Selecting the properly sized air compressor for an abrasive blasting (aka ‘sandblasting’) application is directly related to the nozzle size and the air pressure being used. A larger nozzle will require more air volume (cfm – cubic feet per minute) as will a higher blasting pressure. The following chart provides some details for the minimum air requirement:
1/8″ (#2) nozzle @ 90 psi – 20 cfm
3/16″ (#3) nozzle @ 90 psi – 40 cfm
1/4″ (#4) nozzle @ 90 psi – 75cfm
5/16″ (#5) nozzle @ 90 psi – 125 cfm
3/8″ (#6) nozzle @ 90 psi – 175 cfm
7/16″ (#7) nozzle @ 90 psi – 240 cfm
1/2″ (#8) nozzle @ 90 psi – 310 cfm
Generally speaking for every 10 psi increase or decrease in air pressure used, a 10% increase in available cfm is recommended. For example, when blasting with a 1/4″ nozzle at 100 psi, 83 cfm is recommended or 68 cfm if blasting at 80 psi.
To determine the horsepower (HP) of the compressor needed to generate the required air volume, a simple rule of thumb is that each HP will generate about 4 cfm of air (i.e., a 25 HP compressor will generate about 100 cfm). If setting the blasting pressure (psi) at the compressor, be sure to factor into the calculation a pressure drop of at least 3 pounds for every 50 feet of air hose or piping (and more if there are tight bends).
Always err on the side of ‘too much’ air. After speaking with blasting contractors for years, the most common refrain is “you can never have too much air”.