Oil Lubricated Air Compressor Technology

oil lubricated screw compressor installation

Lubricated Compressors

Lubricated compressors require oil to keep the production process running smoothly. They are reliable and efficient compressors that can be installed alongside a variety of air tools and accessories to maximise profitability and create an installation that works for you. Lubricated compressors come in a variety of types including lobe, screw, liquid ring, scroll and vane.

Oil can later be removed from the compressed air using a wide range of downstream equipment such as oil filters and dryers. This allows you to remove any contamination the air can even be cleaned down to 0.01 micron. This is great for a wide variety of industrial applications such as manufacturing, building work, waste management, quarrying, recycling and many other uses.

a pair of rotary screws for air compressor
A pair of screw rotors

What is a Rotary Screw Compressor?

One of the most popular types of oil lubricated compressors is the screw compressor. This type of compressor is a positive displacement compressor and is the predominant type in use today. The main screw compression element parts comprise of a female rotor and male rotor that move towards each other while the volume between them and the housing decreases. The pressure ratio of a screw is dependent on the length and profile of the screw and of the form of the discharge port.

The two rotors are usually designed with different profiles. The male rotor has convex lobes and the female rotor has concave cavities. This allows them to mesh together. The male rotor is normally designed with fewer lobes than the female rotor, this is so that it will rotate at a quicker speed, driving the female rotor.

The screw element is not equipped with any valves and there are no mechanical forces to create any imbalance. It can, therefore, work at a high shaft speed and combine a large flow rate with small exterior dimensions.

Main Parts and Functions of a Rotary Screw Compressor


These perform the core duty of rotary screw air compressors and the pair will be housed inside compression cylinders. The turning rotors trap a volume of air and compress it to a higher pressure as it moves through the rotor.

Electric motor

A compressor needs power, this comes from the motor. The motor is used to power the rotation of the male rotor, which subsequently drives the female rotor.


These are used to make sure rotors stay securely in the correct position. They are positioned on the ends of both rotors and ensure that the rotors are rotating evenly and remain balanced.

Suction and Discharge Valve

These valves control the initial gas retrieval and removal from the compressor. The suction valve opens to let air into the system and the discharge valve receives the pressurised air at the end of the process.

Oil separator filtration

Oil will need to be removed from the compressed air. An oil separator ensures that as much oil as possible is removed and returned to the compressor for lubrication, leaving the air clean and oil-free.Watch this video to learn more about how genuine parts play a critical role in the air / oil separation process in a CompAir air compressor.


This will allow you to control and operate your air system. The controller gives you the power to monitor the operational parameters of your system and ensure it is running effectively.

Delcos XL compressor controller
Delcos XL touchscreen compressor controller

Oil vs Oil Free

In an oil injected rotary screw compressor, oil is used for four main purposes. It is injected into the compression chamber to cool the machine, provide adequate lubrication of the moving parts, provide sealing and to aid with noise dissipation. The thermostatic valve also plays an integral role in maintaining the optimum temperature over a range of ambient temperatures by controlling the quantity of oil that is circulated to the oil cooler or the bypass.

To remove oil from the final product, the compressed air leaves the airend and is passed through to an oil separator. This will remove the majority of the oil through velocity changes. Coalescent filters can then be used to further reduce the oil quantity, resulting in a low oil carry over of around 2-5 ppm.

An oil free air compressor, on the other hand, does not use any oil in the compression cavities. The male and female rotors do not touch and their positions are maintained through lubricated timing gears that are outside of the compression chamber. This ensures that the air compressor output is completely oil free air. In water-injected oil free compressors, water is used instead of oil to perform the same duties such as cooling and lubrication.

Many businesses will opt for an oil free air compressor compared to oil lubricated compressors as oil-free designs provide guaranteed clean air.


COMPAIR lubricated screw installation



Lubricated Compressor Maintenance Tips


Use the correct oil

In injected screw compressors, oil plays an integral role. You should always ensure that you choose an oil that is the correct type for your installation. Genuine OEM oil is always the best choice as it helps to maintain the integrity of your system and keeps your compressor running smoothly and efficiently.

Check for oil and air leaks

Leaks in your system can drastically decrease efficiency and ultimately cost you money. Leak detection surveys can be carried out by expert aftermarket engineers who use ultrasonic leak detection technology to quickly and easily identify leaks in the system.

Regularly inspect the airend

Your airend should generally last around 44,000 hours if maintained correctly. Factors such as overheating, poor lubrication, condensation and corrosion can cause damage to the airend which may result in malfunction or breakdown. Regularly checking for any issues with the airend can help you to diagnose and fix a problem early on.

Check hoses regularly

Check your compressors hoses periodically to ensure they are not cracked or corroded, this could result in a leak which may reduce energy efficiency and ultimately cost you money.

Drain condensation from air receiver tanks

Regularly draining your receiver tanks will keep it clean and running smoothly. A build-up of moisture could be detrimental to your compressed air output.

Check and change air filters

If your air filter is not performing effectively, it may be allowing dirt and dust particles from the outside in. This will force your compressor to work harder to intake air. If you notice a build-up of dust, you may want to consider replacing your air filter.

Please watch this video to see the airend in action