by Dan Leiss

Flipping through an air compressor owner's manual, many owners don't take the time to consider the simple things that can help them get the best return on their equipment investment.

Rental centers typically do a run-through of each compressor's maintenance checks to ensure the unit isn't returned nonfunctional, which would result in a lost day's rental. These checks only take a few minutes, but they can add months-or even years-to the service life of a machine.

Daily Maintenance

Always begin with a clean compressor. Check the hoses for kinks, inspect the electrical wiring for cuts and fraying and examine the tubing and piping for damage. Ensure the connections in all of those areas are tight and tighten any loose nuts or bolts. Look over the controls, gauges, accessories and instruments, making certain there are no loose mountings or damage.

Begin each day's use by checking the pump oil level. Disconnect the power source and place the compressor on a flat surface. Remove the oil fill plug and check the level, then insert a screwdriver into the crankcase. Inspect the oil on the screwdriver for signs of contaminants, such as water and dirt, and change the oil if any contamination is found. Otherwise, change the oil annually. If a gas engine powers the compressor, use this time to check the engine oil level as well, which also should be changed annually.

Be sure to install the correct type of air filter for the day's work. Using the wrong type of filter, or failing to use one at all, could bring on operating problems.

Once starting the compressor, be aware of any unusual noises or vibrations, which would indicate a potential problem. Knocking or vibrating could indicate a worn connecting rod or piston pin, dirt on the piston or a loose flywheel or pulley. Chatter at the pressure switch or magnetic starter may indicate the switch needs to be adjusted or replaced. Any noise out of the ordinary typically indicates that something is wrong.

At the end of each day, if not more frequently, drain condensation from the air tanks. As always, begin by disconnecting the power source. If the unit is portable, move it into an inclined position with the drain at the lowest point. Slowly open the drain and bleed the air from the tank(s). When the pressure drops to 10 psi, the valves can be fully opened and the tank(s) drained. Keep in mind that the condensate may contain oil, so it should be collected and disposed of properly.

Compressors operating in high-humidity areas will need to be drained more frequently than those in dryer climates. Moist air can take a toll on a compressor's longevity if the situation isn't appropriately addressed. Humidity may cause moisture to form in the pump and produce sludge in the lubricant, which will cause premature wear on the parts. When moisture begins to cause problems, an operator will typically notice that the lubricant looks milky or that condensation forms on the outside of the pump as it cools. The effects of humidity can be diminished by frequently draining the air tank and avoiding unheated storage areas since excessive moisture can build when moving a unit between temperature extremes. Increasing ventilation or operating the compressor for longer intervals also may help prevent moisture from forming in the pump.

Not So Often

The air filter should be inspected about once each week. Tap the dirt off and hold it up to a light. Are there bright spots of light coming through puncture holes in the filter? An exceptionally dirty filter should be replaced, as well, since it could wreak havoc on a compressor, costing much more in repair costs and time lost than an inexpensive filter replacement would cost. Keep in mind that compressors used in dusty environments will likely need filter replacements more often than a manual recommends. If there's ever any question about whether a filter needs to be changed, just replace it.

On a monthly basis, take time to check the safety relief valve. With the tanks emptied and the power source disconnected, pull and release the valve a few times. The plunger should move in and out. If it fails to do so after a few pulls-which should be enough to dislodge any dirt that might be causing the problem-the valve will leak and not actuate. A defective safety relief valve can often be detected when it "pops" or relieves pressure. Replace it with a new ASME-certified safety relief valve.

Air connections and compressor joints should be checked monthly for leaks. Begin by bringing the unit up to pressure, and then rub soapy water around all of the joints, fittings and hose connections. Air bubbles will form at the site of any leaks. Bleed off all of the air before tightening or replacing any parts.

Inspect the compressor's drive belt tension monthly. With the power supply disconnected and the control switches turned off, use a belt tension gauge attached between the motor and compressor sheaves to get a reading. Compare the reading to the compressor's service manual. If the belt's deflection is too great, loosen the bolts on the power source and slide the motor or engine away from the pump. Do the reverse if the deflection is too small. Recheck the tension after any adjustment is made.

End the monthly maintenance routine by checking all of the unit's bolts and tightening them as necessary.


Should a compressor experience a maintenance problem, the symptoms will likely provide clues regarding what went wrong. For instance, if the compressor is not producing enough air, it may be due to a leaky or dirty valve that needs to be tightened, cleaned or replaced. Other dirty or loose components also may trigger a lack of air, including the piston, piston rings, cylinder, inlet filter and discharge line filter or the culprit may be a lubricant viscosity that is too high.


A high lubricant viscosity might prevent the compressor from coming up to speed fast enough-or at all. Carbon buildup on the piston or a defective motor part, gasket or valve also could cause this, as could a worn connecting rod, piston pin, crank wrist pin bearing, crankshaft or crankshaft seal.

High oil consumption could be caused by a light duty cycle, damaged piston rings or excessive end gap, or a plugged oil crankcase vent. If the compressor becomes excessively hot, check the inlet filter and discharge line filter for dirt and ensure the lubricant level and type are correct. A number of other symptoms can cause either problem-oil consumption or heat-such as a low lubricant viscosity, an uneven surface or a worn cylinder, piston, connecting rod, piston pin, crank wrist pin bearing, crankshaft seal, crankshaft or cylinder.

Soapy water and a wire brush can be used to clean most parts. Avoid using a wire brush on softer parts, including anything made with brass or Teflon. Burnt on oil and carbon buildup may require Stoddard solvent. Worn parts, such as a scored cylinder or piston, will need to be replaced.

If the problem is caused by the lubricant, such as contamination or the wrong viscosity, change the oil. Inadequate lubricant levels, or using the wrong type, might cause excessive noise during operation.

Just a few minutes a day and some monthly preventive maintenance checks could make a big impact on a compressor's service life and the return on investment. In fact, following the manufacturer's guidance just might cause any potential compressor problems to virtually vanish into thin air.



Construction Business Owner, March 2010