Receivers: Receivers are tanks used for the storage of air discharged from compressors. They serve also to damp discharge line pulsation's.

Reciprocating Compressors: are those in which each compressing element consists of a piston moving back and forth in a cylinder.

SCFM: Standard Cubic Feet Per Minute. At "standard conditions" (see above) will one standard cubic foot of air actually occupy one cubic foot of volume. Another way to express one standard cubic foot of air is .075 of a pound of air. A standard cubic foot varies in volume as it deviates from standard conditions, but it always weighs .075 of a pound. Therefore, SCFM is a measure of weight, regardless of volume. (see corrections for altitude chart)

Seals: Seals are devices used between rotating and stationary parts to separate, and minimize leakage between, areas of unequal pressures.

Single-Acting Compressors: Machines in which compression takes place on one stroke per revolution in each compressing element.

Single-Stage Compressors: Machines in which compression from initial to final pressure is complete in a single step or stage.

Two-Stage Compressors: These are machines in which air or gas is compressed from initial pressure to an intermediate pressure in one or more cylinders or casing.

Vacuum Pumps: Machines for compressing air or other gases from an initial pressure that is below atmospheric pressure to a final pressuring that is near atmospheric

Volumetric Efficiency: The ratio of the actual inlet capacity (ACFM) to the first stage displacement expressed as a percentage. Volumetric efficiency varies by clearance or blow-by, heating losses, valve losses, and specific gravity of gas being compressed.

Water-Cooled Compressors: These are machines cooled by water circulated through jackets surrounding the cylinders or casings.