What is a Flow Controller and What Does it Do?

By: Wayne Perry

A flow controller is essentially a pressure regulator that reacts very quickly to changes in downstream demand, releasing volumes of stored compressed air with precision to maintain very stable system pressure. Given adequate storage upstream, they can maintain system pressures within +/- 1 psig of target pressure even with large swings in demand. Too often, system pressure is set higher than needed to allow for fluctuation. With the precision flow controls, the target pressure setting can be reduced to the minimum required for the end uses.

Flow controllers present several significant energy savings and operating benefits, especially in older existing plants that don’t have the capital budgets available for major compressed air system re-designs. In many of these cases, system capacity is no longer well-matched to production demands.

By lowering the system pressure to its minimum, artificial demand is reduced. Further, the volume of air the compressors must produce is also reduced, so that leaks and other unregulated uses will consume less air. This is especially advantageous for installations with older piping where it may not be feasible to repair or upgrade the air distribution system. Given that the average compressed air system will leak about one third of the total air volume and unregulated uses can account for another one third, or more of total volume, this reduction in pressure can affect more than half of the total air supply. For example, if the downstream pressure can be dropped from 100 psig to 80 psig, and half of the demand is unregulated, the volume required to support the system will drop by about 10%. In a system using 2500 cfm, the drop in artificial demand (250 cfm) is equal to a 50 hp compressor. This is a conservative number since it is common that more than half of the system demand is unregulated.

In addition to reducing artificial demand, a flow controller can be used to support large intermittent demand events (like bag house purges) that might otherwise draw down the system pressure and even cause an additional compressor to start in order to rebuild the pressure.

The chart below shows a compressed air system before and after installing a flow controller.

Figure 1a

In this case, the plant was having problems with pressure swings and their supply was not quite able to meet demand. Their assumption was that a new air compressor was needed. Instead, a flow controller was installed and they were able to achieve a dramatic reduction in system pressure: from 82 psig to 69 psig, resulting in 6-1/2% power cost savings. This demand-side pressure reduction also reduced air loss due to leaks and unregulated usage by more than 13%—without fixing a leak. Adding the 6-1/2% savings from reducing the power, the 13% from the leaks, and an additional 3 – 4% for increased tool efficiency brings the total savings closer to 24%.

Another positive effect of using a flow controller to stabilize system pressure is an increase in productivity. With more stable system pressure, pneumatic devices operate more consistently, efficiently, and predictably. Nut runners, for example, will produce the same torque operation after operation with a stable pressure. Production machines will not alarm or stop due to fluctuations in system pressure. Product quality will improve. In some applications, stabilizing the air pressure has major production benefits that outweigh even large energy savings.

New installations, with today’s advanced electronic system controls, can achieve these benefits of pressure control without the use of flow controls. In many older systems, however, the flow controller offers stable system pressure without the need for advanced communications protocols—a huge benefit for systems that do not have the ability to easily connect with modern master system controllers.

This blog entry is an excerpt from our white paper, “The Proper Application of Pressure/Flow Controls”. To learn more, download the full version of the white paper here.