This page lists compressors rated roughly 38 to 42 CFM. At this output the catalog shifts from piston to rotary screw: a 10 HP fixed speed screw such as the Chicago Pneumatic QRS 10, a 7.5 to 10 HP variable speed screw such as the Atlas Copco GA5 VSDS or G7L, or a 15 HP ABAC Ironman duplex piston set for shops that want two pumps and a big tank instead of a screw.

Why rotary screw takes over at 40 CFM

A rotary screw delivers about 4 CFM per horsepower at 125 PSI and is rated for 100 percent duty, so a 10 HP screw makes the same air as a 15 HP two stage piston that has to rest between cycles. It also runs 10 to 15 dB quieter and delivers cooler air. The trade is price, a required annual service kit, and the need for a separate receiver tank on base mounted models. Variable speed drive pays off when demand swings through the day; a fixed speed screw is the better buy when the load is steady.

What 40 CFM supports

Ten to twelve service bays, a body shop with two painters, a sign or millwork shop, a tire and alignment center, or a light manufacturing cell with CNC air blast and blow off. Plan on three phase power, 208 to 460 volt, and a 40 amp circuit for the 10 HP screws.

Dryer sizing

Use a 50 CFM refrigerated dryer. Several rotary screw packages here are offered with the dryer integrated on the tank, which saves piping and floor space. Add a coalescing filter after the dryer for paint or plasma work.

Related pages

• 35 CFM air compressors
• 45 CFM air compressors
• Rotary screw air compressors
• Shop all sizes by CFM