I have found that the cheap siphon feed blasters are not as effected by moisture in the line because the compressed air does not go through the sand. In the pressure pot sandblasters the compressed air is routed through the pressure pot. Therefore, any moisture that condenses will end up in the sand itself causing it to cake in the pot. The sand will not come out or will jam up in the hose. It is absolutely imperative that the air is dry with a pressure pot or you will end up spending your time cussing the thing instead of getting any work done.