Some blasters think that a moisture separator in place of an air prep unit is adequate but it must be noted that a moisture separator only removes the incoming heavy moisture. Some consider an after-cooled compressor to have the same effect as an air prep unit. But inbuilt aftercooled compressors can lower pressure by 12-14psi (18-21% efficiency loss). Air prep units on the other hand have only a 3psi drop. Visit : https://quantumblast.com.au/the-importance-of-an-air-prep-unit-in-dry-sandblasting/ for more information .