Compressed Air Challenge: Why Is Your Pressure So High?

By Ron Marshall, CET, CEM for the Compressed Air Challenge (CAC)

There was a day when most air compressors were rated at 100 psi: Rarely did general plant compressed air systems exceed this threshold. Over the years, however, plant pressures have climbed—and this has cost industrial customers a bundle.

A good exercise for anyone involved with compressed air systems in a plant is to question the pressures in those systems. Running your system at levels higher than what’s required costs about 1% for every 2 psi of extra pressure at levels around 100 psi. Moreover, unregulated air demands consume about 1% more flow for each 1 psi in added pressure. Excessive air pressure can cost about 10 to 15% more in wasted energy for every 10 psi increase. On a 100 HP air compressor running full time, this waste costs about $12,000 per year at 10 cents per kWh.

Why is your air pressure so high and what can be done about it? Here are some possible causes and solutions:

Pressure-critical end uses. There may be some air-using equipment that will malfunction if the pressure falls below a certain point. This forces compressor pressures higher. Many times these applications are attached to the system with poor connection practices, which can cause a 20 to 30 psi pressure differential. If these can be upgraded and improved, the pressure can lowered.

Perceived high-pressure applications. Equipment operators often think they need high compressed air pressure because of misinformation—or because “that’s the way it has always been done.” If a handful of questionable applications are forcing pressures up, it is time to question assumptions and verify actual requirements.

Piping loss. Compressor pressure may be jacked up because undersized main-plant piping is causing a restriction. Upgrading this piping size or reconfiguring it can remove restrictions and allow lower compressor pressure.

Dryer and filter differential. Many times, air dryers and filters in the compressor room are the culprits in causing restrictions. If the dryers are undersized or filters are clogged due to poor maintenance, the compressor pressure must rise to overcome this loss.

Transient demands. There may be occasional transient high-flow demands in the plant caused by a special compressed air process or machine. If this demand exceeds the capacity of the running compressors, the pressure may be pulled down to unacceptably low levels. As a way to compensate and prevent it from falling below what is minimally acceptable, the pressure is often jacked up to high levels. Applying local storage receivers as buffers can reduce transient demands

Factory default settings

Often, if a compressor is purchased with a high-pressure rating of say 125 psi, the factory default will be a set value near this capacity, sometimes for no particular reason other than “just because.” To save costs, plant pressures should only operate at levels required by legitimate end-users.

More information about the benefits of lowering compressed air pressure can be found at the CAC Website (compressedairchallenge.org) and in CAC’s Best Practices for Compressed Air Systems Manual. While you’re there, check out the online calendar for a schedule of upcoming training events. MT  

rcmarshall@hydro.mb.ca