Compressor Basics : twin pot versus twin stage

[Richard T]

When looking at compressors I see some single and some twin cylinder. The twins have two pistons/cylinders, arranged in a ""V. Looking closer it's apparent that some of those are "twin pot" designs where the motor/crank is simply driving two pistons in cylinders of the same size, and they're both pushing air through a one-way valve into the tank, so look like this (it's an old example but shows the idea) :

...and others are "twin stage" where the two cylinders are different sizes, one small one large, and the larger one does a first stage of compression and pushes that air into the second cylinder, which has smaller cross-section and pushes the air up to a higher pressure, and then into the tank. They look like this :

Are these intended for slightly different tasks / usages ? It seems that the twin-stage would be good if you wanted really higher-pressure air, whereas the twin-pot would provide a higher volume but at a more 'normal' set of pressures - but I might just be reading things into this. Any preferences or thoughts on which is better for regular workshop use (spraying / air tools / small blast cabinet etc) ? or is there no real difference and they're just different ways of achieving the same results ?

 

[hotponyshoes]

Pretty much as you have worked out,
Either higher pressure or higher flow rate so just match your requirements to the type you need.

Aside from any sort of shot blast cabinet, even small ones draw a huge amount of high pressure air.
I have one that is big enough to get a 20" alloy wheel in. 2x twin pump 4hp compressors just about keep up with it providing nobody else wants to use the airline at the same time.

 

[carbon]

Two stage air compressors are supposed to be more efficient than single stage as there is a cooler between the two stages so the air is cooler when it gets to the second cylinder. It’s difficult to see in your second picture but the pipe work that connects the two cylinders is in the the air flow from the pulley

 

[brightspark]

a twin stage compressor is more efficient. the larger piston compresses a large amount of air in to the smaller barrel and the smaller piston can push the compressed air in to the tank at a higher pressure with less effort

 

[addjunkie]

Two stage air compressors are supposed to be more efficient than single stage as there is a cooler between the two stages so the air is cooler when it gets to the second cylinder. It’s difficult to see in your second picture but the pipe work that connects the two cylinders is in the the air flow from the pulley

Interstage cooling reduces the volume of air going into the second stage by removing the temprature, therefore the second stage is more efficient as its compressing cooler air taking up less volume, so you can get more in, also means the discharge temprature isnt so high consequently reducing material qualities required to build it.