CFM:  Cubic Feet per Minute is the measurement of airflow that indicates how many cubic feet of air pass by a stationary point in one minute.

CFM Displacement:  This is the measure of the cylinder displacement multiplied by the pump RPM.

SCFM:  Standard Cubic Feet per Minute is the CFM measure based on standardized air temperature, pressure, and humidity.  A pump’s SCFM will always be less than CFM Displacement because no pump is 100% efficient.

PSI:  Pounds per square inch is the pressure resulting from a force being applied to every inch of an object.

Single stage:  Air is compressed to final pressure in a single stroke.  Single stage compressors are most effective when compressing air to 100psi or less.  Single stage units may have one or more equally sized cylinders.

Two stage:  This type of compressor uses cylinders of unequal bore size to compress air in two stages.  The first stage of compression is produced in a large cylinder to compress the air to 50-70psi.  The air then passes through an intercooler to a smaller cylinder where it is compressed again to 175-200psi.  Two stage compressors are the most efficient way to achieve pressures over 100 psi.

Heat:  As air is compressed, it heats up.  Because hot air naturally wants to expand, cooling the air with intercoolers and aftercoolers makes the pump’s job easier, and improves efficiency.

Intercooler:  A finned tube used to reduce the temperature of the compressed air between stages of compression.

Aftercooler:  A mechanism used to reduce the temperature of the compressed air after the final stage of compression.  Some pumps have small aftercoolers.  An aftercooler component can also be added after the tank.

Moisture:  To achieve 120psi, 8 cubic feet of air is compressed into 1 cubic foot.  Air can be compressed, but the water in the air (humidity) does not compress.  The relative humidity reaches 100% and as the compressed air temperature drops, condensation forms water in the tank. 

Air Dryer:  A system used to reduce or eliminate excessive moisture in the compressed air. Reducing moisture can extend the life of tools, and in some cases, such as environments where freezing may occur, a dryer is necessary. 

Separators:  Accessories plumbed into the air system to collect and remove moisture, dirt, oil and any other contaminates from the air system.