Reciprocating Air Compressor is a positive compressor in which air is sucked in a chamber and compressed with the help of a reciprocating piston which is used by the compressor. It is called as positive displacement. Firstly air is sucked in a chamber and then compression air transfer to decreasing area by the piston. Which does the reciprocating motion is decreased by a piston?
The reciprocating compressor consists of a piston which is enclosed within the cylinder & equipped with suction & discharge valves.
The piston receives power through the crankshaft and connecting rod. A flywheel/belt wheel is fitted on the crankshaft which is connected by the electric motor or diesel engine. The uniform motion throughout the cycle of operations.
The compression air is first drawing a volume of air into the cylinder through suction valves during by the piston stroke. The compressing & discharging on the return stroke of the piston through delivery valves.
This working is used in every Reciprocating Air Compressor. You will easily understand compressor engineering from the below description.
The main three type of air compressor is used for industrial works:
1.) The Single Stage Reciprocating Air Compressor Works
2.) The Double Stage Reciprocating Air Compressor Works
3.) The three-stage air compressors works
Single Stage Reciprocating Air Compressor Works
The single stage reciprocating air compressor, the entire compression air is carried out by the single cylinder.
The compression air is affected in one end of the piston. The cylinder is known as single acting, the compression air is affected in both ends of the piston, the cylinder is known as a double acting reciprocating air compressor.
The opening & closing of a simple check valve depends upon the differential pressure, if mechanically operated valves are used for suction & discharge then their functioning is controlled by cams which are on the wheel.
The weight of air in the cylinder will be zero when the piston is at the top dead center at this position. When piston moving downwards, the pressure inside the cylinder in the atmospheric pressure & suction valve/inlet valve opens. The air is drawn into the cylinder through the filter element. This type of operation is known as suction stroke.
When the piston moves to upwards, the compressed air in the cylinder & inlet valve closes when the pressure increases to atmospheric pressure. This is compression stroke of a compressor. The end of this stroke discharge/delivery valve opens & air is transfer to a receiver. It is a double acting reciprocating air compressor. Suction stroke is starting the process at end of the piston. While at the same time working discharge stroke is the process for another end of the piston. We can say that suction & compression took place on both ends of piston & cylinder in double reciprocating air compressor.
Double Stage Reciprocating Air Compressor Works
In double stage or two stages, reciprocating air compressors consists of two cylinders. One is called a low-pressure cylinder and second is called a high-pressure cylinder.
When piston in a low-pressure cylinder is the outer dead center (ODC) the weight of air inside a cylinder is zero, as piston moves towards inner dead center (IDC) pressure falls below atmospheric pressure when suction valves open due to a pressure difference.
The atmospheric air is drawn into the low-pressure cylinder through air suction filter. Air is compressed by the piston and pressure inside & outside the cylinder is equal. When both are equal point suction then valves closed.
The piston moves towards ODC compression air took place and when the pressure of air is in a range of 1.5 kg/cm² to 2.5 kg/cm² then delivery valves opens & this compressed air is entered into a high-pressure cylinder by the intercooler. This is called low-pressure compression.
Both sides suction & discharge stroke took place of the piston then it is called Double Acting Low-pressure compression.
Suction valves of a high-pressure cylinder open when the air pressure in a high-pressure side is below to the receiver pressure & air from low-pressure cylinder drawn into the high-pressure cylinder.
As the piston moves towards the ODC, firstly stage air is compressed. When the air pressure from the low-pressure cylinder and inside the high-pressure cylinder is equal, then the suction valve is closed.
Now the air is compressed by the piston when the pressure in the High-Pressure Cylinder exceeds that of the receiver & discharge valves open. This high-pressure air is delivered to a receiver.
The Same process is repeated in every cycle of operation. Both sides of the piston suction & discharge stroke on the place then it is called double-acting high-pressure compression.
In double stage reciprocating air compressor, the pressure can be made in a range of 5.5 kg/cm² to 35 kg/cm².
Normally we required air pressure above 7.0 kg/cm² & delivery of air above 100 cubic feet/min. this type of pressure used in double stage reciprocating air compressor.
This is the most common popular model used in various types of engineering plants. If we required air pressure above 35 kg/cm², then the double stage reciprocating air compressor is not useful.
The three-stage air compressors.
Working Principle of Multi-Stage Air Compressor
Mostly industries required air pressure of more than 35 kg/cm² to produce their product. For example, a mineral water bottle requires air pressure more than 40 kg/cm². To produce the desired shape of a bottle at the bottom side and other fields in industrial.
In two stages reciprocating air compressor is not useful. We required the air compressor which produces air pressure above 35 kg/cm².
Air pressure is release when achieved by a multi-stage air compressor. Now use three stage reciprocating air compressors as a multi-stage air compressor. If we are required air pressure discharge above 85 kg/cm² then four-stage air compressors are useful.
The working rules or design of multistage air compressor is the same as double stage air compressor.
In the three-stage air compressor, fresh air from the atmosphere enters in the low-pressure cylinder. Air enters through a suction filter.
The air is compressed by piston up to 4 kg/cm² & then delivered to the second stage cylinder through intercooler compression. This type of stage suction and compression took place on both sides of the piston.
Now the second stage cylinder low-pressure air is compressed up to 14 kg/cm² & discharge towards the third stage (high pressure) cylinder through the second intercooler to achieve the air pressure up to the desired discharge pressure.
At high-pressure cylinder, the 14 kg/cm² air pressure is increased up to the require discharge range. In requiring a range from 35 kg/cm² to 85 kg/cm² by the piston reciprocating inside the high-pressure cylinder.
In this stage, suction and compression require both sides of the piston.
The multistage reciprocating air compressor is used in a few industries like Pet Blowing, CNG (Compressed Natural Gas) Center etc.
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