Horsepower, Theoretical, or Ideal: The ideal, or theoretical horsepower of a compressor is defiled as the horsepower required to compress adiabatically the air or gas delivered by the compressor through he specified range of pressures.

Inter-Coolers: These are heat exchangers for removing the heat of compression between stages of a compressor. They usually condense and remove a considerable amount of moisture as well.

Load Factor: This factor is the ratio of the average compressor load during a given period of time to the maximum rated load of the compressor. It applies also to air tools, where it is the product of the work factor times the time factor.

Low Pressure Orifice Test: is a method of accurately measuring the air delivered by the compressor. It is the method recognized by the Compressed Air and Gas Institute and Bureau of standards.

Mechanical Efficiency: is the ratio of the indicated horsepower in the compressing cylinders to the indicated horsepower in the power cylinders, in the case of steam-driven or internal combustion engine-driven compressors, and to the brake horsepower delivered to the shaft in the case of a power driven machine. It is expressed in percent (%).

Moisture Separators: are devices for collecting and removing moisture precipitated from the air and gas during the process of cooling.

Multi-Stage Compressors or Compound Compressors: are those in which compression from initial to final pressure is completed in two or more distinct steps or stages

Normal Air: The term used for average atmospheric air at sea level in a temperate zone where it contains some moisture. It is defined in the ASME Test Code For Displacement Compressors as being at 14.696 PSIA, 68°F, 36% RH, and weighing 0.075 lb/cu ft. The K value is 1.395.

Overall Efficiency: is the product of the compression efficiency and the mechanical efficiency

Portable Compressors: are those consisting of compressor and driver so mounted that they may be readily moved as a unit.

Positive Displacement: A machine where successive volumes of air or gas are confined within a closed space and pressure is increased as the volume of the closed space is decreased.

Pressure (PSI): Pounds-Per-Square-Inch: A rating of Air Pressure in the system.

(PSIG) "Gauge": Gauge pressure shows amount of air pressure above ambient

Pressure Discharge: Discharge pressure is the absolute total pressure at the discharge flange of a compressor.

Pressure, Intake: Intake pressure is the absolute total pressure at the inlet flange of a compressor.

Pressure Rise: This is the difference between the discharge pressure and the intake pressure.

Pressure Static: Static pressure is the pressure measured in a flowing stream (liquid or gas) in such a manner that no effect on the measurement is produced by the velocity of the stream.