You need to have a water trap/filter right at the sand blast hopper and you need 90 psi at the blaster.
You also need DRY SAND, if it's been laying around in a humid area it will not flow smoothly.
Poor quality sand with larger grit sizes will also give you a fit if it's to big for the tip size you're using.
Are you adjusting the mixing valve to get the correct flow?
Mike B
