Control Valve Accessories - Principle, Purpose, Advantages

Control Valve Accessories - Principle, Purpose, Advantages

Control valves are essential for regulating fluid flow in a variety of industrial processes, providing precision and efficiency.

You can find more information on our website for additional resources and details.

According to the International Society of Automation, a control valve is defined as a power-operated device used to control the fluid flow rate in process control systems, making it a vital component in ensuring optimal system performance.

Control Valve Accessories

The control valve can be equipped with various accessories to enhance functionality. The most commonly used accessories are:

1. Pneumatic Positioners

2. I/P Transducers

3. Volume Boosters

4. Position Transmitters

5. Limit Switches

6. Solenoid Valves

7. Air Lock Relays

8. Handwheel

By equipping a control valve with these accessories, it becomes more reliable and efficient for process control. For example, pneumatic accessories ensure smooth operations and provide better response rates, which is crucial in industries like oil and gas, power generation, and manufacturing.

Purpose of Control Valve Accessories

The accessories added to control valves serve five primary purposes:

• Improve process control precision

• Enhance safety for processes and personnel

• Boost valve performance and response speed

• Monitor and verify valve responsiveness

• Diagnose and prevent potential valve issues

Modern control valve accessories, such as positioners and I/P transducers, can now interface with digital control systems, providing real-time feedback and diagnostics, which is essential in smart factories and automated process control systems.

Advantages of Valve Positioners

1. Minimizes the impact of friction, hysteresis, and dead band on the valve stem

2. Allows signal range adjustment

3. Enables control valve signal reversal (direct or reverse acting)

4. Increases actuator response speed

5. Allows changes to valve flow characteristics

6. Supports split range operations

Valve positioners are critical in reducing wear and tear on the control valve, ensuring that process control systems maintain their accuracy and efficiency even in demanding environments. These advantages have been further amplified by advancements in smart control technology, where positioners now play a key role in predictive maintenance and system optimization.

I/P Transducer

An I/P transducer, or current-to-pressure transducer, converts a 4-20 mA current signal into a 3-15 psi pressure output. These are particularly useful when high-precision positioning from a positioner isn’t required.

In applications where a direct electro-pneumatic system is sufficient, I/P transducers offer an economical and efficient solution for controlling actuators. The use of such transducers is becoming increasingly common in industries where control accuracy and cost-effectiveness are paramount.

Read: I/P Converter Principle

Volume Boosters

When control valve actuators have a large volume, their response speed may decrease. Volume boosters are added to increase the pneumatic thrust output, thus improving response time.

Single-acting actuators typically use one volume booster, while double-acting actuators require two or more. The inclusion of volume boosters is a key factor in maintaining fast and accurate valve operations in high-pressure or high-flow applications.

Read: Volume Booster Principle

Position Transmitter

A position transmitter provides real-time feedback on the valve’s position to the control system. This is essential for process monitoring and troubleshooting.

Position transmitters are commonly used in automated systems to ensure precise feedback on valve positioning, enabling operators to adjust or verify valve performance remotely from control rooms.

Read: Positioner Principle

Solenoid Valve

In some applications, solenoid valves are used to trap air inside the actuator, locking the valve in place. Alternatively, they can vent air to return the valve to a fail-safe position.

Solenoid valves play a crucial role in emergency shutdown systems, providing an additional layer of safety by ensuring valves return to a predefined position in the event of air supply failure or other process upsets.

Read: 2 Way Solenoid Valve

Limit Switches

Limit switches provide discrete signals to the control system when the valve reaches specific open or close positions. They are useful for process monitoring and system diagnostics.

Limit switches are typically installed in critical processes where valve position verification is necessary for safety and operational efficiency.

Read: Limit Switch Applications

Trip Systems – Air Lock Relay

Air lock relays are used in control systems to lock the valve in its last position in case of air supply failure. These systems are essential in applications where a specific actuator action is required upon air supply loss.

For double-acting actuators, air volume tanks can provide reserve air, ensuring that valves remain operational even during temporary air supply disruptions. Once the air pressure is restored, the system returns to normal operation automatically.

Read: Air Lock Relay Principle

Handwheel

Handwheels allow manual operation of the control valve when automated systems are unavailable or when manual intervention is required for maintenance.

In situations where precise manual control is necessary, handwheels provide a reliable alternative to automated valve operation, ensuring continued functionality during power or control system failures.

For more details, visit Xingyu to explore our range of control valve accessories.