[DanielC]

You need to keep the blasting media dry or it clumps up, and will not flow.
If the sand feed is suction only, if you block the nozzle of the gun, it blows air backwards through the sand feed hose, and removes the clog, but if the sand has moisture, it quickly clog again.
Sometimes suction feed needs a little adjustment on the amount of sand being fed in to the feed hose. You need air to flow in to the hose, to bring sand with it. Kind of like a carburetor, not too rich, or too lean.

You need to vent the cabinet. The gloves should inflate a little, but not go out fully stiff. You need some air flow through the cabinet, to clear the air, so you can see what is blasted, and areas missed. but too much air flow will suck good blasting media out of the cabinet.

Probably should wear a dust mask, to reduce the amount of dust you inhale.