Compressor - one-stage versus two-stage?

[charlie95]

compressor -- one-stage versus two-stage?

whats the difference between a one stage compressor and a two stage compressor?
And why do we sometimes use a two stage compressor and not a one stage compressor ?

 

[Studiot]

This sounds like a homework project.

What have you already found out?

 

[charlie95]

This sounds like a homework project.

What have you already found out?

this is not a homework project.
I think the difference between the two is the temperature. With a two stage compressor
you can get a higher pressure, because after the first stage you have a cooler that lower the temperature, before it enters the second stage. If you just have a one stage compressor, the temperature will increase maybe over the specification of the pipeline, or maybe the compressor will overheat.

 

[sophiecentaur]

Also, there's the simple factor of the limited compression ratio of just one compressor stage. If you can dish out air at a higher pressure to the next stage then the final pressure can be (almost) the product of the two stages. Cooling the air between stages and after the final stage will give a significantly higher resulting pressure, of course. Diving bottles are (used to be) kept in a water bath whilst being filled, for that reason.

 

[Jobrag]

If you are talking about a centrifugal compressor there are limits on the pressure ratio you can achieve with a single stage.

 

[jim hardy]

I think the difference between the two is the temperature.

you are correct.
Find an old copy of Marks' Mechanical Engineer's Handbook, or Machinery Handbook.
It cautions against trying to operate single stage compressors above 100 psi because of the fire hazard to surrounding buildings.

We had some mis-applied compressors in my plant, single stage set to unload at ~120 psi.
I watched them struggle to make that last twenty psi with the temperature gage in outlet hovering around 410 degrees F. They continually burned up exhaust valves and piston rings.

Air compressor oil has high temperature capability - you shouldn't use ordinary engine oil in your little 125psi home reciprocating compressor.

 

[charlie95]

you are correct.
Find an old copy of Marks' Mechanical Engineer's Handbook, or Machinery Handbook.
It cautions against trying to operate single stage compressors above 100 psi because of the fire hazard to surrounding buildings.

We had some mis-applied compressors in my plant, single stage set to unload at ~120 psi.
I watched them struggle to make that last twenty psi with the temperature gage in outlet hovering around 410 degrees F. They continually burned up exhaust valves and piston rings.

Air compressor oil has high temperature capability - you shouldn't use ordinary engine oil in your little 125psi home reciprocating compressor.

ok. Do a two stage compressor use less KW(kj/s) than a one stage compressor then?
But are you sure that the temperature has something to with the outlet pressure?
Is it not only depending on the molweight of the gas.. higher molweight, the higher pressure... or higher inlet pressure->higher outlet pressure..??