Rotary Screw Compressor Working Principle-The Basic Parts & Functions

Rotary Screw Compressor Mechanical Functions

​A rotary-screw compressor is a kind of gas compressor like an air compressor. The rotary screw compressor working mechanism is based on a rotary-type positive-displacement. They are ordinarily used in place of piston compressors where great volumes of high-pressure air for large scale industrial use are required.

Also, it can be of great importance where high-pressure tools like impact wrenches and jackhammers are in use. Rotary screw industrial compressors are ideal for large-scale industrial application since they are more efficient and can run non-stop.

Besides, rotary screw compressors are usually quieter and produce lower temperatures as compared to other sorts of compressors. Lastly, rotary screw compressors give a constant supply of air power for a wide range of essential applications.

If you are new to compressors, you may still have difficulties differentiating the reciprocating and rotary compressor at a glance. For a reciprocating compressor, a piston builds a vacuum with the help of a pressurized movement inside the chamber.

In a rotary screw compressor, rotors are used to pressurize the air. To help you further, in this article, we shall discuss the rotary screw compressor parts and functions.

​The Basic Parts of a Rotary Screw Compressor:

Just like any other model, the screw air compressors also have different parts that are important for the application for industrial uses. Essentially, you will find rotary compressors of a distinct model, size, construction and performance. However, rotary screw compressor generally consists of the following basic parts


For a rotary screw, nothing can really work without rotors. The movement of the two rotors directs the air via a sealed series that helps in pressurizing the air molecules. With that, the air is converted from the thin ambient air of the environment and into a different pressurized force that can be applied for distinct industrial uses.

Integral Housing

The integral housing is meant to prevent the chances of leaks by keeping the air in tight. For a rotary screw compressor, the housing gives an air-tight section meant for air end purposes that aids in the compression process.

Within this integral housing, the rotors always move alongside each other to pressurize the confined ambient air and remove essentially all the moisture and oil contents. Actually, the tightness of the housing is quite important as it enables quick transfer between the inlet valve (where the ambient air gets into the compressor) right to the intended output.

O-Ring Seal

This is a ring that is fit on the inlet valve (point of entrance for the ambient air) to prevent leakage of the incoming air. It increases efficiency of the compressor.

Thrust Bearings

Ideally, producing compressed air from ambient air is an excellent engineering process. This is made possible by the thrust bearings that make the inner parts of a compressor to move with suitable consistency.

Inlet Bearings

Normally, a suction process is necessary for this type of compressor to let in ambient air to pressurize. With the help of the inlet bearings, the inlet valve is able to work effectively ensuring that the air is pulled in from the environment.

Basically, the inlet bearings ensure the air is let in continuously at reliable speeds during the operation time for the rotary screw compressor.

Shaft Seal

Like the inlet, the shaft has to be designed such that there is leakage. It should keep the air inside until the pressurization process is done for a specific round. An air-tight shaft seal will make sure that there is no air leaking to the outer part of the air compressor. With that, there will be a constant and efficient process for the air screw compressor.


Usually, air-bound oil particulates are present in any environment. Thus, the ambient air that enters the rotary screw compressor will surely have a certain amount of oil. This is true for water found in the air we always breathe.

Nevertheless, moisture and oil are undesirable for processes that entail drying, cleaning, painting and sanding. Luckily, the use of Sump in the rotary screw compressor ensures that ambient air is transformed into a desirable clean and compressed air.

Inlet Valve

The inlet Valve is a small flap that absorbs ambient air. The sucked air is then pressurized by the rotors then changed into a source of power for machinery and pneumatic tools. During the process of transformation, a number of activities take place in the inlet valve thus producing the compressed air.

Outlet Valve

Reasonably, the pressurized air needs to be let out of the system without any leakage to maintain its temperature or volume. To achieve this, a tightly bound outlet is necessary to direct each round of the compressed air right to the tubes that joins to the end-point tools. This precisely what the outlet Valve is meant for.

​How Does a Rotary Screw Compressor Work?

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Inside the air compressor, we have two helical rotors in the housing that interlock. The inlet valve will let in ambient air into the compressor. At this point, the air will be trapped between the two rotors. After this, the screw will turn, resulting in an increase of the pressure of the air due to the reduction of its volume

There are some rotary screw air compressors that come with just one screw. This type is not so much common in the industrial field, where the complete power like that of two screws is important for large-scale tasks. Normally, single-screw rotary forms are more often applied in refrigeration.

Generally, the design of a rotary screw air compressor entails housing and rotors. This kind of design is called air end. For all kinds of rotary compressors, the air end is the part in which the ambient air (incoming air) is compressed.

The Oil Rotary Screw Compressors.

Other rotary screw compressors utilize oil while others don't. Nevertheless, all compressors have to filter out the oil available in ambient air. For rotary screw compressors that utilize oil, the motor spins the male rotor which subsequently drives the female rotor.

Here, the oil creates a layer between these two rotors and further works as a coolant and sealant for the compressor's compression chamber.

​The Oil-Free Rotary Screw Compressors.

For oil-free compressors, no oil is applied to initiate the compression process. In this type, the two rotaries are managed by gears. In the absence of oil to work as a chamber sealant, such compressors may not be able to reach great levels of pressure.

Due to lack of cooling oil, Oil-free rotary screw compressors become hotter. Therefore, oil-free types are less effective compared to their oiled equals.

Because of such disadvantages, oil-free rotary screw compressors are often limited to some specific applications. Although they are uncommon, we have some oil-free models that utilize water rather than oil as a coolant.

Apart from the compression of air, the air end also helps in proving space for compression of air. After the completion of the air end stage, the freshly compressed air is passed directly to the sump (also called the separator tank).

From here, oil is removed from the air. The extraction of oil from the air is attained through a pinning process that thoroughly shakes the oil crudes from the compressed air for the air to be pure as it gets to the end as the final product.

Further, the oil separation process is facilitated by baffles. After the air has crossed the separator tank, it goes through a cooler then to the last point. This will always occur both for the case of an air-powered machine or a pneumatic tool.

In the process of air compression, the temperature of the freshly separated oil matters. In fact, a thermostatic valve will treat the oil accordingly. The reason here is to prevent the oil from becoming either cold or hot.

In case the oil becomes hot, it will sear and consequently wear down the internal parts of the machines. On the other hand, if it becomes cold, there will deficiency of temperature necessary to isolate it from all the water removed from the air in the process of compression.

During the air compression process, the air is not let into the system until it has sufficient pressure to be self-lubricated. In case the oil has a lot of water, the air end will not work well.

​Rotary Screw Compressors​ With a Fixed Blade

For this type of compressor, the driving shaft normally has an eccentrically supported roller in the pump section. In the chamber, the blade bisects the outlet and inlet valves. In this case, the blade itself is restricted by the interior body of the compressor and the roller surface.

In the compression process, the roller moves and the blade moves in an up and down motion to the rotary movement. In the exact sense, the compressor is made up of three moving parts- the roller, the shaft and the blade. Each of the parts is oiled.

Inside the cylinder, the steam of pressure and low temperature are compressed to high pressure and temperature. Thanks to the motion of the roller. All this process leads to the end product- the compressed air.


Understanding the parts and working principles of any machine is paramount. This goes a long way in ensuring that you are buying the right tool for the right task. Furthermore, it will help you when it comes to its maintenance. Hopefully, this article has enlightened you regarding rotary screw air compressor.

Read more: Vilter Screw Compressor

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