Air Compressor Size, Power and CFM Explained

Having compressed air available in your garage, shed, or business really expands the arsenal of tools you have at your disposal. Air compressors reduce the bodily strain from using hand tools and helps projects get done faster than with electrical tools. From carpentry to auto repair to painting and much more there simply is no substitute for a supply of quality compressed air.

When buying an air compressor, it’s important to select a model that will provide the capacity for your needs. All the efficiency of using compressed air instead of hand labor is lost when you have to repeatedly wait for the canister to fill back up with its supply. Therefore size, power, and cubic feet/minute (CFM) must be evaluated before making an air compressor purchase.

Air Compressor Size

The one surefire way to keep work moving when dealing with compressed air would obviously be to buy the biggest tank available. The truth is you could be generating a lot of wasted compressed air and actually lowering your efficiency when purchasing a compressor with a large tank. Compressor tank sizes range from 1 gallon to 120 gallons. Buying a compressor where the tank is too large takes up work space, becomes less portable, and is overall unnecessary. A compressor too small in size won’t provide the amount of air needed to work efficiently.

Something else to consider in regards to small air compressor size is the two different styles of units – portable and stationary. In commercial settings such as an auto repair shop 80-120 gallon tanks are the norm as pneumatic tools are being operated by multiple users on an almost constant basis. Carpentry contractors generally employ a 4-6 gallon twin stack compressor because it is portable (approximately 50 pounds) while featuring enough air supply to operate nailers, staplers, sanders, and more. Home hobbyists or those who need air only on an emergency basis (car tires) can get by with a 1 pound unit while an industry such as a cabinet manufacturer uses a 40 to 60 gallon tank, either portable or stationary. Essentially, there is a compressor size suitable for almost every use.

Air Compressor Power

The size of the air compressor is basically how much air storage it has. The power of the model refers to the engine size however. Power is recognized in HP, or horsepower. Some people feel that horsepower is an overrated aspect of air compressor power. The reason that people feel this way is because tank size and air delivery (PSI, CFM) are the key factors which dictate the performance of the compressor. Also, compressor manufacturers sometimes rate their products on peak horsepower while others do so at normal operating conditions, adding some confusion for consumers.

Something else to consider about air compressor power is the terms ‘Duty Cycle’ and ‘Service Factor’. The duty cycle is essentially the time that the compressor is operating, some of which are intermittent and others continuous. This is a rating that determines whether the compressor can operate at full horsepower on a steady basis or in short bursts. The service factor is a percentage of the rated horsepower that the compressor can safely operate which amounts to either more or less of the designation (5HP, 10HP, etc.).

Air Compressor CFM

The reason why air compressor horsepower ratings are somewhat underrated is because the real performance comes from the pounds per square inch (PSI) and cubic feet per minute (CFM). Cubic feet per minute determines how fast the compressed air is delivered while the pounds per square inch is a number dictating the pressure at which the air is dispersed. It’s said that CFM ratings are the true indicator of power. If the tank is large enough to store the compressed air needed, than the CFM ratings must deliver that supply at a fast rate depending on what certain tools need. Since different tools are used at various rates, an average CFM is given to them (based on 90 PSI):

Angle disc grinder 5-8 CFM

Cut-off tools 4-10 CFM

Framing nailer 2.2 CFM

3/8” Impact wrench 3 CFM

Mini die grinder 4-6 CFM

Orbital sander 6-9 CFM

Rotational sander 8-12.5 CFM

Brad nailer 0.3 CFM

Drill 3-6 CFM

Grease gun 4CFM

1/2” Impact 4-5 CFM

Needle scaler 8-16

1/4” Ratchet 3 CFM

Shears 8-16 CFM

Chisel/Hammer 3-11 CFM

Dual Sander 11-13 CFM

Hydraulic riveter 4 CFM

1” Impact 10 CFM

Nibbler 4 CFM

3/8” Ratchet 5 CFM

Speed saw 5 CFM

If you know which type of tools you normally use, it can help determine the CFM capabilities that are needed in a compressor.

Some other factors which lead to an air compressors power include whether it is a single stage or dual stage electric design. In a dual stage compressor the air is compressed twice, allowing it to reach pressure of 175 PSI compared to 125 PSI in a single stage. The higher pressure allows for increased storage in the tank. Gas powered units also may provide more power over electrical compressors because they aren’t limited by 120V or 240V outlet limitations.

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