AME Unit 11 Q7

A volume booster is a device used to amplify the air supply to a pneumatic actuator. It’s commonly fitted to a pneumatic process valve for several reasons:

1. Increased Actuator Speed:

• By providing a larger volume of air, the volume booster can accelerate the actuator’s response time, allowing for faster valve opening or closing.
• This is crucial in applications where rapid valve actuation is required, such as emergency shutdowns or fast-acting control loops.

2. Overcoming Back Pressure:

• In systems with high back pressure, the actuator may struggle to overcome the resistance and achieve full stroke.
• A volume booster can provide the additional air supply needed to counteract the back pressure and ensure complete valve travel.

3. Consistent Performance:

• By maintaining a stable and sufficient air supply, a volume booster helps to ensure consistent valve performance across a wide range of operating conditions.
• This is particularly important in applications where valve reliability and accuracy are critical.

4. Handling Large Actuators:

• For large-sized actuators that require significant air volume to operate, a volume booster is essential to provide the necessary power.
• This is common in valves used in high-pressure or large-diameter pipelines.

By addressing these factors, the volume booster enhances the overall performance and reliability of the pneumatic process valve.

A feedback positioner is a device that improves the accuracy and response of a pneumatic process valve. Here are the primary reasons for fitting one:

1. Improved Accuracy:

• Eliminates hysteresis: Positioners compensate for the valve’s inherent hysteresis, ensuring that the valve stem position accurately reflects the control signal.
• Overcomes friction: Friction in the valve stem can prevent accurate positioning. Positioners provide the necessary force to overcome this friction.

2. Faster Response Time:

• Reduces stiction: Positioners help to overcome the static friction (stiction) that occurs when the valve is initially opened or closed.
• Amplifies control signal: By amplifying the control signal, positioners enable faster valve movement.

3. Consistent Performance:

• Compensates for changes in supply pressure: Positioners maintain consistent valve performance even if the supply air pressure fluctuates.
• Handles back pressure: Positioners can overcome back pressure on the valve, ensuring full valve travel.

4. Remote Monitoring:

• Many positioners include a feedback signal that allows for remote monitoring of the valve position. This is essential for troubleshooting and process optimization.

5. Increased Control Range:

• By amplifying the control signal, positioners can extend the control range of the valve, allowing for finer adjustments.

In essence, a feedback positioner enhances the performance of a pneumatic process valve by improving accuracy, speed, and reliability.

For a fuel supply system where the valve must not move on loss of power to the control system, a spring-return pneumatic actuator is the most suitable choice.

Reasons for Choosing a Spring-Return Pneumatic Actuator:

• Fail-safe position: In the event of a power failure, the compressed air supply to the actuator is lost. The spring within the actuator will then return the valve to its default (closed) position, preventing fuel leakage.
• Reliability: Pneumatic systems are generally more reliable than electric or hydraulic systems in harsh environments.
• Speed of operation: Pneumatic actuators can provide rapid valve actuation when required.
• Safety: The fail-safe nature of the spring-return actuator contributes to overall system safety.

Additional considerations:

• Actuator size: The actuator must be sized correctly to provide sufficient force to operate the valve.
• Spring force: The spring force should be adequate to overcome any potential back pressure on the valve.
• Safety devices: Additional safety devices, such as solenoid valves and interlocks, can be incorporated to enhance system reliability.

By selecting a spring-return pneumatic actuator, the fuel supply system is designed to prioritize safety and prevent uncontrolled fuel flow in case of power loss.

A pneumatic actuator with a double-acting design is typically suitable for process valves in a lubrication oil cooling system.

Reasons for Choosing a Double-Acting Pneumatic Actuator:

• Bidirectional control: This type of actuator can open and close the valve in both directions, allowing for precise control of oil flow through the cooler.   1. Single-Acting vs. Double-Acting Valve Actuators – Gemini Valve www.geminivalve.com
• Speed control: The speed of valve operation can be adjusted by controlling the air supply to the actuator.
• Reliability: Pneumatic systems are generally robust and reliable in industrial environments.   1. Industrial Applications of Pneumatic Systems | JHFOSTER jhfoster.com
• Safety: Pneumatic systems are inherently safer than hydraulic or electrical systems in many applications.   1. Understanding the Key Differences Between Hydraulics and Pneumatics – Titan Fittings www.titanfittings.com
• Flexibility: Double-acting actuators can be used with various valve types, including ball, globe, and butterfly valves.

Additional considerations:

• Actuator size: The actuator should be sized appropriately to match the valve size and the required flow rate.
• Positioner: For precise control, a feedback positioner can be added to the actuator.
• Fail-safe mechanism: Depending on the specific application, a fail-safe mechanism (e.g., spring return) might be necessary.

By selecting a double-acting pneumatic actuator, the lubrication oil cooling system can effectively regulate oil temperature through precise control of the bypass valve.