Four Times is Twice as Big

Just one more quick comment on CFM, nozzle size and blasting...

I discussed a little about the differences and relationship between CFM and PSI in a previous post. PSI is basically the amount of force you blast with. CFM is the volume of air being used during blasting.

It is sometimes suprising to realize how much air (CFM) is required during blasting. At a given PSI setting, the amount of air needed is directly related to the nozzle size being used. The larger the nozzle, the more air that is required. This also means that if you want to use a large nozzle, you will need a large compressor.

For example, at 80 psi, a 1/8" nozzle will require 20 CFM. At the same pressure a 1/4" nozzle will require 85 CFM and a 1/2" nozzle will demand 340 CFM. A basic chart that shows the air requirements for different nozzles at different pressures is on the PPB Series page.

Rule of thumb: double the nozzle size, quadruple the CFM required.

Blasting - CFM vs PSI

There are a few variables that need to be addressed when determining the blasting system that will work best for your application. Two critical issues are the blasting pressure (PSI) and the air requirement (CFM).

PSI {pounds per square inch} indicates the force that the blasting media is being discharged from the nozzle. The PSI measurement is independent of the nozzle size being used and is directly related to the pressure setting on the air compressor and/or the blasting pot. The most common abrasive blasting pressure used is 80 psi.

CFM {cubic feet per minute} is the volume (cubic feet) of air that is being sent threw an opening per unit time (the minute part). The CFM required during blasting is based mostly on the nozzle size being used. A larger nozzle will require more air just like a larger hose will need more water. Abrasive blasting is using air continuously so the compressor used must be able to supply enough CFM to 'keep up with' the blaster. For comparison, pneumatic (air powered) tools only use air in small increments so much less CFM is required.

Side note: For a given nozzle size, the CFM requirement will go down with lower blasting pressures (PSI). Using the garden hose comparison, more water will come out of the hose if the spigot is turned to a higher pressure, less if the spigot is turned down.