Inadequate air Pressure
When the sandblaster drops below a functional level, the operator will notice the gun is shooting out mostly air with little abrasive material. Check the pressure gauge at the regulator and the compressor. You probably have insufficient air pressure to operate the gun. Remember that siphon guns require more air than pressure pots.
Moisture
If the pressure is OK but only air is coming out of the gun, then the abrasive line is likely plugged or leaking. Sandblasters need very dry, abrasive material or they tend to clog up. When clogged, the sandblaster will generally work only in bursts until the abrasive material is used up. Siphon sandblasters are more sensitive to moisture problems than pressure pots.
Nozzles
If everything else seems normal but the effect of the abrasive is diminished, check your nozzle. Worn nozzles will cause the spray pattern to enlarge and decrease the effectiveness of the sandblaster. If you have this problem, consider upgrading to a Tungsten carbide or Boron carbide nozzle. They are higher priced but provide many more hours of use and withstand a much higher airflow and more punishing abrasives.
Dust Accumulating
Sandblasters create dust. A well-designed sandblaster will have a vacuum system attached to the side of the cabinet. If the inside of the sandblaster cabinet fills with dust to where it affects your visibility, the problem is probably a non-performing vacuum system. The culprit is usually a filter that needs to be changed or a clogged up vacuum line. A large air leak in the cabinet can cause the same problem but would probably be noticed earlier.
Preventive Maintenance
Preventive maintenance is important if you want to maintain a high-performance sandblasting system. Starting with your air compressor, change the air filters as required; add oil when needed (if oil lubricated); drain the tank at least weekly in humid conditions; and clean and drain air-line water traps. For your blaster gun and cabinet, regularly check for leaks, inspect the nozzle for wear and inspect all feed lines for cracks and wear. Make sure your vacuum system has clean filters. Last, but probably most important, is to make sure you have adequate respirators for operators.