Spring is the time of year when we start opening the windows and doors at the plant for some fresh air. As the temperature warms, it can start to take a toll on your air compressors. Luckily, the basics of air compressor maintenance are simple, but critical. Spring means warmer weather is coming, and in some cases, less forgiving operations for compressors. As always, follow your manufacturer specified maintenance. However, keep in mind that these recommendations are based on machine longevity, not energy efficiency. More frequent air compressor maintenance will increase performance and save operating dollars.
HEAT, The Enemy
Heat not only causes motors, bearings and oil to break down, heat literally makes the compressor do more work for the same volume of compressed air and if not maintained, can lead to all types of system issues. Air compressors are heat rejection machines as roughly 95% of the energy an air compressor uses is rejected to the surroundings as heat! Also consider that hotter summer air can hold more moisture, which damages our compressed air systems, making springtime air compressor maintenance critical.
Air Compressor Intercooler
Intercoolers cool the air between stages, increasing the compression efficiency of the machine. More cooling equals higher efficiency. Dirty intercoolers increase power consumption because hot air requires more energy to compress than cooler air. As temperatures in the compressor increase with weather, keeping this intercooler squeaky clean is very important for performance.
Air Compressor Aftercooler
Aftercoolers are, you guessed it, after the compression is complete. The aftercooler brings down the temperature of the now hot, recently compressed air. This cooling causes a significant portion of the moisture in the air to condense out, reducing the moisture load on the dryer. Aftercoolers should discharge air about 20 F above the ambient temperature. Lower temperature is better and means less water the dryer has to remove. Keeping the aftercooler clean becomes more important as the weather warms.
Air Compressor Oil Cooler
Oil coolers keep compressor oil below 190F (ideally 180-185 F). Above 190-195 F, the oil life begins to be significantly shortened (25% reduction in life) as the oil develops tanins. If the oil temperature increases more, the oil life is further degraded. Oil at 200F will have half the useful life it would have at 180F. Beyond just the cost of frequent oil changes, high oil temperatures lead to very damaging varnish in the oil passages that degrades performance and is costly to remove.
Conversely, cooler oil (below 180) will begin to carry water with it, causing less heat rejection, lower oil lubricity, early air end bearing failure, and premature failure of other components lubricated by the compressor oil. Keep the oil cooler clean and watch compressor oil temperatures on your daily rounds to catch low or high oil temperatures early.
“OK, that is a lot of info. What should we do for preventative air compressor maintenance?”
Regular testing of compressor oil as it ages will show oil breakdown before it becomes problematic. This predictive testing can be done very affordably on site with a TAN (Total Acid Number) test kit. It is also highly recommended to periodically send out oil for testing at a lab to look for indications of other serious problems that a TAN kit can’t test for. Contact us for TAN test kits or a free oil sample kit.
Compressor Inlet Air
As we said above, air that is already hot requires more energy for the same flow rate at the compressor outlet. Cold, clean, dry air is what your air compressor needs at the inlet. Sometimes this isn’t in the compressor room. Consult your owner’s manual for pipe size requirements for remotely locating the air inlet and filter. Of course, temperature isn’t everything. Make sure the air inlet is in a location well away from dirt, dust, contaminants and cooling towers. Locate the air inlet somewhere easily accessible for changing the inlet air filter.
3 Types of Dryers
Compressed Air Dryer
Most plants utilize compressed air dryers to ensure their plant air does not carry excessive moisture. How dry the air needs to be determines the type of dryer that is right for the application. Many facilities are attempting to achieve lower dew points than are necessary for their application to compensate for a poorly designed, neglected, or overly expanded system. Other facilities have a mix of dryer types using a common plant header. Not only does this lead to poor dew point control, it also leads to elevated operating costs as lower dew points take more energy to achieve.
Pro tip: Consider a smaller dedicated dryer for the most sensitive equipment and a large, more economical dryer for the entire system.
Water that makes it to the plant system will wreak havoc. Pneumatic tools and valves will have a shortened life due to corrosion and reduce oil lubricity. Inline filter regulators will be damaged by slugs of water. Plasma or laser heads are sensitive and also easily damaged by unwanted water. Of course, if air is in contact with product, this condensate can cause major contamination as it is a breeding ground for fungus and bacteria.
A refrigerated dryer works together with the aftercooler to remove moisture from compressed air. If the aftercooler is dirty, the refrigerated dryer may be unable to do its job. Much like a large chiller or air conditioner, it is important to have a professional maintain your refrigerated dryer. However, the most important and simplest thing to maintaining a dryer is also the cheapest and easiest. Clean the condenser coils! Just like at home, a dirty condenser coil reduces heat transfer and drastically reduces the capacity and efficiency of your dryer. As temperature and humidity rise in our plants this spring, do your refrigerated dryer a favor and clean it at least once a month. More if it gets dirty quickly.
Desiccant dryers work with the aftercooler as well. If the aftercooler temperature is too high, the desiccant cannot properly dehumidify the compressed air. Further, the excess moisture will cause the dryer to cycle before the desiccant is regenerated, leading to poor dew point control and moisture problems. While desiccant dryers do not get dirty condenser coils, the desiccant can become fouled. Regularly sample and test desiccant and the system dew point to ensure everything is working as it should.
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Compressed Air Condensate, The Other Bad Guy
Air holds less moisture as pressure increases. So, compressing humid air on a spring day causes a lot of water to come out of the air. This water is called ‘condensate’ because it condenses as the compressed air cools. Properly designed air systems have intercoolers, aftercoolers, and air dryers to remove this condensate so it doesn’t end up in your distribution system. In the winter, that condensate can freeze, damaging distribution piping. In the summer, that condensate sits in the system, causing corrosion, bacterial and fungal growth, and ends up in your product. That is why it is important to help your system get the condensate out and verify it is working properly during your spring air compressor preventative maintenance.
Condensate Traps or Solenoid Valves
If everything is working flawlessly at the compressor and dryer, there shouldn’t be condensate in the system. However, spikes in demand, dirty or worn equipment, or other issues can cause moisture to get in. Make sure these devices are completely removing water from the compressed air distribution system. Check for clogged traps that are backing up condensate, or stuck open traps that are leaking air. If replacing a solenoid valve on a timer, consider replacing it with a zero-loss trap. In addition to not being a deafening nuisance (I almost mess myself when these open!), a zero-loss trap will save a lot of money over its life by always opening when it needs to, and never when it doesn’t need to.
Compressed Air Drains and Drops
Periodically go to each air ‘drop’ off the header, any header drains and storage vessels and crack the drain valve open to ensure clean dry air is all that is coming out. The presence of moisture indicates a problem that should be addressed. Left untreated, moisture will cause leaks and leaks waste valuable compressed air and energy!
Compressed Air Pressure Loss
The rule of thumb for air compressor systems operating around 100 psig is this: Every 2 psi above or below 100 psig is 1% energy efficiency lost or gained. Know what your ideal plant pressure is and don’t assume. Many facilities are running at pressures higher than what is required by their equipment, resulting in unnecessary energy consumption.
Compressed Air Filters
So, if my equipment needs 100 psig compressed air, and the dirty inline filter causes 6 psig pressure loss, then changing the filter cartridge for a new one with only 2 psi pressure loss could save 2% of energy costs. The same could be said for the compressor inlet air filter.
Inlet Air Filter
If the inlet air pressure differential gauge is reading above 2-3 psig, change the inlet air filter. Don’t have an inlet differential pressure gauge? You should. It is highly recommended if you want to save energy. Minimum recommended inlet air filter interval is twice per year. Your environment may require more frequent changes.
Inline Air Filters
Inline filters and point of use filters have a tendency of reaching that “change filter indicator” point due to saturation and, if ignored long enough, the air pressure will eventually find a weak spot and punch a hole through the element rendering the pressure differential indicator useless. Rule of thumb is to change these elements annually or once the indicator reaches 6-8 PSI, yellow on most indicators. Even if the change filter indicator is green, the filter be inspected a minimum of twice times per year to ensure the filter element hasn’t been compromised.
Lets Do The Math
A 100 horsepower compressor operating continuously at a cost of $0.08/kWh has an annual energy cost of $63,232. 2% of that is $1,265 per year! That buys a lot of air filters. Just saying. How many hundreds of compressor horsepower lives at your plant? How often are all those filters changed? Any other pressure losses in the facility you can eliminate? We’d love to help!
Snap a picture and send it to us in live chat at www.rasmech.com. We can get you the filters, zero-leak traps, oil or whatever else you need for your spring checklist.
Have questions or want to really get serious with your energy savings? Unsure about your air compressor maintenance plan? Call us at 1-800-237-3141, email email@example.com, chat with a support agent, or contact us online. We would be happy to come by and help you out.