Two stage air compressor

A 2 stage compressor is MORE efficient because the air is cooled between stages. Mechanical energy is not wasted as heat as it is in a single stage. As for the higher CFM ratings, there is really no such thing as a 6hp compressor. There is a lot of lying going on in this segment of the market. Get the data off of the motor. 1hp = 750 watts. Watts= volts x amps. I bet it doesn't add up to 6hp. Probably more like 3.5 or so. A rule of thumb, a reputable compressor maker will NEVER claim more than 4cfm per electric motor horsepower. That is a simple fact of physics. I bet the more expensive compressor is simply claiming its output closer to reality than the old one. Beware. Even quality companies like Quincy and IR are being forced to build overstressed units to compete with the junk on the market. One 5hp IR I saw recently was turning 1450 rpm, and it was a good cast iron unit, but a 3hp turning to produce 5hp worth of air. It is almost impossible to turn a true 5hp motor on a household electrical service. Finally, disregard all cfm ratings below 90-100 psi. Who cares how much cfm you get at 40 psi, what do you run at such a low pressure?

The two stage is more efficient because it compresses the same air twice. Its not just two cylinders pumping air, its compressed in one cylinder then pumped to the second cylinder and compressed further before it goes into the tank.

Don't discount the little fact you threw in about it running slower. Thats a big factor in how long the thing's gonna last. You can just imagine an aluminum cylinder turning 2 or 3 thousand rpm, as compared to a cast iron cylinder running at 6 or 8 hundred rpm. The slower unit will last years longer.

Good luck.

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