# What type of air blower/compressor to use?

I need a way to move air which is somewhere in between a compressor and a fan: something along the lines of 20-40 cfm at 2-3 psi (500-1000 liters/minute at 10-20 kPa).

Typical small compressors (of the right power rating) seem to be approx 0.5 cfm at 30 psi. Typical centrifugal blowers are approx 60 cfm free flow but only 0.05 psi max static pressure.

I'm having trouble visualizing what I need, let alone sourcing it. Leaf blower? Shopvac? Supercharger? Do I want a piston pump, diaphragm pump, screw compressor, turbopump, some type of higher pressure centrifugal fan, or ???

For this application energy efficiency at the described operating point is most important; size/cost/noise is much less important. UPDATE It also needs to be oil-free.

• Tough (at least for me) can you state the exact application, then we can look for what is usually needed there. If all else fails a dozen diaphragm pumps in paralell.
– mart
Apr 19 '17 at 10:31
• What demand - is it 20-40 cfm for 10 seconds, 1 minute, 1 hour or continuous as possible solutions vary. Apr 19 '17 at 12:34
• Check out regenerative blowers - along the lines of McMaster Carr part number 1010K22 Apr 19 '17 at 15:50
• @SolarMike It's several hours to continuous. Thanks! Apr 19 '17 at 20:47
• @mart The type of application is probably closest to a fridge compressor, but not with freon. Apr 19 '17 at 21:42

If efficiency is important, I would not compress to a higher pressure, then expand the air. I think the pressure ratio is in the right range for a positive-displacement pump, like the ones that are used in superchargers. There's an efficiency map here: https://en.wikipedia.org/wiki/Roots-type_supercharger

I think fans are out, as you won't get your combination of flow rate and pressure. The only thing you might want to look at is multistage fans. For this answer I'll concentrate on PD compressors. All of the following should be available in oil-free versions:

Side channel compressors come in the flow rate and pressure region you want. You will need to talk to an application engineer of a vendor to see if they fit your particular aplication. I don't know how they compare in terms of efficiency.

All rotary lobe compressors and sliding vane compressors I found with quick googling where designed for higher pressures or flow rates. If you find one in the right pressure range, talk to the vendor if the flow rate can be adjusted with a VFD.

Membrane pumps are built for lower flow rates. If all else fails, get ten or twelve, pumping in paralell into the same pressure manifold.

To perform the amount of mechanical work described here, it would take about $330W$ of power, if you consider the maximum pressure and airflow.

$$Power = \Delta P \cdot Q$$

This is assuming 100% efficiency, which will never be the case. Does your power budget allow this?

• Yes, a few hundred watts is okay. It's more about the % efficiency than the absolute power. Most of the blowers I've seen are only around 30% power efficient though... I think rotary lobe blowers lose power due to slip and centrifugal ones due to turbulence. I would guess a very large piston or bellows running at a very slow speed may be the most efficient, but nobody seems to make anything like that. May 3 '17 at 3:22

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