Should I lower system pressure?

The following is a letter received from a concerned individual. Queries such as these are commonly a result of someone attending a Compressed Air Challenge seminar and learning about efficiency measures.

Question: We have a new maintenance supervisor that has turned down our shop air pressure to 86 PSI, supposedly saving operating cost. My opinion is it should be set between 90 and 100 PSI to accommodate surges. Is there really a significant savings by turning the supply down to 86 PSI?

Concerned Electrical Controls/Programmer

Answer:

Dear Concerned,

Yes indeed, lowering discharge pressure reduces the compressor motor power by about 1 percent for every two psi of lower pressure. Also, the lower pressure makes any unregulated uses in the "shop" re-duce consumption (cfm) by almost one percent for every one psi of pressure reduction. You will achieve extra savings if your compressor control systems can turn down compressor power in response to reduced flow or unload and possibly shut off unnecessary compressors.

The best pressure at which to set your system is the level your production can operate efficiently and effectively without waste; there is no right pressure, it depends on your machines. That being said, often you may have 90 to 100psig at the compressor, but at the production machine, where the actual work is being done. you could have only 65 to 70 psig. In some cases, it may be even lower due to pressure drops in undersized piping, filters, regulators, lubricators and tubing and connectors. The goal is to lower compressor discharge pressure, without affecting the end users. The method is to address these pressure differentials and get the pressure to the machines with minimal loss; then the compressor discharge pressure may be reduced even more. This is typically a job for a controls programmer like you.

Having artificially high plant pressure can help you deal with surges in compressed air demand that might occasionally cause low pressure and affect production. The higher pressure acts to store reserve air in the various volumes made up of receivers, pipes and such in your system. However, the higher pressure costs more to produce and makes unregulated end uses consume more air, which is an expensive trade off. Another strategy might be to use a pressure/flow controller and large storage receiver capacity in the compressor room. This will supply stored air for surges, but maintain lower plant pressures to reduce artificial demand caused by elevated pressures. Your compressed air service provider can assist with implementing this.

If you want to learn more about optimizing your system download the free resource "Improving Com-pressed Air Performance: A Sourcebook for Industry" written by the Compressed Air Challenge and the Department of Energy. Also check out our Compressed Air Best Practices Manual.

You may be interested in learning more in our upcoming web based compressed air Fundamentals seminar or the many in-person seminars across the country. For more information go to www.compressedairchallenge.org/calendar.