The discharge pressure
The pump is overheating
and causing the air ﬁ lter
The air compressor unit is
making excessive noise
(a knocking sound).
There is a large quantity
of oil in the discharge air.
NOTE: In an oil lubricated
compressor there will
always be a small amount
of oil in the air stream.
There is water in
discharge air / tank.
The pressure switch does
not release air when the
unit shuts off.
□ The air demand exceeds the pump
□ The air intake is restricted.
□ There are air leaks in the ﬁ ttings,
tubing on the compressor, or the
plumbing outside the unit.
□ There are blown gaskets.
□ There are leaking or damaged
□ The insulating gasket between the
ﬁ lter and the head is missing.
□ There are broken valves / blown
□ The motor pulley or the ﬂ ywheel is
□ The fasteners on the pump or the
motor are loose.
□ There is no oil in the crankcase.
□ The connecting rod is worn.
□ The piston pin bores are worn.
□ The piston is hitting the valve plate.
□ There is a noisy check valve in the
□ The piston rings are worn.
□ The compressor's air intake is
□ There is excessive oil in the
□ The oil viscosity is wrong.
□ This is normal during operation.
The amount of water increases with
□ The unloader valve on the pressure
switch is malfunctioning.
□ Reduce the air demand or use a compressor with more capacity.
□ Clean or replace the air ﬁ lter element.
□ Listen for escaping air. Apply soap solution to all ﬁ ttings and
connections. Bubbles will appear at points of leakage. Tighten or
replace leaking ﬁ ttings or connections. Use pipe thread sealant.
□ Replace any gaskets proven faulty on inspection.
□ Remove the head and inspect for valve breakage, misaligned
valves, damaged valve seats, etc. Replace defective parts and
reassemble. Install a new head gasket each time the head is
□ Install the gasket.
□ Replace the valves or install the new gasket.
□ Tighten the pulley / ﬂ ywheel clamp bolts and the set-screws.
□ Tighten the fasteners.
□ Check for proper oil level; if the oil level is low, check for possible
damage to the bearings. Dirty oil can cause excessive wear.
□ Replace the connecting rod. Maintain the oil level and change the
oil more frequently.
□ Remove the piston assemblies from the compressor and inspect
for excess wear. Replace the excessively worn piston pin or
pistons, as required. Maintain the oil level and change the oil
□ Remove the compressor head and the valve plate and inspect for
carbon deposits or other foreign matter on the top of the piston.
Replace the head and the valve plate using the new gasket. See
the Lubrication section for the recommended oil type.
□ Replace the check valve. Do not disassemble the check valve with
air pressure in the tank.
□ Replace with new rings. Maintain the oil level and change the oil
□ Clean or replace the ﬁ lter. Check for other restrictions in the
□ Drain oil down to the correct full level.
□ Only use Mobil 1
□ Drain the tank more often. At least daily.
□ Add a ﬁ lter to reduce the amount of water in the air line.
□ Replace the unloader valve if it does not release the pressure
for a short period of time when the unit shuts off. Do not disas-
semble the check valve with air pressure in the tank.