A Practical Guide to Electric and Pneumatic Actuators - Which to Choose?
While electric and pneumatic actuators have several unique advantages and are favored in different applications, using the wrong actuator in your application can have serious consequences. However, choosing between them can be very confusing. This article explores the working principles and differences between pneumatic and electric actuators, then provides a comparative analysis of their characteristics to help you choose the right actuator for your application.
A valve actuator is an automated device used to remotely control a valve without human intervention. These devices generate movements to control valves based on the signals they receive. The actuator is mounted on the valve to be controlled, replacing the manual lever. The installation features for connecting the valve to the actuator vary by actuator model.
Valve actuators are broadly classified according to how they generate the torque or force required to open the valve. Based on this classification, the two most popular types of actuators are electric and pneumatic. Electric valve actuators use electricity to generate the required motion, while pneumatic actuators utilize a compressed air system. The third type of valve actuator exists, called hydraulic actuators, but these are less common.
Electric actuators convert electrical energy into force to open or close a valve. These devices can operate on AC or DC power. An electric valve actuator may have an electric motor that produces a rotational motion that turns the valve. This type of actuator is used for quarter-turn valves and requires a 90° turn to open or close, and is called a quarter-turn actuator. Examples of quarter-turn actuators are ball and butterfly valve actuators.
Another type of electric actuator that is widely used in piping and fluid control systems is the electromagnetic actuator. These devices are usually integrated with the valve to form a unit.
Pneumatic actuators utilize a pneumatic system (controlled compressed air system) to generate the force required to operate the valve. These actuators may have pistons or diaphragms controlled by compressed air. The more common varieties with pistons contain a piston housed in a chamber. Pneumatic actuators can be single-acting or double-acting. Single-acting actuators, commonly referred to as spring-return actuators, have a loaded spring on one side of the piston that holds the valve in its natural position. To open or close the valve, pressurized air is supplied on the other side of the piston, and the air pressure overcomes the force of the spring.
On the other hand, in a double-acting actuator, the air is supplied to both sides of the piston. The pressure difference between the two sides keeps the valve in the desired position. Pneumatic actuators typically produce linear motion. However, in actuators such as butterfly valve actuators (which need to generate rotational motion), motion conversion mechanisms (e.g rack and pinion, and fork mechanisms) are used.
Choose between electric and pneumatic actuators
Both electric and pneumatic valve actuators have specific advantages in different applications. To select the right actuator for your application, certain factors and characteristics of these actuators must be analyzed. Some of these factors and characteristics are discussed below.
Accuracy needs to be considered for valves that need to operate in a partially open or closed position to allow an exact amount of media to flow through. Both electric and pneumatic actuators provide precise control. However, when relying on pneumatic actuation, it may be necessary to include an electro-pneumatic positioner as an accessory on pneumatically operated equipment such as control valves to achieve the high-precision control required in applications such as chemical production.
2. Force range
Compared to electric actuators, pneumatic actuators provide significantly higher force/torque per unit side. For applications involving large valves or valves with high working pressures, pneumatic actuators are a better choice.
In specific applications such as flood protection, drive speed is a critical consideration. As with precision, both electric and pneumatic actuators can be fast. However, pneumatic actuators react faster and have high-duty cycles. In addition, the operating speed of the pneumatic actuator is adjustable.
Pneumatic actuators have fewer components. As such, they are easier to maintain and have a longer lifespan than electric actuators, which have multiple parts that may require regular maintenance. However, while the actuator unit may not require maintenance, other components such as air compressors and FRLs (filters, regulators, and lubricators) may require more frequent maintenance
Pneumatic valve actuators are simpler in design than electric actuators, so these actuators cost less than electric actuators. However, the overall cost of the pneumatic drive system increases when the cost of the supporting pneumatic system is considered. Significant cost reductions can be achieved by setting up multiple actuators using the same pressurized air supply system.
In applications where actuator failure can have serious consequences, actuators need to have fail-safe mechanisms. It is easier and less expensive to install fail-safe devices in pneumatic actuators. Spring return pneumatic valve actuators have a natural fail-safe mechanism because in the event of a fault, the force of the spring automatically returns the valve to its natural position.
7. Hazardous situations
Electric actuators often have delicate components that may not function properly in hazardous conditions. Additionally, these actuators require extensive certification to be considered suitable for certain environments. Electric actuators require a high level of protection against high temperature and pressure, dust, and moisture. On the other hand, pneumatic actuators are very robust and can withstand higher pressures and temperatures than electric actuators.
Both pneumatic and electric actuators are efficient and powerful automation devices that can be used in various industries. However, they each have unique properties that make them more popular in different applications. To choose the best one for your application, carefully consider the above factors. If you want to buy pneumatic or electric actuators, please contact us.
UG Controls is a professional custom valve actuator manufacturer. We use our engineering expertise and industry experience to continuously improve our products, striving to provide efficient solutions and competitive prices. UG is also a global supplier of highly engineered actuators and accessories serving the oil and gas, mining, chemical, pharmaceutical, water and power, food and beverage, and general industrial markets.