Automation Capabilities, and Cost.
As environmental regulations tighten, electric actuators are becoming more popular because they do not require the use of supply gas and therefore do not release emissions. If you want to reduce emissions with pneumatic actuators, you can power your pneumatics with compressed air or install a vapor recovery unit.
Another factor to consider is automation capabilities. A significant benefit to using electric actuation is the ability to automate valve functions. Simply put, automation gives you the ability to monitor and control your valves offsite. With a pneumatic actuator, you can do this by using an I/P valve controller, which converts an electric signal to pneumatic.
Cost is the third factor to consider. The upfront cost of a pneumatic actuator will typically be less than an electric actuator. However, when considering emissions management and the efficiency gains automation provides, electric actuators provide significant value.
One other benefit of electric actuation which is sometimes overlooked is worker safety. Workplace injuries can be stressful and costly. Because electric actuation allows you to monitor and control production remotely, workers make fewer trips to the field. This means there are fewer opportunities for injuries to occur.
To speak with an expert about setting up your actuator or other control equipment, reach out to your local Kimray store or authorized distributor.