In this article, we learn what is air compressor, the applications of air compressors, and type of air compressors.
What is Air Compressor?
In various industrial applications, compressed air is required, A device or machine providing air at high pressure is called as air compressor.
An air compressor takes in air at atmospheric pressure, compresses it and delivers the high pressure air to a storage vessel called as receiver.
From receiver compressed air may be conveyed by the pipe-line to a place where the supply of compressed air is required.
Applications of Air Compressor
Compressed air is used in various industrial applications some of which are as follows:
It is used to operate pneumatic drills, air motors, hammers, riveting and nut tightening, etc.
Cleaning of workshops and automobiles.
Supercharging of I.C. engines and gas turbine power plants.
In paint industries for spray painting.
In the refrigeration and air-conditioning industry.
Construction of roads dams, tunnels, bridges, etc.
For spraying fuel in high-speed diesel engines.
For driving mining machinery.
For conveying sand materials, concrete, etc.
For operating air brakes.
In paper industries and printing machinery.
Type of Air Compressors
The type of compressors may be classified as follows:
1. According to the type of motion
a) Reciprocating air compressors: In these compressors, the air is compressed by the reciprocating action of a piston in a cylinder. It provides high-pressure air with intermittent discharge.
b) Rotary air compressors: These compressors have rotating elements to compress the air. It provides the air at low pressure but in large and continuous quantities. These compressors are further classified as follows:
Positive displacement compressors: These compressors have two sets of mutually engaging surfaces. Air is trapped between these lobes and squeezing action takes place. For example Roots blower, vane blower, etc.
Non-positive displacement compressors: In the compressors, kinetic energy is converted into pressure energy by the arrangement of the impeller and fixed rings. For example Centrifugal compressor, axial flow compressor, etc.
2 According to the number of stages
a) Single-stage compressor: In these compressors, the air is sucked and compressed in a single cylinder.
b) Multi-stage compressor: In these compressors, the air is sucked and compressed in two or more cylinders. Generally, the number of stages is equal to the number of cylinders.
3. According to the working position (side) of the piston
a) Single-acting compressors: In these compressors, the air is sucked and compressed on one side of the piston.
b) Double-acting compressors: When suction and delivery of air take place on both sides of the piston then it is called a double-acting compressor. It handles double the air than a single-acting air compressor.
4. According to the discharge pressure
a) Low-pressure compressors: Delivery pressure is less than 10 bar.
b) Medium pressure compressors: Delivery pressure is between 10 to 80 bar.
c) High-pressure compressors: Delivery pressure is greater than 80 bar.
5. According to the capacity of the compressor
a) Low capacity compressors: Discharge capacity is less than 0.15 m.-3/s.
b) Medium capacity compressors: Discharge capacity is between 0.15 to 5 m 3/s.
c) High capacity compressors: Discharge capacity is greater than 5 m Vs,
Reciprocating Air Compressor
The figure shows the principal parts of a reciprocating air compressor, which is a single-stage and single-acting type.
In these Compressors, the crank is connected to the prime mover or electric motor.
The Inlet and outlet valves are opened and closed by the pressure difference on both sides of the valves.
The operation of the reciprocating compressor is divided into two strokes that is suction stroke and delivery stroke.
During the suction stroke, the piston moves downwards due to which pressure in the cylinder falls below atmospheric and the inlet valve opens, and the air is sucked.
During a delivery stroke, the piston moves upwards with the compression of air in the cylinder. At that time, both inlet and delivery valves are closed.
At the end of this stroke pressure increases above the receiver pressure, hence delivery valve opens and the air is discharged to the receiver. (Receiver is a vessel that acts as a storage tank).
These pumps are widely used in industries and agriculture. They are suitable for high-pressure heads with low flow rates.
Terminology of Air Compressor
1. Free air delivery (F.A.D)
It is the volume of air delivered under the conditions of pressure and temperature existing at compressor intake. Generally, it is considered as 1.01325 bar pressure and 15 °C temperature.
2. Power capacity
It is the quantity of the free air actually delivered by the compressor in meter cubes per minute or meter cube per second.
3. Pressure ratio
It is defined as the ratio of outlet or discharge pressure to inlet or suction pressure.
4. Shaft power/Brake power
It is the power required to drive the compressor or it is the power delivered to the compressor shaft.