#Technical studies – Study 17
A pneumatic compressor is a device that takes in air as input at a certain pressure, processes that and provides the compressed air at a higher pressure.
Types of pneumatic compressors:
The compressors are divided into three types
- Reciprocating piston compressors
- Rotary piston compressors
- Flow compressors
Reciprocating piston compressors are divided into two types
- Piston compressors
- Diaphragm compressors
Rotary piston compressors are divided into three types
- Sliding vane rotary compressors
- Two axial screw compressors
- Roots blowers
Flow compressors are divided into two types
- Radial flow compressors
- Axial flow compressors
Reciprocating piston compressors:
These types of compressors are most commonly used compressors. They have a broad pressure and delivery ranges. These compressors are available in three types- single stage, double stage and multi stage. Single stage compressors can deliver up to a pressure range of 4 bars. Double stage compressors have a pressure range of 15 bars and for multi stage compressors the pressure range are 15 bars. Though double stage and multi stage compressors have same pressure ranges multi stage compressors are used for high pressure requirements with inter cooling system in both stages.
Diaphragm compressor is the type of reciprocating piston compressors. In this the piston is separated from the suction chamber by the means of a diaphragm. This configuration keeps air away from the reciprocating parts; in result the air is free of the oil. As the air is oil free, this compressor is used in food industries, chemical industries and medical industries.
Rotary piston compressors:
As the name, the pistons in this machine rotate.
Sliding vane compressor:
These types of compressors have a smooth operation compare to reciprocating piston compressors, but not able to compress at high pressures as multi stage compressors. They have sliding vanes in their rotors in the form of slots and these slots seem like chambers with the cylindrical wall. While rotating these vanes are forced toward the wall and their sizes are increased or decreased. These rotating parts compress the air and create pressure.
Advantages of sliding vane compressors:
- Quiet running
- Compact dimension
- Smooth air delivery
Two axial screw compressors:
This compressor has two screws –one is concave shape and the other one is convex shape. Air can enter inside the compressor only when the screws are rotating. The entered air then compressed and delivered to the outlet.
This machine is also called wet rotary screw compressor, because oil is supplied to inlet with the air to reduce the friction between screws. Later the oil is separated by the oil separation unit.
This compressor is also called Lobe compressor. They have the capacity to deliver the air at high volume. They have very limited pressure capacity, because there is leakage in rotors and in the housing. The application that requires a high volume, low pressure positive displacement compressor, there this compressor is used.
Flow compressors are also known as turbo compressors. They are famous for delivering high volume compressed air by increasing the stage pressure. But there is a small increase in pressure that is about 1.2 times of the inlet air pressure per stage.
These are available in two types –axial and radial.
Axial flow compressor:
This type of compressor has a set of rotating blades. Air flow occurs in an axial direction that accelerates the blades. These compressors produce compressed air at high volume and low pressure, less than a bar.
Radial flow compressors:
In this type of compressors air flow occurs in different chambers radially towards out. Then air returns to the main shaft and from there it flows outwards.
Compressor selection criteria:
The amount of air that a compressor delivers is the delivery volume. Before selecting a compressor we need to know the amount of volume that system requires.
The pressure that a compressor provides in output is known as working pressure.
The pressure that required by the operation is the operating pressure.
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