Sometimes, Proportion-Air’s standalone electronic pressure regulators do not flow enough for a customer’s process. In this situation, we pair our QB2X (most common) with a Proportion-Air air volume booster for increased flow capacity.

The Proportion-Air QB2 Air Volume Booster is not a specific product. It is a concept and a technology that we use to increase the versatility of our product line and meet the needs of the customer.

Below are some examples of our electronic regulators being used as pilots to a variety of dome-loaded (air volume booster) pressure regulators. This is a tried and tested technology that we recommend to many customers. However, there are many nuances involved and we would love to help specify the combination that works best for your application.

A QB2X series electronic pressure controller used in conjunction with any of Proportion-Air’s air volume boosters will provide an increase (boost) in both forward and reverse flow. But what’s the purpose and how does an Air Volume Booster work? Imagine this scenario…

The Application Situation

Mark the Engineer has an application that requires tight pressure control from 0 to 90 PSI at an accuracy of ±0.5%. He will be controlling this pressure range in a static volume of 2500 cubic inches. Our QB1X model can control this pressure range at his desired accuracy, but with a max flow of 1.2 SCFM (ideal conditions), it would take the QB1X more than 5 minutes to pressurize Mark’s volume to 90 PSI.

Problem #1: Mark needs to pressurize this volume to 90 PSI in under 2 seconds!

This is where we implement a Proportion-Air air volume booster to increase the amount of flow into the process. By using our QBX to control the pressure on the dome side of the diaphragm in an air volume booster, we are able to control the process pressure through the volume booster as the forces on either side of the diaphragm naturally equal out. In other words, 90 psi on top of the diaphragm will naturally provide approximately 90 PSI on the bottom of the diaphragm, providing pressure control with higher flow.

Problem #2: Mark needs pressure accuracy of ±0.5% (in this case: ±0.45 PSI)An air volume booster is a mechanical pressure regulator that we control electronically. But if we are controlling pressure on the dome, we cannot measure the pressure in the process. This means the pressure accuracy in the process is affected by the mechanical hysteresis and inaccuracies of our volume booster. We call this single-loop control and (depending on the air volume booster) accuracy can range from 1% to >5%. Sometimes this accuracy is okay and can even be preferred in some applications. But for Mark, this is a problem.

The Solution: Proportion-Air Dual-Loop Pressure ControlAfter we size and select the optimal air volume booster for Mark’s application, we add a 2nd loop so we can achieve the accuracy that Mark needs. In this case, our 2nd loop is a Proportion-Air DSB pressure transducer that we install on the output of the air volume booster. This transducer measures process pressure and constantly provides direct feedback to the QBX (now a QB2X). Our electronic controller now puts whatever pressure is required on the dome of the air volume booster to achieve the commanded pressure in the process. The accuracy (±0.5%) of the DSB transducer now drives the accuracy of the dual-loop volume air booster assembly.

Example Assemblies

volume air booster

Low Pressure


Control pressure as low as 0-2 Inches of Water Column with this High Resolution & High Flow, 1″ NPT pressure control assembly.

volume air booster

Standard Pressure


Control pressures from 0 to 175 PSI and achieve flow rates up to 2,000 SCFM while maintaining an accuracy of ±0.5% of full scale calibration.

volume air booster

High Pressure


Control pressure up to 5,000 PSI with this 45:1 ratio regulator assembly, while achieving accuracy of ±0.5% full scale calibration.

volume air booster



Control vacuum and achieve flow rates up to 100 SCFM with an accuracy of ±0.5% full scale with this high flow vacuum control assembly.

volume air booster

Hazardous Media


Control hazardous media like methane and natural gas at pressures from 0 to 150 PSI with this FM Approved ISQBX (single loop) and unpainted air volume booster.

volume air booster

Process Control


Control industrial processes and medias with these process air volume boosters with sizes from 1/2″ to 4″, and 6″ and 8″ flange options with very high CV ratings.