Dodgeman, I am definately, positively not an expert in this--but I can sell you a compressor and tell you how to contact an expert, which is all I need to know to sell them. LOL And, no, I am really not trying to sell you one.
But, we have to get beyond the stuff that we learned in Chem/Physics 101. You need that to design, calculate theoreticals, etc., but you start adding in those "real world" factors like heat and friction losses that we ignored then to learn the concepts. In most cases, the manufacturers of compressors show numbers that they can achieve in the real world. If they had an infinate sized tank and an infinate volume sized compressor, all sorts of interesting things are possible, particularly if the air didn't slow down going around corners and things even though the area going the corners. Throw in some Bernoldi factors as the real world areas increase and decrease and the flow rates speed up and slow down with changes because of the real world size of passages (things like a gasket is actually a 1/16" bigger or smaller than the two tubes or passages its sealing and connecting) and hopefully you start seeing why the numbers don't match up. If you had the air pump output volume accurately sized to the open exhaust volume of the tank, you could put the average pressure of the pump out of an open tank outlet forever--at least in the theoretical world. In the real world, parts heat and wear and motors burn up. So the manufacturers show numbers for design calculations so this doesn't happen, at least for a while, and build design safety factors into the product so warrantee costs and production costs don't cause the product price to be totally outrageous. In other words, they just don't let you run the equipment so close to theoretical numbers that it breaks trying to keep up with the theory.
I have a customer that is going to buy a compressor when the rod in his current compressor finally breaks. It has been banging like crazy for 2 years now. We all thought that it would go more than a year ago but it keeps going because the rest of the design factors in the compressor will not let it run at it's theoretical maximum. It will break eventually, but the total design package forces are keeping it going and going and going by not letting the rod work at it's maximum potential. If that makes sense?