Compressed Air System

Maintenance of compressed air systems pays off in equipment reliability

Don't leave your compressor's maintenance schedule up in the air.

By Dan Leiss, Jenny Products

In brief:

  • Timely maintenance on reciprocating compressors has a large payoff in terms of equipment reliability.
  • The daily routine maintenance for is simple enough to be incorporated into an autonomous maintenance program.
  • Some of the less frequent maintenance tasks require the compressor to be offline to give technicians suitable access.

Air compressors are the workhorses behind many operations. Assembly and maintenance professionals rely on this equipment every day to perform their daily tasks, so if a compressor breaks down, plant efficiency obviously comes to a halt, as well.

Considering compressed air’s value, keeping compressors well-maintained should be a high priority. Sure, these machines are designed to provide years of service, but to live up to expectations, they’re going to need a little attention.

Everyday maintenance

While there are many air compressor sizes and types, we’ll focus on reciprocating units, which are sometimes overshadowed by larger systems, but are equally important to many operations. Most of the daily maintenance tasks for reciprocating compressors are rather elementary, such as keeping the unit clean, inspecting the electrical wiring, checking the pump oil level, looking for air leaks and tightening loose components. However, a few more factors sometimes are missed.

For starters, be sure to install the correct air filter. Multiple types are available, and using the wrong filter, or failing to use one, could cause problems. For example, a standard filter traps dust particles based upon micron size, while a coalescing filter removes water and oil. For some applications, such as spraying paint, a dryer to remove moisture should be used with the coalescing filter. On the other hand, some tools function better with some moisture. When using an air wrench, for instance, an operator might want to add oil to the line with a lubricator.

Sure, these machines are designed to provide years of service, but to live up to expectations, they’re going to need a little attention.

Next, it’s important that air tanks be drained at the end of each day, if not more frequently. Disconnect the power source and slowly open the drain to bleed the air from the tanks. When the pressure drops to 10 psi, the valves can be opened fully and the tanks drained. Keep in mind that the condensate might contain oil, so collect and dispose of it properly.

Compressors operating in high-humidity areas need to be drained more frequently than those in drier climates. Moist air can take a toll on a compressor’s longevity if the situation isn’t appropriately addressed. Humidity can cause moisture to form in the pump and produce sludge in the lubricant, which will cause premature wear. When moisture begins to cause problems, an operator typically notices 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. Increasing ventilation or operating the compressor for longer intervals also might help prevent moisture from forming in the pump.

Not so often

While a number of small maintenance tasks should be done daily, several others, while still important, can be performed less frequently. For instance, the air filter should be cleaned about once each week and replaced if it’s damaged or exceptionally dirty. The pump oil should also be changed either yearly or whenever it’s contaminated.

To check for contamination, insert and remove a clean screwdriver into the crankcase. Then, inspect the oil on the screwdriver for dirt or other foreign objects. When changing oil, use the type the manufacturer specified, rather than whatever’s on hand. Otherwise, a lubricant with too high of a viscosity might prevent the compressor from coming up to speed fast enough, or at all. On the other hand, a low lubricant viscosity might cause the unit to run hot, which might lead to premature wear.

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 dirt that might be causing the problem, the valve will leak and not actuate. A defective safety relief valve often can be detected when it pops or relieves pressure. Replace it with a new ASME-certified safety relief valve.

Next, inspect the drive belt tension monthly. Use a belt tension gauge attached between the motor and compressor sheaves to get a reading. Then, compare the reading to the compressor’s service manual. If the belt deflects too much, loosen the bolts on the motor and slide it away from the pump. Do the reverse if deflection is too small.

Internal components, such as the piston or rod, rarely need maintenance. But in the event that these parts need service, a simple cleaning often will do the trick. 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 might require Stoddard solvent. However, worn parts, such as a scored cylinder or piston, will need to be replaced.

Occasionally, it’s a good idea to check the pilot valve cut-out pressure adjustment. Begin by cleaning dirt from the valve seat and adjust the valve according to manufacturer specifications. Typically, this involves turning the outermost screw on the pilot valve clockwise to increase the cut-out pressure limit or counter-clockwise to decrease it. Never turn the screw more than one revolution at a time. Additionally, be cautious never to adjust the cut-out pressure to a level higher than the maximum recommended setting. This causes the motor to draw excessive current and potentially damage it and the electrical system.

In the end, a little time devoted to service can make a big difference on not only compressor productivity, but also the entire operation. Knowing this, it’s best not to leave your compressor’s maintenance schedule up in the air.

Dan Leiss is president at Jenny Products ( Contact him at