Single Stage, Two Stage and Three Stage Piston Air Compressors

Some common questions:- 

• How to know whether your Piston Air Compressor is a Single Stage, Two Stage or Three Stage machine by just looking at it? 
• Difference between Single Stage, Two Stage and Three Stage machines Piston Air Compressors. 
• What do you mean by Stages in a Piston / Reciprocating Air Compressor?

Stages of Compressor means that in the machine how many stages of compression that a particular air molecule or a set of molecules has to go through. If air is sucked in by one piston and then directly sent to the tank / air receiver through a pipe is a single stage machine. But if air is sucked in by one piston and then sent to another piston through interconnecting pipes or otherwise then this is a two stage machine.

In a Single stage machine a single piston has to develop the desired pressure generally around 9 bar (g) is maximum what a single stage machine can develop. In a Two Stage machine the total pressure of say around 12 to 25 bar (g) has to be developed by a total of 2 pistons. In such a situation the compression ratio gets divided among the two pistons. The maximum pressure that usually a two stage design can develop is around 25 bar(g) but that too after thorough engineering calculations, please note that not all two stage piston air compressors can develop 25 bar (g).

Single Stage machines usually come in 1, 2 or 3 pistons. You will notice that all the pistons have their own suction inlet filter and the diameter of each piston will be exactly the same. Above pictures are example of single stage machines.

Two stage machines usually come in 2 or 3 piston arrangement  (Never a single piston). In a 2 piston arrangement you will notice that the suction filter is on only 1 piston and the diameter of this piston is bigger than the diameter of the second piston. The diameter of the second piston becomes smaller because the compression ratio has to increase. Something like shown in this picture below.

In a 3 piston arrangement, there will be 2 pistons which will have their own suction filters and the diameter of these pistons will be exactly the same and they will send the air to the third piston which will be of smaller diameter. Something like shown in this picture.

Even three stage compressors are available where the pressure that needs to be developed is above 30 bar. Usually pet bottle blowing industry use these kind of machines. Like the below picture.

300 bar options are also available in three stage machines. Usually breathing air compressors for underwater diving / deep water diving need these kind of machines.

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