Aside from the control system itself, the most comprehensively discussed component of any process system is the valve. Whether the application is a simple open/closed manual valve, severe service flow control valve or critical isolation valve, engineers and suppliers spend hours discussing, specifying and designing valve packages that can withstand a multitude of factors for operation. One component of that package that is equally critical, yet sometimes overlooked, is the actuator.

The decision to automate a valve requires several considerations. Below are some factors, but certainly not all, that an engineer must consider when choosing an actuator:

What are we trying to accomplish in the system with this valve? Is this a flow control loop, an isolation valve, pump protection? What are the factors in the process—such as pressure, temperature and flow rates—required for the application? While these are typically considered when specifying a valve, they are still critical to understanding how they can impact the performance of an actuator.

For example, if an actuator is undersized, or not specified correctly to the valve and process variables, it may not have the proper amount of force to fully close the valve, resulting in unreliable process control. A typical given multiple of the valve’s operating torques to ensure proper operation of the actuator is 25%. This difference between valve torque requirement and the output capability of the actuator ensures the unit will continue to function well and provide a measure of protection against process changes.

Users should consider how the control system will interact with the actuator. They should also determine if the actuator will utilize air or electricity to operate. Will there be a control signal in the form of a relay output and solenoid or 4-20 milliamp (mA) signal to a controller? What feedback requirements are required from the actuator? For example, a requirement could be a feedback signal in the form of 0-10 volts to verify valve position back to the programmable logic controller (PLC).

Another negative result of choosing the wrong actuator is the loss of repeatability in control. The wrong actuator can work in an application for a short time but, if this valve were to malfunction, there may be an impact on the process that could affect the users or possibly the environment. Users should examine what action the unit needs to take in the event of loss of control or power. Understanding how the valve, actuator and any controls work together is critical to success. The various actuation technologies and the benefits they provide are critical to success. Furthermore, look into any legal requirements, codes or standards that demand a specific level of performance. The regulations and certifications may vary across industries and applications.

While this is not the only deciding factor to make the most technical and economic choice, every engineer must consider the overall project budget when making their actuator selection. While there is the consideration of the initial investment cost, there is also the need to operate and maintain an asset over its life cycle. Depending on the air or electric consumption or cost to maintain and repair, a lower initial cost benefit may be lost over time when trying to resolve issues with a troubled unit.

Every actuator has to perform, at minimum, the following functional purposes:

Engineers are looking for suppliers who provide technologies and equipment that not only serve the basic purpose of process control in their facilities but also more features and benefits that maximize productivity, increase results and solve problems that contribute to lost uptime and profitability.

Shane McDaniel is the business development manager for actuation products at Asahi/America, Inc. Contact McDaniel at 281-505-7884 or smcdaniel@asahi-america.com. For more information, visit www.asahi-america.com.