Collection: Piston Air Compressors

A two stage piston compressor makes 175 PSI. A single stage stops around 135 to 155. That one number decides most of these purchases. The second number is CFM, and a good two stage cast iron pump puts out roughly 3.5 to 4 CFM per horsepower at 175 PSI.

Already know your motor size? Go straight to piston air compressors under 5 HP, 5 to 7.5 HP piston air compressors or 10 HP and above piston air compressors.

Single stage or two stage

Single stage compresses in one stroke. Fine for a home garage, a cabinet shop, tire work, a nailer and the occasional impact wrench. Two stage compresses twice with an intercooler between the cylinders, so it runs cooler and holds CFM up at pressure instead of falling off. The crankshaft and cylinder mechanics are here if you want them. If the compressor runs more than an hour or two a day, buy two stage and stop thinking about it.

Where a piston stops

Duty cycle. Industrial two stage pistons are built for about 60 to 75 percent run time in an hour, and the rest is cooldown. If one tool runs continuously and eats more than roughly 60 percent of the pump's rated CFM, you're past what a piston does well and you want a rotary screw. A 6 inch random orbital sander pulls 12 to 18 CFM and doesn't stop. One of those on a 5 HP machine works. Two does not, and we'd rather say so up front than rebuild the pump for you in two years.

The other trap is 120V. A compressor on a 15 amp household circuit is capped near 2 HP of real output whatever the carton claims. Anything above that wants 230V or three phase. And size by CFM at your working pressure, not by tank gallons: the receiver tank buys seconds, the pump does the work.

Comparing specs in bar, litres per minute or kilowatts? The unit converter puts them in psi, CFM and HP, and the pump-up test calculator will tell you whether your current machine is worn or just undersized.