SMALL VOLUME AIR COMPRESSOR SIZING for Sandcarver

Questions about how much compressed air will be needed are very important. Large tanks are only as large as the storage capacity above the blasting pressure and or the minimum machine control pressure. Most sandcarving applications use the direct pressure abrasive delivery method operating with blasting pressures 40 psi and lower. Most direct pressure systems operate with pneumatic controls that must maintain a constant 80-90 psi line pressure for proper machine control. Simply stated, the pressure required is normally 80-90 psi even if the actual blasting pressure is lower. Never rely on tank size or capacity to make up for less than required cfm volume.

1. Always look at the compressed air volume supplied at or above any blasting pressure and consider the minimum machine control pressure. If the pump is poor quality, the air volume will be greatly reduced as tank pressure increases. Never accept pump displacement ratings for air supplied. Never simply look at the motor horsepower! You can't fill your tires when the tank read ZERO PSI and the largest motor on the smallest pump has no volume!

2. Make sure you know the duty cycle of any compressor you purchase. Often the pump is operating at a faster speed than normal generating higher than normal frictional piston heat. It is this heat that requires compressor-cooling time, known as Compressor Duty Cycle. This information, "Duty Cycle", is measured in 10 minute time periods. Often duty cycle appears as a percentage of 100.. Duty cycles take into account the amount of time the compressor needs to be off to cool. If the compressor has a 60% duty cycle, it means the compressor must be off for 4 minutes of every 10 for cooling...this is fairly loose but used when warranty is required.

The best duty cycle is 100% and the compressor pump is usually larger and slower in actual compressor RPM's. Don't let lower duty cycles prevent you from purchasing any unit if the other features are positive.

3. Cast iron heads are best...just think about cast iron, heat and durability.

In review the more air volume the better...the best duty cycle is 100%...cast iron is better than aluminum...and the final determining factor is electrical power available. If you only have 220 single phase the best possible air volume you can expect to purchase is about 23-24 cfm at 175 psi remembering that screw compressors and dual pistons heads on a single tank are exceptions.Everything else is a compromise with price being the first contributing factor for final selection.Almost all of the higher air volumes will be TWO-Stage Compressors.

With direct pressure abrasive delivery systems, pressure pots, the blast nozzle is the air orifice-nozzle that determines how much air volume is required. As this type of nozzle wears you must supply more air volume to maintain the desired blasting pressure. It is always advisable to purchase more air than the unit will need to compensate for direct pressure nozzle wear. A 3/32" direct pressure nozzle requires 5.6 cfm volume, (+ or -), to maintain 30-psi blasting pressure. The 1/8" nozzle requires 8.3 cfm volume to maintain 30-psi blasting pressure. All CrystalBlast machines use the industrial pinch valve for machine on-off control. This valve must maintain 80-90 psi line pressure for proper operation. Compressor volumes for all CrystalBlast machines are recommended at 9-10 cfm at 90 psi using the standard 3/32" nozzle.this is not an absolute but a suggested volume.

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