Like fuel, water and electricity compressed air is a vital utility that 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 fill tires, run air tools, spray paint and keep basketballs from going flat.

Reciprocating compressors are the type you are 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 downward, 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 reciprocator constantly without giving it time to cool will result in overheating, which is a major cause of premature compressor failure.

To avoid overheating, the compressor should be sized 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 start. 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 less than three-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 and 400°F, accelerating oil deterioration and causing carbon to form on the valves and keep them from sealing. Most of the time this just 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. The synthetic base oils provide greater oxidation resistance, lower carbon forming tendencies and higher oil film strength than is possible with commonly used mineral oils. This extra protection will help protect the compressor when it’s being pushed to its 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 provided with 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 VG 100 or SAE 30/40 oil. When these are listed, AMSOIL ISO 100, SAE 30/40 Synthetic Compressor Oil (PCK) is the recommended product. We make it easy by listing all the viscosities on the quart label.