To select the best Air Compressor for engineering unit is a very important task. You have to use different compressors for different purposes. Hence air compressors are used for industrial purpose. There are some compressors used for medical purpose. Compressors can be used for refrigeration purpose also.
So, the two main classification of Air Compressor is
01) Positive Displacement Type.
02) Dynamic Type.
You will find details of each type from below description.
Positive Displacement Air Compressors
Positive displacement types compressor are those who mechanically displace a fixed volume of air into a reduced volume.
Compressor, when operated at a fixed speed, can deliver the constant volume. The discharge pressure is determined by the system load conditions.
If the consumption of air is more than discharge pressure falls below the cut-off pressure & compressor works on load condition.
Hence these types of Air Compressor further classified as
Reciprocating Air Compressor
In this type compressed air is generated by to & fro movement of a piston inside the cylinder (compression chamber). Hence each movement compresses a fixed quantity of free air at a specific pressure.
Single stage or double stage or multi stages and single acting or double acting is the further classification of Reciprocating Air Compressor.
A vertical type air compressor is used for the application of compressed air ranging in between 50 to 150 CFM. Horizontal balance type compressor is most suitable for application ranging from 200 to 5000 CFM.
Rotary Air Compressor
In this type, air is compressed by two rotating or inter meshing rotors. According to the type of construction Rotary Compressor can be further classified as
(a) Rotary Screw Compressor
(b) Rotary Vane compressor.
Air is compressed between two rotating screws (male & female screw) and casing. So, the compression took place in gradually reducing space between these two parts.
(b) Rotary Vane Compressor
Air is compressed between casing & rotating rotor by the help of movable rotor blade. This type of air compressor can be further classified as a single stage or double stage rotary air compressor.
Dynamic Air Compressors
The dynamic type air compressors mechanically impart velocity to the air. The impellers rotating at a high speed, in an enclosed casing, produce this action.
The air is forced into a progressively reduced volume. The volumetric flow will vary inversely with the differential pressure across the compressor. This type of compressor is further classified as
(a) Centrifugal Air Compressor
(b) Axial Flow Air Compressor
(c) Roots Blower Compressor.
Centrifugal Air Compressor
In a centrifugal air compressor, an impeller is mounted on a shaft and positioned within the housing. It is consisting of an inlet duct, a volute, and also a diffuser.
The velocity of the air can be imparted by the high-speed rotation of the impeller. Hence the diffuser surrounds the impeller and acts to convert the kinetic energy of air into potential energy at a higher-pressure level.
Axial Flow Air Compressor
The axial flow type air compressor is essentially a large capacity, a high-speed machine with characteristic quite different from the centrifugal air compressor.
Each stage consists of two rows of blades, one row rotating & the next row of the blade is stationary. The rotor blades impart velocity and pressure to the air as the motor turns, So, the velocity is converted to pressure in stationary blades.
Roots Blower Compressor
This type is generally called as a blower. Hence the discharge air pressure obtained from this type of machine is very low.
In the single stage, only one bar discharge pressure can be obtained and only 2.2 bar pressure is obtained from the double stage.
So, the discharge pressure achieved by two rotors, which have separate, parallel axis and rotate in opposite directions. Hence this is the example of positive displacement compressor in rotary type air compressor.
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