Compressors, Do You Have One?

Their prevalence in homes and businesses means nearly everyone needs a compressor

Mike Caruso | TECHNICAL PRODUCT MANAGER, DRIVETRAIN

Like fuel, water and electricity, compressed air is a vital utility we depend on to support our daily lives. We don’t receive a monthly compressed-air bill from a utility company, so it’s easy to forget how necessary and prevalent it is. Virtually every manufactured item requires compressed air for the creation of its raw materials or for its assembly, production, packaging or shipping. We use compressed air at home to inflate tires, run air tools and apply paint.

Reciprocating compressors are the type you’re most likely to encounter in your day-to-day activities. They are commonly found in the corner of a typical garage or the back room of a tire shop, and many of them require oil.

Reciprocating compressors use a piston and cylinder to compress air. A motor turns the crankshaft, causing the piston to move down, pulling air into the cylinder past a one-way intake valve. The piston then moves up, squeezing the air until enough pressure is created to push it through an exhaust valve into a tank. This type of compressor turns on and off as needed to cool between cycles. Running a standard reciprocating compressor constantly without giving it time to cool will result in overheating, which is a major cause of premature compressor failure.

To avoid overheating, size the compressor appropriately for the tools it’s intended to run. If the compressor is capable of putting out 2 cubic feet of air per minute (CFM), but the tool draws 4 CFM, the tool will only run
well in spurts and the compressor will never shut off while you’re using it. CFM is clearly identified in compressor and tool manuals or on the tools themselves, so there’s no math to do.

It’s just as damaging when compressors sit idle for weeks, giving rust and corrosion an opportunity to form. Since compressors are about as exciting as vacuum cleaners to most people, undersized and underused units are very common. The real excitement comes when you have to write a $500-$800 check to replace a four-year-old compressor that should have lasted more than a decade. Good oil can go a long way toward keeping these neglected compressors running for years.

Besides providing basic lubrication, reciprocating-compressor oils have to effectively deal with extreme heat and water – two potentially damaging byproducts of compressing air. Internal temperatures may range between 300°F-400°F (149°C-204°C), accelerating oil deterioration and causing carbon to form on the valves and keep them from sealing. Most of the time this gradually degrades compressor performance, but on rare occasions the carbon can become an ignition source for the oil-air vapor in the cylinder, presenting an explosion hazard. It has happened. Water, on the other hand, will destroy the compressor as rust and corrosion attack the machine while it sits quietly in the garage.

Like our motor oils, AMSOIL compressor oils are designed to handle severe environments. Their synthetic base oils provide greater oxidation resistance, lower carbon-forming tendencies and increased oil-film strength than conventional oils. This provides extra protection for compressors when they’re being pushed to their limit or if oil changes are neglected.

Water is dealt with in two ways. First, it easily separates from the oil, allowing it to be drained from the sump. This is a benefit for larger compressors found in industrial facilities, but is not practical for machines that hold a quart of oil. For these machines, the best way to protect against water is to change the oil at the manufacturer’s suggested drain interval and prevent rust and corrosion from starting regardless of the water situation. The high-quality anti-rust, anti-corrosion additives in AMSOIL compressor oils go a long way toward protecting the compressor through extended periods of idleness.

We are often asked which oil should be used in reciprocating compressors. By far the most common oil listed in reciprocating compressor manuals is non-detergent ISO 100 or SAE 30/40 oil. When these are listed, we
recommend AMSOIL ISO 100, SAE 30/40 Synthetic Compressor Oil (PCK). We make it easy by listing all the viscosities on the quart label.

Reproduced With The Permission Of AMSOIL INC. All Rights Reserved.

SLS Notes: While this article is primarily geared toward commercial applications (service garages, manufacturing facilities, contractors etc.), it will also apply to many homeowners who have compressors for the home mechanic / handyman. Whether professional or home use, a few simple tips will help you get the most life out of your compressor.

  • Check the oil level every day before starting the compressor.
  • Drain the air when you are through using the compressor for the day. This helps remove the water that can accumulate, rust the tank and lead to premature failure.
  • If you have a large commercial compressor, consider a blow-off valve similar to that used on truck air brake systems.
  • Change the compressor oil at the manufacturers recommended interval (usually 500 hours) or once a year, whichever comes first.
  • If the compressor is a commercial type unit that uses multiple quarts of oil, consider putting a valve on the drain line that will let you bleed condensation off the bottom of the compressor fluid. AMSOIL synthetic compressor fluids will separate from water that can build up in the compressor sump. (Mineral oils usually end up as emulsified oil/water mix.) Best time to drain, first thing in the morning or after sitting idle for a few hours.
  • Change the air filter at regular intervals. The better the air filter, the cleaner your air and the longer your compressor will last. You know it’s important to keep a good air filter on your car, the same holds for a compressor.
  • If you have a gasoline or diesel powered compressor, make sure you change the engine oil (and filter if there is one) regularly.
  • And finally, if you have an oil-less / oil-free compressor, keep in mind that everything mentioned above still applies, particularly using good air filters. The only exception, you don’t have to change the oil in the compressor.

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