Maintaining compressed air reliability requires attention

Known as the fourth utility, compressed air is used in many facets of manufacturing. Many plants use it in one capacity or another and, for the most part, these systems provide similar outputs. However, not all compressed air is identical. In several situations, specially engineered air powers a variety of machinery and tools used across several different industries, from automobile manufacturing to beverage processing.

Engineered air is a term that describes compressed air that has been tailored to meet at least three specific industry needs: 100% oil-free, particulate-free and completely reliable. It goes beyond identifying only a specified pressure. Engineered air provides the right type of air for the application. Engineered air reliability is a function of system redundancy, accessibility and maintenance, and technological advances in control and monitoring.

Redundancy

When an air compressor is vital to plant operations, a redundant system minimizes the possibility of system failure that can ruin production quotas. Examine your operation to see where air system redundancies might be useful. For example, the air compressor’s oil pump, the heart of the lubrication system, keeps the machine running smoothly. If the pump fails, the machine comes to a grinding halt. A redundant system would include two full-capacity, full-pressure pumps, one a shaft-driven main pump and the other a motor-driven auxiliary. During regular operations, the shaft-driven main pump operates, while the motor-driven auxiliary is on perpetual standby for emergency situations. Such a system provides full capacity backup. Without this redundant system, the entire compressor would need to be shut down in the event of an oil system malfunction.

Repairs

Although it requires additional time and attention from plant professionals, compressor cleaning and maintenance represent a sound investment. As with other plant assets, clean, well-maintained compressed air systems are less likely to break down. Simply put, less downtime allows for more production. In addition, consistent cleaning and maintenance minimize wear and tear, which saves money in replacement parts.

Many vendors design compressors with accessibility and maintenance in mind. The intercooler is a good example. For instance, using either U-shaped or straight intercooler tubes is standard industry practice. However, unlike the U-bend design, straight tubes are easier to clean. A plant engineer can simply remove the cooling water lines, unbolt the water box and rod the tubes in place. Rodding isn’t possible with U-bend tubes used in some compressors. In addition, intercooler tubes with a water-in-tube design are easier to clean and maintain than those with an air-in-tube design that requires wire brush or chemical bath cleaning. The longer it takes to clean the intercooler, the longer the engineered airflow is unavailable.

Journal bearings are another good example of important compressor parts that benefit from diligent maintenance and cleaning. Properly installed and maintained, these bearings can last for extended periods of time. Horizontally split bearings are easier to maintain, clean and replace because accessing them requires only removing the top half of the gear case. No other disassembly is required. Some compressors, on the other hand, have one-piece bearings that require complete compressor disassembly for cleaning and maintenance.

Interchangeable parts that save time and money is another factor that simplifies compressor maintenance. For example, multistage compressors use a bull gear and pinion system to power the impellers. The quality of the bull gears directly determines whether parts are interchangeable. The American Gear Manufacturers Association (AGMA) provides established gear quality ratings that range from 3 to 15.

If a compressor gear train features AGMA Quality Level 12 (or less) and either a bull gear or one of the pinions fail, all three will need to be replaced. On the other hand, AGMA Quality Level 13 gears, otherwise known as aircraft-quality gearing, are generally regarded as high-precision gears. They produce less noise and, under normal operating conditions, have a longer life. More importantly, though, gears and pinions manufactured to this standard are interchangeable. The plant maintenance technician only needs to swap out the damaged piece in question, which saves maintenance time and money.

Controls

Plants that use multiple compressors to feed a single-air system need to coordinate, monitor and control compressor operation. An initial investment in monitoring technology can ultimately pay for itself.

A PLC-based automatic sequencer can allow for as many as eight compressors to communicate with one another and operate as a team as it follows a programmed schedule. The sequencers monitor and match compressor supply to demand. For example, they can select which compressors to use, shutting down those not necessary to plant operations, even choosing backup units as needed. An automatic sequencer can ensure a stable system pressure, allowing your entire operation to run as efficiently as possible, saving both time and money.

PLC-based modular control systems can allow your plant operations engineers to monitor and perform diagnostic checks on your compressed air systems remotely, helping to predict and prevent systems malfunctions that could result in engineered-air downtime. These control systems should be easy to operate, resulting in less training time.

Engineered air is produced with increased reliability and efficiency with a specific plant application in mind. Recognizing that engineered air is not identical to compressed air is the first step to minimizing downtime and achieving better productivity. The systems that produce engineered air must, themselves, be engineered to operate as reliably as possible. Three points can help your plant engineers ensure the most reliable flow of engineered air possible:

• System redundancy, such as a dual-pump oil system, ensures engineered air is always available at full capacity.
• Accessibility and maintenance reduces the wear and tear on key machine parts, keeping the system running smoothly.
• Technological advances in control and monitoring provide the information needed to keep engineered airflow stable.

Addison Kelley is vice president of global customer support at FS-Elliott. Contact him at [email protected] and (724) 600-8900.