Sign up for the ControlAir newsletter.
Get news, updates, and offers direct to your inbox.
What Is a Pneumatic Volume Booster? How It Works, Applications & Selection
A pneumatic volume booster is a pilot-operated pressure control device that increases the volume of compressed air delivered to a pneumatic actuator or other downstream equipment. It uses a low-flow pneumatic control signal to regulate a much larger airflow from an independent air supply, improving actuator response time while maintaining the required output pressure.
Volume boosters are commonly used with control valves, diaphragm actuators, piston actuators and industrial automation systems where a pressure regulator, I/P transducer or valve positioner cannot supply enough airflow to achieve the desired operating speed.
How Does a Pneumatic Volume Booster Work?
A pneumatic volume booster operates using a pilot pressure signal rather than relying solely on a manually adjusted spring, as found in many conventional pressure regulators.
The pilot signal acts on a diaphragm assembly that controls the booster’s internal supply and exhaust valves. This allows the booster to deliver or exhaust a larger volume of compressed air while responding to changes in the control signal.
A typical pneumatic volume booster circuit includes four main connections or pressure paths:
- Supply Pressure: Compressed air supplied to the booster from an independent air source.
- Signal (Pilot) Pressure: The control pressure supplied by a regulator, I/P transducer, valve positioner or other pressure-modulating device.
- Output Pressure: The regulated downstream pressure delivered to the pneumatic actuator or equipment.
- Exhaust: The path that allows excess downstream air to escape when output pressure must decrease.
Step-by-Step Operation
- The pilot signal enters the booster. A pneumatic pressure signal acts on the booster’s control diaphragm.
- The booster senses the required output pressure. The internal mechanism compares the pilot signal with feedback from the downstream output pressure.
- The supply valve opens when additional air is required. Compressed air flows from the independent supply through the booster to the actuator.
- Output pressure rises toward the commanded pressure. As the forces approach balance, the supply valve closes or reduces flow.
- The exhaust valve opens when pressure must decrease. The booster releases downstream air, allowing the actuator pressure to fall in response to the pilot signal.
This process allows a relatively small pneumatic signal to control a much larger volume of compressed air.
The primary benefit of a volume booster is increased airflow capacity, not necessarily increased pressure. Many volume boosters maintain a 1:1 signal-to-output pressure ratio, meaning the output pressure follows the pilot pressure while the booster supplies significantly more airflow.
Why Is a Pneumatic Volume Booster Used?
The main purpose of a pneumatic volume booster is to increase the speed and responsiveness of pneumatic equipment by delivering greater airflow than the original control device can provide.
Large pneumatic actuators often require substantial volumes of compressed air to move between positions.
When airflow is limited, the actuator may respond slowly, even when the control signal pressure is correct.
Installing a properly sized volume booster allows the actuator to fill and exhaust more quickly, reducing the time required for valve movement.
Key Benefits of Pneumatic Volume Boosters
- Faster Actuator Response: Increased supply and exhaust airflow can reduce the time required for pneumatic actuators to change position.
- Higher Flow Capacity: A low-flow control signal can regulate a much larger volume of compressed air.
- Improved Valve Positioning Response: Faster actuator movement can improve response to changes in the control signal when the system is properly tuned.
- Stable Pressure Control: Adjustable bypass valves and appropriate deadband characteristics can help balance response speed with stability.
- Remote Pressure Control: A pilot signal can control a higher-flow pneumatic output at a remote location.
- Flexible System Integration: Volume boosters can be used with pneumatic regulators, valve positioners and I/P transducers.
Where Is a Volume Booster Installed in a Pneumatic System?
In a typical control valve application, the volume booster is installed between the valve positioner and the pneumatic actuator.
The positioner sends a pneumatic control signal to the booster’s signal port. The booster receives compressed air from a separate supply line and delivers increased airflow to the actuator.
A typical arrangement is:
Valve Positioner → Volume Booster → Pneumatic Actuator
The booster also requires a suitable compressed-air supply connection.
This arrangement allows the positioner to control actuator pressure without having to deliver the full airflow required to move the actuator quickly.
For large actuators, multiple boosters or separate supply and exhaust arrangements may be used depending on the actuator design and control requirements.
What Is the Difference Between a Volume Booster and a Pressure Regulator?
Both devices control pneumatic pressure, but they serve different purposes.
A pressure regulator reduces supply pressure and maintains a desired downstream pressure. In a conventional manually adjusted regulator, the output setpoint is typically established by an adjustment spring.
A volume booster uses an external pilot pressure signal to control a higher-flow pneumatic output. Its primary purpose is to increase the airflow available to downstream equipment while following the commanded pressure.
A volume booster is therefore sometimes described as a pilot-operated regulator.
In many applications, a pressure regulator or I/P transducer provides the pilot signal, while the volume booster supplies the larger airflow required by the actuator.
What Does a 1:1 Signal-to-Output Ratio Mean?
A 1:1 signal-to-output pressure ratio means that the booster’s output pressure is designed to follow its pilot signal pressure at approximately the same value, within the device’s operating specifications.
For example, when a 1:1 volume booster receives a 30 psig pilot signal, it regulates its output toward approximately 30 psig, assuming sufficient supply pressure and appropriate operating conditions.
The booster does not simply increase 30 psig to a higher pressure. Instead, it makes a greater volume of compressed air available at the commanded pressure.
Some volume boosters are available with other signal-to-output ratios.
For example, ControlAir’s Type 600 Precision Volume Booster offers standard 1:1 operation along with additional amplified and reducing pressure-ratio configurations.
The appropriate ratio depends on the application’s required output pressure and control signal.
What Is the Purpose of a Bypass Valve in a Volume Booster?
An adjustable bypass valve allows a small amount of air to pass between the pilot signal and output circuit without requiring the main booster valve to open for every minor pressure adjustment.
This feature helps control the dynamic response of the pneumatic actuator.
A volume booster with excessive response can cause an actuator to oscillate or hunt around the desired position.
The bypass valve allows technicians to tune the response to achieve an appropriate balance between actuator speed and stable valve control.
The ideal bypass setting depends on the actuator volume, positioner characteristics, pneumatic tubing and application requirements.
Common Applications for Pneumatic Volume Boosters
Control Valve Actuation
Volume boosters are commonly installed between valve positioners and pneumatic actuators to increase airflow and improve valve stroking speed.
They are particularly useful for large control valves that require greater air volume than a positioner can deliver directly.
Large Diaphragm and Piston Actuators
Large actuators require substantial volumes of compressed air to move through their operating range.
A volume booster can reduce filling and exhausting time, improving actuator responsiveness.
Process Automation
Industrial process control systems often require valves to respond promptly to changing operating conditions.
Properly sized and tuned volume boosters can improve pneumatic response while maintaining stable pressure control.
Remote Pressure Control
Volume boosters can be used when a pneumatic control signal must regulate a higher-flow air supply at a remote location.
This can be beneficial where the pilot signal source has limited flow capacity.
I/P Transducer Applications
An I/P transducer converts an electrical current signal into a proportional pneumatic pressure signal.
When the I/P transducer does not provide enough airflow for the connected actuator or pneumatic device, a volume booster can increase the available output flow while following the transducer’s pressure signal.
Industrial Processing Environments
Pneumatic volume boosters are used in industries such as oil and gas, chemical processing, power generation and industrial manufacturing.
Applications vary according to actuator requirements, environmental conditions, material compatibility and system design.
How Do You Select the Right Pneumatic Volume Booster?
Selecting the correct pneumatic volume booster requires more than matching the port size or pressure range.
Engineers should evaluate the airflow requirements, actuator characteristics and desired control response before choosing a model.
Important selection considerations include:
- Actuator Size and Volume: Larger actuator chambers generally require greater airflow to achieve fast movement.
- Required Stroking Speed: Determine how quickly the actuator must open, close or change position.
- Forward Flow Capacity: Verify that the booster can deliver sufficient airflow to the actuator.
- Exhaust Capacity: Confirm that the booster can release downstream air quickly enough when pressure must decrease.
- Signal-to-Output Ratio: Select the pressure ratio required by the control system.
- Supply Pressure: Ensure adequate supply pressure is available for the desired output.
- Bypass and Stability Requirements: Consider whether adjustable bypass capability is needed to tune actuator response.
- Operating Environment: Evaluate temperature limits, housing materials, corrosion resistance and applicable certifications.
Why Does Volume Booster Sizing Matter?
An undersized volume booster may not provide enough airflow to achieve the required actuator speed.
An oversized or improperly tuned booster can produce excessively aggressive actuator response, potentially contributing to instability or oscillation.
Proper sizing helps achieve the required balance between speed, stability and pressure-control performance.
ControlAir Pneumatic Volume Booster Options
ControlAir offers pneumatic volume boosters designed for different flow requirements, pressure-control applications and operating environments.
Type 600 Precision Volume Booster
The Type 600 is a pilot-operated ratio relay designed to convert a low-flow pneumatic control signal into a higher-flow output.
It offers multiple signal-to-output pressure ratios and is suitable for flow boosting, pressure amplification and remote pressure control applications.
Type 625 Volume Booster
The Type 625 is a compact 1:1 signal-to-output volume booster designed to improve the response of diaphragm and piston valve actuators.
It features an adjustable bypass valve and fixed deadband to help maintain stable control while providing increased airflow.
Type 6000 and Type 6100 High Flow Capacity Volume Boosters
The Type 6000 and Type 6100 models provide additional options for applications requiring high pneumatic flow capacity.
The appropriate model depends on the required flow performance, actuator size, signal characteristics and installation requirements.
Stainless Steel Volume Boosters
ControlAir also offers stainless steel high-flow volume boosters, including the Type 6200 and Type 6600, for applications where environmental conditions or material requirements make stainless steel construction desirable.
Visit our Stainless Steel Volume Booster Page
Frequently Asked Questions About Pneumatic Volume Boosters
What is the main purpose of a pneumatic volume booster?
The main purpose of a pneumatic volume booster is to increase the airflow available to an actuator or other pneumatic device while maintaining the output pressure commanded by a pilot signal. This can improve actuator speed and system responsiveness.
Does a volume booster increase air pressure?
Not necessarily. Most standard 1:1 volume boosters increase airflow capacity rather than pressure. Some ratio relay volume boosters are available with amplified signal-to-output pressure ratios.
What is the difference between a volume booster and a valve positioner?
A valve positioner controls actuator pressure to achieve a desired valve position based on a command signal and valve-position feedback. A volume booster increases the airflow available to the actuator while responding to the pneumatic pressure signal.
The two devices are often used together.
When should a volume booster be installed?
A volume booster may be appropriate when a pneumatic actuator responds too slowly because the positioner, regulator or I/P transducer cannot deliver sufficient airflow. Actuator volume, required stroking speed and system stability should be evaluated before installation.
Can a volume booster improve valve actuator response time?
Yes. By increasing the available supply and exhaust airflow, a properly sized volume booster can reduce actuator filling and exhausting time, improving response to pressure commands.
What does a bypass valve do on a volume booster?
An adjustable bypass valve allows small pressure adjustments without opening the main booster valve. It helps technicians tune actuator response and reduce the risk of hunting or oscillation.
How do I size a pneumatic volume booster?
Sizing typically involves evaluating actuator volume, required stroke time, available supply pressure, forward and exhaust flow capacity, pressure ratio and system stability requirements.
A manufacturer sizing guide and performance curves can help identify an appropriate model.
Choosing the Right Volume Booster for Your Application
Pneumatic volume boosters play an important role in industrial pressure control systems by increasing available airflow and improving actuator responsiveness.
Whether the application involves a large control valve, pneumatic cylinder, I/P transducer or remote pressure-control system, selecting the correct booster can help improve response time and maintain stable operation.
ControlAir offers a range of pneumatic volume boosters, including precision, high-flow and stainless steel configurations.
Explore ControlAir’s Pneumatic Volume Boosters, review our Volume Booster Sizing Guide or contact our technical team for help selecting the appropriate model for your application.