Air compressor parts: about the things you will find on your compressor.

Keep your compressor in top condition, with our great articles on air compressor parts. Buy only the right stuff for your compressor.

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Looking for air compressor parts? Air compressors have of many parts that have to be serviced, can break or get  dirty. When you own an air compressor, or consider buying one, it’s handy when you know a little about the different compressor parts.Even when you don’t want to do any service or repair on the machine yourself, knowing just a little bit about the various part can help a lot when buying a compressor or when talking to the repair guy.Here’s an overview of the various air compressor parts you can find on your machine. Not all parts can be found on all types of compressors.

Compressor Air filters


Air filter biuld-up.
(Photo: Atlas Copco)

Air filters will protect your compressor from its number one enemy: dust. It’s one of

Save money! An air compressor with dirty inlet filter(s) will reduce the output capacity. You will pay more money through your higher energy bill than the cost of a new filter! This is one of the air compressor parts that you should keep an eye on!

More tips on compressor air filters here

Pressure switch

image of pressure switch of air compressor 

Typical air compressor pressure switch

Every compressor has some form of pressure switch. The pressure switch basically tells the compressor when to start and when to stop.

The air compressor pressure switch on small and older compressor is a completely mechanical device. With two set-screws you set the upper and lower pressure. On big and newer compressors, it’s probably a pressure sensor, with a separate controller with LCD-screen to read out the pressure and control the compressor.

More information about your air compressor
pressure switch

Oil filters


The Oil filter filters the compressor oil.

Oil filters are normally only found on bigger compressors like oil-injected screw compressors.

The (small) reciprocating piston compressors doesn’t have an oil filter. Lubrication is done by the splashing of the crankshaft in the oil bath.

Obviously, the oil filter is there to filter out any dirt from the oil. Dirt like sand, dust or small pieces of metal will wear-down rotating parts like the compressor element and the bearings.

The air compressor oil filter protects all moving parts like compressor element, bearings and valves from breaking down.

Read more about compressor oil filters.

Compressor oil

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Compressor oil.
Photo: Atlas Copco

Although it not really belongs to the ‘air compressor parts’, it IS part of the compressor: the oil.

Using the right oil for your compressor is very important. This is true for both rotary screw compressors and reciprocating piston compressors. Compressor oil can get very hot, up to 120 degrees.

Air compressor oil is designed to withstand these kind of temperatures.

Read more about air compressor oil.

Compressor valves

Compressors have different valves, all with a different purpose, I’ll list the most important ones:

Inlet / outlet valves on reciprocating piston compressors: these valves regulate the intake and exhaust of the piston compressor. They make sure that the air can’t flow back. They are mostly operated (opened/closed) by the pressure difference in the system (so, not mechanically like in your car).

Air compressor check valve: Check valves can be found in various locations. There are at least 2 check valves in your screw compressor. They are also found between your reciprocating compressor and the air receiver (tank).
This is to make sure that when the compressor is stopped, no air can flow back into the compressor.

Air compressor unloader

unloader valve rotary screw compressor

Unloader valve

There are two kinds of unloader valves in compressor world: a small one that can be found on (small) reciprocating piston compressors, and a big one that can be found on (big) rotary screw compressors.

The first one (on reciprocating compressors) is installed on the discharge line of the compressor. This one is often called a blow-down valve, because it blows-down the compressed air in the compressor discharge pipr when it stops.

Read more here about your air compressor unloader.

The second type is located on the air-intake of rotary screw compressors. When the set pressure is reached, the
compressor will go in ‘unload’ mode: the unloader valve will almost completely close the air intake of the compressor. For clarity reasons, I will refer to this valve as the inlet valve.

Read more here about your air compressor inlet valve (unloader) here.

Compressor cooler

compressor after cooler with condensate trap

After cooler with condensate trap. Photo: Atlas Copco

Every compressor has some sort of cooler. Why? When air is compressed, a lot of heat is generated (read: most of your expensive energy will be converted to heat, only 4% will be compressed air energy).

To get rid of all this heat, your air compressor has 1 or more coolers.

Small air compressors (the reciprocating piston type) have the simplest form of cooler: fins around the discharge pipe (the pipe between your compressor and the receiver/tank).

Bigger air compressors (of the rotary screw type) have normally 1 oil cooler and 1 after cooler. The oil-cooler will cool the hot oil before it is returned to the compressor element.

The after cooler will cool the compressed air before it comes out of the compressor.

Many times, both coolers are mounted next to each other, with one fan to blow cooling air through it.

Air compressor Motors

Most stationary and small moveable air compressors are powered by electro motors. Bigger portable compressors are usually powered by diesel engines. Very big compressors in large plants (like oil refineries) are sometimes power by steam turbines (both for safety and because steam is cheaper than electricity for them).

The electromotor used are just standard off-the-shelve electro motors. When you want to buy a replacement motor, always check the power (kW of HP) and the mechanical connections.

Some motors are connected to the compressor with a direct coupling. Others are connected using pulleys
and belts.

Air compressor pulley

The pulleys on the compressor and motor are usually not of the same diameter. There’s a so called drive ratio, which allows the compressor to turn slower than the electro motor (but with more torque). When ordering new pulleys, make sure that the outer size and the size of the shaft are the same.

Sometimes it’s necessary to renew the pulley together with the belts. To remove the pulley from the shaft, use a pulley puller (a special device, can’t do it without it).

To mount the new pulley back on the shaft can be tricky. If you notice that you can’t just fit it on there, the hole is too small (or the shaft is too thick). That’s normal. You need to heat up the pulley with some sort of torch (or oven). When it’s hot enough (when you spit on it and you spit starts ‘dancing’, it’s hot enough), slide the pulley over
the shaft in one smooth motion. Don’t stop, as soon as the hot pulley touches the cold shaft, it will lose heat and shrink (and the shaft will get hotter and grow).