The Ultimate Industrial Valve Selection Guide

The Ultimate Industrial Valve Selection Guide

Selecting Pneumatic and Electrical Actuators: Part 2

Modern process-control systems require an in-depth understanding of the specifications for each component in the control package. Since all components contribute to the automated valve's performance, it is vital to understand the functionality and constraints of each actuator part for overall success.

While valve actuators are fundamental to any valve automation package, additional elements significantly impact valve system communication and process/flow control needs, including:

• Pilot valves
• Limit switches
• Positioners
• Speed controls
• Transducers
• Various control accessories

An automated valve system should contain the following specifications:

• Valve size
• Valve type
• Model number
• Manufacturer
• Valve torque (in./lb.)
• Line pressure (Psi)
• Media temperature (°F)
• Media type (slurry, gas, etc.)

However, before proceeding to other specifications, you must first choose the type of valve actuator that best suits your requirements. The decision between a pneumatic or electric actuator will significantly influence the subsequent valve specifications.

Note: Consult the valve manufacturer for their specific Safety Factor recommendations.

Pneumatic vs. Electric Actuators

Both pneumatic and electric actuators exhibit efficacy across a variety of valve applications. The selection of one type over the other predominantly hinges on the specific requirements of your application.

The key factors to consider when comparing the two include:

• Power source
• Temperature range
• Environment/hazardous areas
• Duty cycle
• Stalling
• Speed control
• Modulating control
• Torque-to-weight ratio

For more detailed information on these considerations and additional variables, download our free eBook, "How to Select an Actuator."

Applications

Actuator torque and sizing are directly related to your valve's applications. If your valve manages clean liquids at moderate pressures and temperatures, the manufacturer’s specified operating torque typically aligns with your actuator size.

However, if your valve must function under different conditions (such as with unique liquids, extreme temperatures, or varying pressures), you may need to increase the torque for optimal operation.

In such instances, establishing a sizing safety factor based on the following guidelines is crucial:

Selecting an Electric Actuator

Electric actuators are geared motors equipped with various electrical components (including limit switches, heaters, and circuit boards) tailored for the exact automation requirements of a process-control system. Given that these actuators rely on electrical energy, they must be housed in enclosures designed for specific area classifications as per NEMA ratings.

A significant distinction between pneumatic and electric actuators is the power source driving their movements. In electric actuators, electricity powers the actuator to create movement.

Specifications Checklist

Here are crucial specifications to consider when selecting an electric actuator:

1. NEMA rating: Depending on your environment, select from NEMA 4, NEMA 7, or NEMA 4X for housing the actuator's electrical components.
2. Motor voltage: Ensure you have the correct voltage for driving your valve’s automation processes (e.g., 12, 24, 115, or 220 VAC or VDC).
3. Three-phase specific voltage
4. Compartment heater

Limit Switches

Electric actuator limit switches furnish the necessary number of electrical contacts for the open, closed, or intermediate valve positions. Most standard electric actuators feature two SPDT limit switches—one for the open position and another for the closed position—controlling rotary travel as required. You can also request additional contacts for open, closed, or intermediate positions.

Manual Override

A manual override serves as a safety and productivity measure, allowing valve operations in the event of an electrical failure or during startup and setup procedures. The handwheel should not rotate under normal operating conditions.

Torque Switches

Actuators with an output of in-lbs torque or higher may necessitate torque switches. These components are crucial for protecting your automated valve and motor, ensuring a secure closure for torque-seated valves.

Electronic Speed Control

Given that electric actuators employ geared motors with fixed speeds based on the gear layout, some manufacturers provide electronic speed controls that use a rotary output to enhance speeds (typically within 5-25 seconds for a 90° rotation). If you require a longer cycle time than what is specified, consider investing in an actuator with electronic speed control for improved cycle times.

Separate Controls

Numerous separate control options are available for electric actuators:

• Local/remote switch
• Three-position rotary switch (open/stop/close)
• Three-push buttons (open/stop/close)

Positioner

Electric actuators utilize positioners to adjust the valve in accordance with control signals. These positioners depend on input maDC signals and optional position transmitters.

To find more information, please visit Electro Pneumatic Valve.

Position Transmitter

A position transmitter provides ongoing feedback regarding the valve's position. These transmitters can be equipped with a slide wire (potentiometer) and come with either a two- or four-wire 4-20 maDC output. Two-wire outputs feature integral power supplies, while four-wire outputs require separate power supplies.

Indispensable Actuators from Indelac

Selecting the right electric pneumatic actuator can be a challenging process. At Indelac, we provide professional actuator consulting and services to a broad spectrum of clients. If you are unsure about the specifications you need, we are here to guide you through the selection process.

If you're interested in leveraging an electric actuator for your automated valve applications, contact us today.

For further information on Valve Accessories, please reach out. We are ready to provide you with expert answers.