Compressed Air Glossary - G thru L

Valuable information for people who work with compressed air systems.

Here's the third addition to the Compressed Air Glossary:

Gas - One of the three basic phases of matter. While air is a gas, in pneumatics the term gas normally is applied to gases other than air.

Gas bearings - Load carrying machine elements permitting some degree of motion in which the lubricant is air or some other gas.

Gauge Pressure - The pressure determined by most instruments and gauges, usually expressed in psig. Barometric pressure must be considered to obtain true or absolute pressure.

Guide vane - A stationary element that may be adjustable and which directs the flowing medium approaching the inlet of an impeller.

Head, Adiabatic - The energy, in foot pounds, required to compress adiabatically to deliver one pound of a given gas from one pressure level to another.

Head, Polytropic - The energy, in foot pounds, required to compress polytropically to deliver one pound of a given gas from one pressure level to another.

Horsepower, Brake - Horsepower delivered to the output shaft of a motor or engine, or the horsepower required at the compressor shaft to perform work.

Horsepower, Indicated - The horsepower calculated from compressor indicator diagrams. The term applies only to displacement type compressors.

Horsepower, Theoretical or Ideal - The horsepower required to isothermally compress the air or gas delivered by the compressor at specified conditions.

Humidity, Relative - The relative humidity of a gas (or air) vapor mixture is the ratio of the partial pressure of the vapor to the vapor saturation pressure at the dry bulb temperature of the mixture.

Humidity, Specific - The weight of water vapor in an air vapor mixture per pound of dry air.

Hysteresis - The time lag in responding to a demand for air from a pressure regulator.

Impeller - The part of the rotating element of a dynamic compressor which imparts energy to the flowing medium by means of centrifugal force. It consists of a number of blades which rotate with the shaft.

Indicated Power - Power as calculated from compressor-indicator diagrams.

Indicator card - A pressure - volume diagram for a compressor or engine cylinder, produced by direct measurement by a device called an indicator.

Inducer - A curved inlet section of an impeller.

Inlet Pressure - The actual pressure at the inlet flange of the compressor.

Intercooling - The removal of heat from air or gas between compressor stages.

Intercooling, degree of - The difference in air or gas temperatures between the inlet of the compressor and the outlet of the intercooler.

Intercooling, perfect - When the temperature of the air or gas leaving the intercooler is equal to the temperature of the air or gas entering the inlet of the compressor.

Isentropic compression - See Compression, Isentropic.

Isothermal compression - See Compression, Isothermal.

Leak - An unintended loss of compressed air to ambient conditions.

Liquid piston compressor - A compressor in which a vaned rotor revolves in an elliptical stator, with the spaces between the rotor and stator sealed by a ring of liquid rotating with the impeller.

Load Factor - Ratio of average compressor load to the maximum rated compressor load over a given period of time.

Load Time - Time period from when a compressor loads until it unloads.

Load/Unload Control - Control method that allows the compressor to run at full-load or at no load while the driver remains at a constant speed.