Compressor air requirements for abrasive media blasting
Or, “I have plenty of air from my compressor”
One of the most often asked questions we get is how big of a nozzle can I use for my abrasive blasting? The discussion often goes like this:
Customer: What size nozzle should I use?
Abrasives Inc: Before I can recommend a nozzle size I need to get more information from you. Can you tell me the cfm output of your compressor?
Customer: I don’t know, but it’s a good size compressor, it puts out 100psi.
Abrasives Inc: Ok thanks, but psi doesn’t tell me the amount of air it puts out I really need to figure out the cfm. Do you know what the horsepower on it is?
Customer: I think it is 25HP or so, it’s pretty big.
Abrasives Inc: Thanks that helps me get an idea of the cfm output, so a compressor that size puts out approximately 100cfm. Are you also running your blasting respirator off this compressor?
Abrasives Inc: Ok, so based on the information you provided, you can run nothing larger than a #4 ( ¼”) nozzle. I would recommend starting with a #3 (3/16) nozzle, that way as it wears you will still be able to operate efficiently.
Customer: That is the biggest I can use? I was hoping to use a larger nozzle to get the job done faster.
Abrasives Inc: Unfortunately, your compressor just doesn’t have the air available to operate a bigger nozzle efficiently.
The cfm, or volume, of air put out by the compressor is a crucial part of any abrasive blasting operation. It tells us how much air is available to blast with. The higher the cfm, the more air. The more air, the bigger the nozzle one can use. The bigger the nozzle, the more productive the blaster can be.
Whereas psi affects the speed of the air and media. Obviously, psi is important in productivity because the faster one can blast, the more quickly the job gets done. But the cfm of air is still the main variable in that equation. Most compressors of any size can put out 100psi. But a 1600cfm compressor will be much more productive than a 185cfm compressor. Because, you have more air available, you can use a bigger nozzle, giving you a bigger blast pattern.
Not having enough air from the compressor can also cause issues with the operation of the blast pot. If there is not enough air pressure coming from the compressor you can get abnormal wear on your media valve and other parts. Or, the blast pot can turn off unexpectedly, if there is not enough pressure to overcome the spring tension in the inlet/outlet valves.
The section below from the air requirement chart, shows the air requirements for nozzles. In getting back to the discussion above you can see that with only approximately 100cfm of air available from the compressor that they will not be able to use anything larger than a #4 (1/4”) nozzle, and they would not be able to blast at 100psi.
You need to account for all equipment running off the compressor when figuring out how much air is available for the nozzle. At 100psi a #3 (3/16”) will use approximately 45 cfm, the respirator will use approximately 20-25cfm. Any air leaks with fittings and couplings also robs air from the compressor. You also need to keep in mind that as the nozzle wears the orifice is getting bigger and thus, pulling more air. So when deciding on a nozzle it is best to go down at least one size. That way you can get more life from your nozzle.
Please call Abrasives Inc for any questions you have on nozzle recommendations or if you would like to get copies of these or other charts we have available that show the relationship between air cfm, nozzle size, and productivity.
contributed by Mark Mattson, Abrasives Inc. – MN