Compressed Air Systems: PdM keeps compressed air systems running efficiently

Monitor to keep your compressed air predictable.

By Mike Bacidore, chief editor

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Compressed air systems are not inexpensive, and operating them can be costly, if routine monitoring isn’t done. A variety of predictive-maintenance technologies and strategies can be used to improve efficiency and avoid costly failures.

Clogged compressed air filters and leaking or failed condensate drains can cause contamination problems in downstream components and even contaminate the product itself, if it comes in contact, explains Ron Marshall, member of the project development committee, Compressed Air Challenge. “That nice oil sheen on the burger buns may look nice, but it is unhealthy to ingest,” he says. “Pressure differentials on main filters can be monitored during regular maintenance and changed before they cause problems. Clogged filters can back up compressed air flow and cause the compressors to run poorly, causing higher maintenance costs and a heavy energy penalty. Spend hundreds of dollars on a filter change or thousands of dollars on wasted energy.”

Because operating compressed air systems can be so costly, advanced data monitoring of equipment is one of the most effective strategies to improve compressed air system efficiency and avoid costly downtime, says Brian Blum, CTS optimization marketing/Department of Energy - Airmaster -, Atlas Copco Compressors. “Compressed air systems can consume up to 40% of the total energy a plant consumes on a yearly basis,” he explains. “Advanced data monitoring provides plant operators with the tools to recognize and react to performance changes in real-time, thus identifying issues before they become problems.”

Mike Bacidore is chief editor of Plant Services and has been an integral part of the Putman Media editorial team since 2007, when he was managing editor of Control Design magazine. Previously, he was editorial director at Hughes Communications and a portfolio manager of the human resources and labor law areas at Wolters Kluwer. Bacidore holds a BA from the University of Illinois and an MBA from Lake Forest Graduate School of Management. He is an award-winning columnist, earning a Gold Regional Award and a Silver National Award from the American Society of Business Publication Editors. He may be reached at 630-467-1300 ext. 444 or mbacidore@putman.net or check out his .

Compressed air systems can be the source of large hidden expenses within a facility, says Trent Phillips, condition monitoring manager, Ludeca. “Many facilities literarily waste money in the air and don't know it,” he offers. “A lot of critical job functions are dependent upon the on-demand availability of these systems. Most facilities assume that the air system will always be available until it fails and critical job functions can't be completed. A lot of facilities add additional compressed air systems, because their existing systems are unable to supply the required demand. However, no one ever asks why the additional capacity is required. Have additional processes been added or other things that require additional air capacity? Or is it simply due to a lack of maintenance?”

Proper maintenance of compressors would include monitoring of the bearings, explains Maureen Gribble, director, UE Systems. “Ultrasound is commonly used to monitor bearings and provides early indicators of bearing failures,” she says. “With bearings comes the need for lubrication, another area where ultrasound is an extremely effective tool. By utilizing ultrasound as a part of a reliability-centered lubrication program, you can determine exactly when your bearing requires lubrication, which will keep you from either over- or under-lubricating your bearings. Always important to remember is that nearly 70% of all bearing-related failures are due to lubrication.”

Air leaks can contribute up to 30% of air loss in a compressed air system, says Kirk Edwards, application engineer, Exair. “Most of these leaks are found at pipe, hose, or tube connections, and these connections should be dealt with carefully when concentrating on preventive and predictive maintenance,” he explains. “Choose quality fittings, pipe, hose, quick disconnects, and any other connection option. Make certain to apply thread sealant correctly and install the connections per their instructions. Any equipment that is no longer used or is used intermittently should have a compressed air supply with a valve so it may be turned off when not in use. Leaks can also be minimized by making sure to use as low an air supply pressure as possible, the lower the working pressure, the less air will escape a leak.”

Checking the compressors and pumps using vibration analysis will provide lots of benefit, says Michael D. Howard, MSc, CMRP, director, reliability solutions, Mobius Institute. “First, on commissioning or repair of a pump or compressor, it is crucial to ensure the asset has been repaired or manufactured to specification and within tolerances and that it is installed without introducing a potential failure mode,” he warns. “If the compressor or pump is as critical to the plant’s operation as most air systems are, an online vibration monitoring system may provide critical analytical data to allow you to plan and schedule maintenance on your terms, rather than the machine’s. At the very least, regular monitoring using route-based vibration analysis will enable the organization to ensure the asset is running at design efficiency between scheduled data collection intervals. If a pump or compressor is running, but running below the desired output due to a failure mode, then it has already failed the organization by RCM standards and is costing the organization money in lost efficiency, added monitoring and analysis costs, and ultimately repair when the failure mode presents enough to warrant repair, or, in the worst case, a functional failure occurs where the asset fails to perform its intended function at all.”

Using an adaptive system master controller helps spread out maintenance intervals, offers Waheed Chaudhry, engineering manager, Kaeser Compressors. “In addition to selecting the most energy-efficient combination of units to meet current demand, they also balance load hours among multiple units,” he explains. “This reduces wear and tear on the units and makes it possible to go longer between scheduled maintenance.”

Pipe thinning is a hidden defect, and it takes place before a leak develops, says T.J. Garten, subject matter expert — electrical, Allied Reliability. “Pipe thinning usually occurs in the area of elbows and where the pipe size changes step up or down; the air turbulence is greater in these areas,” he explains. “By monitoring and detecting pipe thinning, piping can be scheduled to be replaced before leaks occur. Predictive maintenance on the system is also very important as most compressors have filters, oil sight glasses, and pressure gauges. A simple PM to change the filters and record in a log book the output pressure, level of the oil, and visual condition of the oil can greatly increase the life and reliability of the compressor.”

The motor and compressor comprise the heart of the compressed air system, says John Bernet, vibration product specialist, Fluke. “If they were to fail, compressed air would not be available to supply any of the critical loads,” he explains. “The most common faults with rotating machines are imbalance, misalignment, looseness, and roller bearing wear. Using vibration meters to quickly screen these machines will give the operators and technicians the peace of mind they want that the machine will keep running, or they may need to take a closer look. If the vibration meter finds a problem, the operator or technician brings in the vibration tester and takes a more detailed measurement. The vibration tester will provide them with a diagnosis — machine fault, severity level, and recommended repair action. Using these quick and easy tools on the motor and air compressor builds confidence in maintenance schedules, budgeting, and productivity estimates.”

Process valves can number in the hundreds in a typical petrochemical plant or refinery, says Gus Velaquez, Latin American service manager, Spanish language corporate trainer, SDT International. “They must work flawlessly to keep the process up to standards,” he explains. “A high percentage of process valve actuators work pneumatically. Internal leaks in the diaphragm or compressed air system can render them unreliable; inspecting with ultrasound can detect these problems.”

Essentially, thermal imaging cameras used by PdM activities reveal equipment that is hotter or colder than a “normal status” reference temperature range, says Joe LiPetri, communications manager, Flir Commercial Systems. “Thermal cameras illustrate those temperature differences visually using varying on-screen color ranges or palettes,” he explains. “Thermal imaging for PdM on compressed air systems can be used on any component that heats up or fails to heat up, indicating less-than-optimal mechanical and/or electrical operation.”

Each PdM technology provides benefits to maintaining and operating a compressed air system, explains Daniel J. Hogan, vibration/oil analyst, Azima DLI. However, these technologies are best leveraged when used together in an integrated manner,” he says. “Credibility grows and accuracy improves when multiple technologies confirm a suspect mechanical problem. This can allow skeptical individuals to see the benefits of predictive technologies. Systems allow for the integration of multiple technologies and a common platform to collaborate making maintenance planning and repairs more effective.”

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  • One glaring omission from this article is the critical role that oil analysis can play in air compressor reliability and efficiency. By design, rotary screw air compressors ingest harmful contaminants (solids and vapors) and force them into the oil where they negatively impact compressor operation, and the service life of costly lubricants, bearings, shaft seals, coolers and other critical components. Routine oil analysis is an inexpensive tool that gives compressor users valuable and trendable information that can help them detect, correct, and avoid serious issues before they result in a major problem.

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