Compressed air isnt free. Youd think that would be obvious to maintenance and operations personnel in plants where some of the largest motors are harnessed to compressors, howling and yammering away 24/7, sucking up, in many cases, the largest percentage of an increasingly outrageous utility bill. Wasting upwards of 30% of that energy should probably be illegal, but its not, and apparently most folks are oblivious.
If water or oil are leaking, you know it, says Len Bishop, manager, Draw Professional Services (www.drawproservices.com). If gas is leaking, you smell it. You can see steam. But compressed air? Its not a safety issue until someone complains that its too loud. So unless its knocking your hat off, you ignore it.
Statistics from the Compressed Air Challenge (CAC) and DOE are confirmed by the compressed air system experts: The average facility has 30% to 35% leakage if it hasnt taken any recent action. And a survey by the Office of Industrial Technologies says 57% of facilities have taken no action during the past two years.
Air is a clear fluid that doesnt make a mess, says David Booth, system specialist, Sullair (www.sullair.com). It can leak forever and not directly affect anything but cost. So, unfortunately, leaks are a big component that no one is willing to fix permanently.
Even a 1/16 inch diameter leak can cost big bucks (Figure 1). But you neednt get out a caliper. If you can hear it without an ultrasonic leak detector, its at least 8 cfm to 10 cfm at $300 per year per cfm, says Bishop. It may not be a safety issue, but its costing you money.
The excess cost goes beyond wasted energy. Leaks lead to other plant problems:
- Fluctuating system pressure: Inconsistent or faulty performance of air tools and other air-operated and powered equipment.
- Excess compressor capacity: higher than necessary equipment and maintenance costs. Not only are you wasting energy, youre likely to be mismatching the compressor, says John Bartos, vice president of engineering and new product development, Cooper Compression (www.coopercameron.com). You buy based on calculated demand, and leaks can really affect the actual performance.
- Excess load on supply equipment: Increased maintenance costs, decreased service life.
- Thwarting other system efficiency efforts: Its impossible to optimize system pressure and compressor control schemes with excessive leaks. In cases where the total leak load exceeds 10%, the artificial demand created by leaks must be addressed in order to obtain an accurate air demand profile for the plant, says Wayne Perry, technical director, Kaeser Compressors (www.kaeser.com). Only then can other recommendations and improvements take place.
- Wet air: While letting air out, leaks let moisture in. Valves on drain legs are left cracked open because too much water is coming into the equipment, says Scott Stroup, president, Airometrix Manufacturing (www.airometrix.com). But unless the air dryer is malfunctioning, the air is leaving it at a -40 degree dewpoint. Wheres the water coming from? It comes in at the air leaks.
Its counterintuitive, but Ficks Law explains why water migrates from high-humidity outside air into dry compressed air even though air is coming out the leak. Its hard and for some people, impossible to believe, but its true, Stroup says. Is your water problem bigger when the humidity is high or its raining? Thats why.
So with all these potential benefits, why is it that, as Jan Zuercher, director, air systems, Quincy Compressor (www.quincycompressor.com), says, Most people do very little leak management a majority do it infrequently or not at all.
Some plants are ignorant, more feel they cant devote time and effort to leak management, and plenty see it as pointless: fixing some leaks makes the others leak more, and youre back to zero (see sidebar, Exercise in futility?). But understanding where most leaks occur, efficient ways to detect them, and their effects on system pressure and performance can help you implement an energy-saving leak management program thats simple, efficient, rewarding and, dare we say, almost fun.
Before you start shopping for leak detection equipment or get bogged down seeking management support, its helpful to know where many of the largest leaks are likely to be found (Table 1). Drawing on his extensive experience, Stroup provides this ranking:
- Hoses and hose fittings: On hoses, the fitting-to-hose connections are most likely due to improper clamping or working loose. Next comes the hose itself, cut or gashed, Stroup says, then the quick-disconnects.
- Pressure regulators and filter/regulator/lubricators (FRLs): The stems on the filter bowls leak or are left open, O-rings leak at the bowl-to-housing connection, filter bowls are cracked, and on the regulators themselves, O-rings, gaskets and the piping connections between elements often leak.
- Plastic tubing: There are so many of them, the sheer number adds up, Stroup says. The leaks are mainly at push-to-connect fittings.Zuercher agrees that tubing connectors are a common cause of leaks, but says, Theyre typically too small to be worth repairing. Fix the largest leaks first to get the biggest bang for the buck.
- Header and distribution piping: Welded steel and soldered copper pipe are generally pretty tight, Stroup says. Threaded pipe is more likely to leak.
- Leaks within equipment: In some plants, these are a major concern. A small hole there can go undetected and cause a pressure drop that leads to an equipment malfunction, says Stroup. People end up replacing a cylinder or solenoid valve trying to fix an intermittent equipment problem thats actually caused by an undetected leak.
For example, a packaging machine wouldnt work properly when other equipment in the area was running. Mechanics replaced a solenoid valve with no effect. When we got next to it, we could hear a leak, Stroup says. We crawled under it and found where a chain had worn a hole in an air line. Fixing that fixed the problem with the machine.