Basic compressor maintenance will ensure efficient operation for years to
By Dan Leiss, President Jenny Products Inc.
In today’s manufacturing environments, compressed air is often regarded as an
important means towards completing everyday tasks. Used to power various tools
and equipment, compressed air is essential to the daily operations of these
Considering how valuable compressed air is, keeping the compressors well
maintained should be a high priority. Nonetheless, preventative maintenance can
easily be overlooked during the hustle of the workday, or some may think there
is just not enough time to dedicate to a maintenance schedule. But it doesn’t
have to be a complicated, time-consuming process. In fact, simply incorporating
several small day-to-day tasks into a preventative maintenance routine can make
a difference in the life and repair cost of an air compressor. These checks only
take a few minutes, but they can add months — or even years — to the service
life of a machine.
First, always begin with a clean compressor. While clean equipment looks better,
it also will help improve maintenance since it will make it easier to detect
leaks and broken or loose components. Next, move into the following preventative
maintenance checks to help keep a compressor running strong for years to come.
While a number of things should be checked before each compressor use, these
daily maintenance tasks are among the quickest and easiest to perform. For
starters, 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 also tighten any loose nuts or bolts. Look
over the controls, gauges, accessories and instruments, making certain there are
no loose mountings or damage.
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.
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. A standard filter will trap dust particles based upon micron size,
while a coalescing filter will remove water and oil from the air. For some
applications, such as spraying paint, an air dryer should be used with the
coalescing filter so that all moisture is removed from the lines. On the other
hand, some tools function better with some moisture. When using a nail gun, for
instance, an operator may want to add oil to the line with a lubricator.
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.
the end of each day, if not more frequently, drain condensation from the air
tanks. As always, begin by disconnecting the power source. 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 also 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
While a number of small maintenance tasks should be done daily, several others —
while still important — can be performed less often. For instance, 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 also should be checked monthly for leaks,
which could cause a number of problems. 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
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 is another potential problem an operator may experience.
This 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.
To fix many of these problems, it’s typically a matter of cleaning, or possibly
replacing, the affected part. 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
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.
While neglecting the air filter and lubrication system tends to cause the most
problems, there’s always a chance of a compressor needing some extra care. Any
compressor that’s well taken care of shouldn’t require any adjustments, but many
compressors tend to be used and abused nonetheless. If the unit over-pressurizes
or fails to provide enough pressure, the problem could be with the pilot valve
cut-out pressure adjustment. Begin by cleaning any dirt from the valve seat,
then adjust the valve according to manufacturer specifications, which are often
available online. Typically, this involves turning the outermost screw on the
pilot valve clockwise to increase the cut-out pressure limit — the point at
which the pressure stops building — or counter-clockwise to decrease it. Never
turn the screw more than one revolution; it could cause the screw to burst out
due to the tank pressure. Additionally, be cautious to never adjust the cut-out
pressure to a level higher than the maximum recommended setting. This will cause
the motor to draw excessive amps and potentially damage the motor and electrical
system. Besides, the time spent on a compressor should be used to maintain or
improve performance, not damage it.
To change the point at which the compressor cuts in, or comes on, when system
pressure begins decreasing, adjust the pressure differential screw similarly.
Despite the ease of this adjustment, it’s rarely necessary.
The pressure switch is set by the manufacturer, but there are some cases in
which an operator may benefit from adjusting it to a lower pressure range. If
the compressor is being used with air tools that all require a maximum pressure
of only 90 psi or less — and the compressor normally kicks in at 105 psi and
shuts down at 125 psi — the pressure can be lowered to an 80 to 100 range, which
will still provide adequate pressure yet will reduce wear on the machine. The
pressure range can be adjusted while the compressor is running by turning the
pressure range screw clockwise to increase overall system pressure, or
counter-clockwise to decrease it.
In the end, just a few minutes a day and some monthly preventative maintenance
checks could make a big impact on a compressor’s performance and service life.
In fact, following the manufacturer’s guidance just might cause any potential
compressor problems to virtually vanish into thin air.