Compressed Air Glossary: T to Z

Two Stage Compressors: A compressor having two chambers & one air discharge.

Temperature, Discharge: The total temperature at the discharge flange of the com­pressor.

Thermal Compressor: An ejector used to compressor waste or any gas through moderate compression above atmospheric pressure.

Tilting Pad: A type of journal bearing in centrifugal air compressors.

Theoretical Power: The power required to compress a gas isothermally through a specified range of pressures.

Trunk Compressor: A compressor belonging to the group of displacement reciprocating compressors.

Trunnion: A cylindrical projection used as a mounting and/or pivoting point.

Tugger: A device which is operated by air to pull or tug in an effort to move something.

Two Step Control: Load/unload control system which helps maximize the efficiency of compressor by matching air delivery & air demand.

TXV Valve: Thermal Expansion valve.

Ultrasonic Leak Detector: An instrument which helps to detect ultrasonic emissions & alter them to audible signal.

UNC: Unified National Coarse. It is a thread form with rounded roots & flat crests with 60 degree flank angle. As for a given diameter it has larger thread pitch.

UNF: Unified National Fine. It is a thread form with rounded roots & flat crests with 60 degree flank angle. As for a given diameter it has smaller thread pitch.

Unit Type Compressor: A machine in which compressors of 20 HP or less are combined with all the required components to start the operation.

Unloaded Horsepower: The power consumed to overcome the frictional losses while operating in an unloaded condition.

Vacuum Pumps: Compressors that operates by in taking atmospheric pressure & discharging atmospheric pressure or slightly higher.

Valves: A device with passages that helps directing the flow of air into alternate paths.

Vane Compressors: A single shaft positive displacement rotary compressor.

Vapor Pressure: The pressure exerted by the vapour bounded within the given space. The vapour can be a sole occupant or associated with other gases in the space.

V Belt Drive: A drive that transfers power to compressors.

Volute: A spiral shaped stationary passage that converts velocity head to pressure.

Voting Alarm: A 3 sensors alarm system that is connected to compressors or turbines & requires at least 3 alarms before the alarms act.

Water-cooled Compressor: Compressors that are cooled by water circulating jackets surrounding the cylinders or casings.

Whipcheck: Safety cables that help restrain air hoses if any end breaks.

Working Pressure: A normal working pressure required to operate an air motor.

Xenon: An inert gaseous element.

Yoke: A portion of safety valve that surrounds the spring.

Zero: The temperature of pure melting ice under standard atmospheric pressure on the Centigrade & Réaumur scales.

Compressed Air Glossary: M to S

Multicasing Compressor: When two or more compressors, each with a separate casing, are driven by a single motor or turbine, the combined unit is called a multicasing compressor.

Multistage Axial Compressor: A machine having two or more rows of muting vanes operating in series on a single rotor and in a single casing.

Multistage Compressors: Machines employing two or more stages.

Modulating Control: Compressor controls will run the compressor at varying loads to accommodate demand variations.

Off-Load: The compressor which is running & consuming power but is not delivering air.

On-Load: The compressor producing air, either at part load or full load.

Oil-free air: Compressed air produced by a compressor with no oil present in the compression cycle.

Oil Separator: A device that separates oil from the condensate.

OSHA Valve: Valve used to depressurize a system when pressure drop is noticed.

Packaged Air System: Self contained unit consisting of a compressor, a prime mover & various accessories.

Pascal (Pa): The SI derived unit of pressure.

Pressure Drop: A term used to describe the decrease in pressure from one point in a pipe or tube to another.

Pressure Regulator: A device used to decrease the incoming pressure to a lower level & maintains it irrespective to the changes in inlet pressure & outlet flow rate.

Prime Motor: A machine used to derive a compressor.

Particulates: Solid materials such as dust, rust, pollen, etc that is present in air stream.

PPM: Parts Per Million, measurement of the oil present in compressed air.

Receivers: Tanks used to store compressed air & help damp discharge line pulsations.

Reciprocating Compressor: It is a positive displacement compressor which is driven by a piston having a reciprocating motion in a cylinder.

Reduced Pressure: Ratio of actual pressure of a gas to its critical pressure.

Reheaters: Heat exchanger for increasing the temperature of compressed air to increase its volume.

Rotor: A rotating element in a machine & is composed of impeller & shaft.

Rotary Compressor: An air compressor using a rotary impeller driving air through a curved chamber to compress the air.

Regulator: An automatic or manual device designed to control pressure, flow or temperature.

Relief valve: A type of valve used to control or limit the pressure in a system or vessel which can build up by a process upset, instrument or equipment failure.

Refrigeration Dryer: A device consisting of a heat transfer system, a moisture elimination system and a refrigeration system designed to improve the quality of the air and reduce the temperature of the air.

Safety Valve: A device that limits liquids & gas pressure by discharging some of the pressurized liquid or gas.

Safety Relief Valve: An automatic pressure relieving device actuated by the static pressure upstream of the device, which opens in proportion to the increase in pressure over the opening pressure.

Standard Air: Air at a temperature of 68 °F, a pressure of 14.70 psia and a relative humidity of 36 per cent (0.0750 density) (as per A.S.M.E. however in the gas industry the temperature of standard air is usually given as 60 °F.

SCFM: Standard cubic feet per minute.

Set Pressure: The gauge pressure at which a safety valve visibly and audibly opens or at setting which a relief valve discharges an unbroken stream of liquid.

Shaft: A rotating element part on which a rotating division is mounted & therefore helps transmits energy from the prime mover.

Surge Limit: It is the capacity below which the compressor operation becomes unstable.