You don't need a two stage compressor to serve a blast cabinet. You need appropriate capacity in cubic feet per minute (cfm) at about 100 psig minimum, usually. A single stage compressor can easily do the job if it has enough piston displacement. Personally, I would want a minimum of about 15 cfm as a reasonable capacity for a blast cabinet. A lesser amount can be made to work, but would require a small nozzle and take a longer time, even for relatively small parts. Blasting is one of those cases where bigger really is better.

A single stage compressor compresses air in one shot from atmosphere to a maximum of about 135 psig. Higher pressures are usually not practical in single stage because of the very high temperatures involved. They are caused by the higher compression ratios needed to go higher in pressure in a single step. For example, the compression ratio in a single stage operating at 135 psig is about 10:1.

A two stage compressor compresses air in two stages. In reality, it is like two single stage compressors run in series, with the second one being smaller in displacement than the first one. The first stage compresses air to some intermediate pressure, usually about 40 psig maximum. Then the air is cooled by an intercooler (usually a length of finned tubing) and sent to the second stage where it is increased in pressure, usually to a maximum of 175 psig. The compression ratios when operating at 175 psig are about 3.5:1 for each of the two stages. Because of the higher maximum operating pressure, more air can be stored in the same sized tank than a single stage unit. This would have the result of increasing the usage time between motor starts for any common consumption rate.

Two stage units are a little more efficient in the HP required for a similar capacity and provide cooler air at similar pressures to single stage units, mainly because of the interstage cooling that takes place. If you have to work a single stage unit hard without some kind of dedicated aftercooler, the higher air temperature will result in less effective condensation and removal of moisture, especially in hot, humid weather. This can be a problem for any compressed air use, but is especially important in blasting and painting. It can be overcome by special attention to moisture control equipment. The same problem exists in a two stage unit too - just to a lesser extent - and only because the air comes off the compressor at a cooler temperature to begin with.

In summary, two stage units are more likely designed for continuous duty, run slower, last longer, run cooler and run more efficiently regarding power consumption. They are more expensive but are typically a "better" all around unit. Are they needed for most home shop purposes? No.

Rod

Follow Ups:

Re: One Stage vs. Two Stage Compressors Frank Stalfire 19:30:46 03/22/05 (2)
- Re: One Stage vs. Two Stage Compressors CNKS 06:32:20 03/23/05 (1)
  - Re: One Stage vs. Two Stage Compressors Rod (NH) 09:28:00 03/23/05 (0)
Re: One Stage vs. Two Stage Compressors JKC 03:59:40 03/22/05 (0)

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