How to use air efficiently

Compressors are found in many types of environments and used widely in maintenance work, DIY projects, construction sites and more. In this article we cover the different types of compressors.

Types of Compressors

When air is compressed and contracted in volume, it exerts a great force to return to its original state. This is called 'pneumatic energy' and can be used to move various equipment. A compressor is a device that can produce this compressed air. Compressors are classified into the following types according to the method of air compression and the structure of the compressor.

Compression Method Type

Compressors are classified into the following types according to the difference in air compression method.

Rotary compressors

Rotating rotors inside a casing continuously change the volume between the casing and the rotors, thereby compressing the gas.

Reciprocating compressor

This method compresses air by changing the volume in the cylinder through the reciprocating motion of a piston. The low-speed rotation makes noise and vibration louder, but the compressor is low-cost. Reciprocating compressors use this compression method.

Axial-flow compressor

Axial-flow compressors are capable of compressing air with high compression ratio and high efficiency. They are also called axial-flow compressors. As the structure of the compressor is very complicated, it has many parts and the price is very expensive. Axial compressors have the disadvantage of being prone to 'surging', a phenomenon in which the compressor stops working properly and stalls.

Centrifugal compressors

Like the axial-flow type mentioned above, this is a turbo type compressor. It is a compressor that converts kinetic energy by gradually decelerating air from the impeller (which provides torque) to the diffuser in a centrifugal direction. Compared to axial-flow compressors, this compressor is characterized by less reduction in compression efficiency due to downsizing. It is also very light and less expensive because its structure is simpler than that of an axial-flow compressor in terms of the number of parts. Surging is also less likely to occur, and the compressor can be used stably. The impeller of a centrifugal compressor is strong enough to withstand high pressure, but it is subject to strong centrifugal force and may fail due to metal fatigue.

Types of Lubrication Methods

There are three types of compressor lubrication methods: oil-injected, oil-free, and water-lubricated.

Oil-in type compressors

Oil-in compressors use oil for lubrication. Compressors must be lubricated in some way or the compressor will become damaged or burnt. Oil-filled compressors that use oil for lubrication generate oil mist in the compressed air.

Dry oil-free compressors

These compressors are lubricated without using any oil. No cooling or sealing material is injected. Therefore, oil mist is not generated as in oil-lubricated compressors.

Water-lubricated oil-free compressors

Water-lubricated compressors literally use water for lubrication, whereas oil-lubricated compressors use oil. Water is injected into the screw to cool the heat of compression and lubricate the inside of the screw with water. Since only water is used, compressed air contains no oil mist.

Types of Cooling Methods

When air is compressed by a compressor, the compressed air becomes hot and must be cooled. There are two types of compressed air cooling methods

Water-cooled compressors

This method uses water to cool the compressed air. The water-lubricated oil-free compressor mentioned above falls under this category.

Air-cooled compressors

This type of compressor does not use water, but instead uses a fan to create cooling air that cools the compressed air.

As discussed in this article, there are many types of compressors, depending on the method of air compression, lubrication, cooling, and various other classifications. When purchasing a compressor, select the compressor that best suits your application.