Compressor Selection
GUIDE TO AIR COMPRESSOR SELECTION
Customer satisfaction with a sandblasting cabinet goes hand in hand with the air compressor and support equipment being used. It is imperative that the air compressor produces enough volume of compressed air (CFM – cubic feet per minute) to operate the blast cabinet per the compressor manufacturers specifications. For the customer, the most critical factor when choosing a compressor should be the volume of air (CFM) that the air compressor generates. The volume of air will be a large factor in determining the productivity of the blast cabinet as it relates to the corresponding blast nozzle.
The following factors should be considered when sizing a compressor:
Duty Cycle: The duty cycle is the percentage of time, in ten minutes increments, that the air compressor pump should be allowed to run. For instance, if the air compressor has a duty cycle of 50%, the air compressor will be running for 10 minutes, then it should run for a combined maximum of 5 minutes ON and 5 minutes OFF TO COOL. As the duty cycle increases the pump can run for longer periods of time without a cooling break. Typically, rotary screw air compressors have longer duty cycles than reciprocating air compressors. Most piston air compressors are available with 100% duty cycles. This high duty cycle is normally a result in a slower compressor speed allowing cooler compressed air production. For more information, refer to our air consumption chart.
Air Volume (CFM): Sand blasting cabinet users commonly size air compressors based on the compressor’s horsepower (HP) rating. The historical rule of thumb states that each compressor horsepower would produce four CFM. Therefore, a 20-horsepower compressor should theoretically produce 80 CFM of compressed air. However this no longer holds true, especially with air compressors that are 10 horsepower or less. Currently, it is not unusual for small 5 horsepower air compressors to produce less than two CFM for every horsepower. Therefore when shopping for an air compressor, pay more attention to the CFM produced than the motor HP.
If a reciprocating piston air compressor (see definition below) is to be used, it is always better to oversize the compressor than undersize it. Determine your current cfm requirements; take into consideration future requirements and airline loss due to compressor location, then multiply the total CFM by 1.5. This will provide enough compressed air for normal operation.
Air Pressure (PSI – pounds per square inch): The pressure is determined by the desired blast pressure in the blast cabinet. It is important that the air compressor maintain air pressures higher than required by the sandblasting cabinet. If the blast operation requires 80 psi, then a single stage compressor (see air compressor definitions) that operates between 95-125 psi will work assuming the compressor produces enough air volume (CFM) to not operate on the tank size.
When considering the purchase of a piston type compressor for smaller sand blasting cabinets, always use the cfm produced at 90 to 100 psi and not the displacement number. Displacement is the mathematical volume produced by one revolution of the pump piston area in cubic inches, times 60 seconds to yield cubic inches per minute. You must then convert this from cubic inches to cubic feet dividing by 1728 cubic inches per cubic foot. The problem is this number is has no air inside the tank and as the tank pressure goes up the air being produced goes down.
Power Source: Oftentimes, the electrical power available to operate the air compressor is the limiting factor. The most common electrical power outlet is rated at 115V (120V) and 20 amps. This limits the size of the air compressor motor to about 2 HP and too small to operate much but a very slow and small pencil blasting machine. Operating a small cabinet air compressor is similar to operating an electric dryer or home air conditioner requiring a higher 208 to 230 single phase power supply.