Before you can choose a nozzle you need to know a bit about the compressor that is supplying it with air. If we had a pound every time someone told us they had a big compressor we'd have retired early. The physical size of a compressor may not bear any relation to the size of nozzle that can be used with it. However if you, like most people, don't actually know the Cubic Feet per Minute (CFM) rating of your compressor then there is a rough rule of thumb that will help you determine what the CFM is. For a piston compressor multipy the horse power by 3, for a vane compressor multiply the horse power by 4.

Considering that a nozzle is just a little hole in a tube at the end of a pipe that the grit comes out of, it is surprising just how complicated it can be to make sure you have the right little hole in the right little tube! So what do you need to think about when you buy a nozzle?

Obvious things first - what are you going to use the nozzle for? If it is for lettering then you need as large a nozzle as possible, bearing in mind that you need a reasonable blasting pressure and making sure that you have some in-built allowance for wear. For designs you will need more control so a fine nozzle is the order of the day. For cleaning a wide spread of grit is the prime requirement; blasting pressure isn’t a high priority.

In an ideal world it follows that if you buy a nozzle initially for designs you can use it for lettering when you start to lose a bit of control and for cleaning when you start to lose pressure. However, as we all know, we don’t live in an ideal world so how do you size a nozzle for lettering?

The first thing you need to know is how much air does your compressor deliver, commonly known as free air delivery. The second factor is blasting pressure – what pressure do you want to blast at? Once you know these two things you can use the table below to work out what size of nozzle you should use. Don’t forget though that as your nozzle wears, so the volume of air it requires will increase – and as the table shows this increase is exponential ie. if the diameter of the hole doubles the volume of air required quadruples.

Nozzle Size Blasting Pressure
40 50 60 70 80 90 100
2.5 mm 6 7 9 10 11 12 13
3.1 mm 10 11 13 15 17 18 20
4.0 mm 17 20 23 26 30 33 36
6.0 mm 40 46 53 60 68 74 81


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