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Hi Pete, I'll give you my thoughts: I can't say that I have noticed any specific exaggeration of compressor capacity ratings (e.g. XX cfm @ YY psig). There is some confusion with those ratings but no exaggeration as far as I know. It's the HP ratings that seem to be inflated beyond reason. Perhaps that's because the tendency for many is to simply equate more HP with more performance in general. That's not always true. The problem appears to be in the under 10 HP category where there are a mulitude of different maufacturers in rather fierce cost competition for the home-user market. The actual cfm capacity rating is the best way to evaluate what you are getting for your money (quality and longevity not considered). That rating is usually given as so many cfm or scfm at some pressure. It is importrant to recognize exactly the terminology here because all is not consistent among manufacturers. For example, scfm should never be used as a rating since it is dependant on machine location. The same machine at high altitudes will perform significantly different from the same one at sea level. The psig in the rating is the discharge pressure that the compressor is operating at when the cfm is determined. That is usually taken to be at both 90 psig and 40 psig. The 90 psig rating point is the important one because your tank pressure will likely be 90 psig or more for most common pneumatic tasks. The cfm is always the cubic feet per minute of air at the temperature and atmospheric pressure at the inlet of the compressor. For a reciprocating compressor, the cfm rating is a function of the piston displacement, the operating speed and the volumetric efficiency of the machine at the stated discharge pressure. Pneumatic tool ratings are another story and these are necessary to fully evaluate if the compressor can adequately supply any specfic tool or task for a reasonable time. Those ratings can be quite confusing if one is not familiar with the terminology and standard usage. Unfortunately the rating terms are sometimes different (or at least incomplete) between different manufacturers. They are usually also to a different baseline than the compressor ratings are. The area is ripe for claims that are, at a minimum, misleading. And many are, typically resulting in an underrating of the tool relative to its' real air consumption. I don't know if this is due to technical ignorance on the part of the marketing teams or a deliberate attempt to mislead. Perhaps some of both, especially in the home market categories. Certainly, the use of terms like average cfm or cfm without a throttle pressure being stated should be a reason for caution in using any number describing the tool. Disappointment can result when the tool cannot be adequately supplied by the compressor even though the "numbers" would seem to indicate that it could. Again, buyer beware.  Rod
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