Air compressor ratings

Ignore HP as others have said, but look at the amp draw to approximate HP or compare one to another. I've seen a lot of 15 amp 5 hp compressors recently but that is just impossible!

You really cannot go much by current hp ratings in the under 10 hp class. There is an awful lot of competition in that market and many manufacturers try to inflate their "ratings" by using a meaningless, non-standard high hp rating. You can only go by cfm rating and you have to be careful there. No compressor can be properly rated in terms of scfm (standard cubic feet per minutre). Compressors are properly rated in terms of inlet cfm, icfm or just plain cfm, which, in this particular case, is interpreted to mean cfm at the pressure and temperature conditions existing at the intake to the machine. This is sometimes referred to as "free air" cfm. When the pressure at the intake is normal atmospheric pressure at sea level and the temperature is 70 deg F, then cfm is the same as scfm.

The atmospheric pressure has a much greater influence on the actual delivery in terms of scfm than the temperature does. For instance, a 15 cfm rated compressor at sea level will have a delivered capacity of 15 scfm. That same compressor, located in Denver, CO., has the same 15 cfm rating (remember, this is volume at the intake conditions - whatever they may be) but has a delivered capacity of about 12 scfm - a 20% reduction caused by the lower atmospheric air pressure at the higher altitude. This is why compressors should never be "rated" in terms of scfm - that rating could change depending on where the compressor was located. Don"t forget also that a dirty intake filter will have the same effect as moving the compressor to a higher altitude - it will reduce the compressor capacity in terms of scfm. The delivered scfm is also slightly dependent on the discharge pressure because of efficiency changes in the compressor as the discharge pressure increases, but that"s another subject altogether.

Rod

IR, Champion, Quincy, C-H, Speedaire, Dayton.

www.tptools.com has very good units, but shipping will eat you up no matter who you buy from if its not local. Look at local deals if you can, so you can haul it home and save the shipping.

Unless the compressor is going to run several hours a day every day, I would not get too hung up on pressure lube, auto drains, super duper this and that, buy a good brand and use it.

I have a Home Depot Husky (a relabeled Campbell-Hausfeld) that is true 7 hp (mexican motor) and 80 gal vert tank and two stage pump (both american made) good unit about 24 cfm but C-H has changed the unit and the near identical looking pump appears to be China made now.

Charles

If you were in industrial compressor sales, this might be true, but given the wild claims for PEAK horsepowers, and with honest RUNNING horespower on consumer compressors, being is half or less of the peak, I tell people to don't bother to try to look at HP, unless you know what the true running hp is. Ignore any peak numbers you see and if they don't tell you "peak" or "running", pass.

Charles