compressed air treatment

Compressed air treatment glossary


  • Aftercooler: Heat exchanger for cooling air discharged from air compressors; can be either water-cooled or air-cooled.
  • Air/oil separator: A device in the compressor that separates oil from the air/oil mixture compressed in the airend.
  • Breathing air systems: Air purifying systems that produce compressed air meeting OSHA standards for Breathing Quality Compressed Air.
  • Drain traps: Collect and discharge liquids from aftercoolers, separators, receivers, dryers, filters, and drip legs.
  • Dryers: Remove moisture from compressed air.
    • Refrigerated dryers cool air to remove moisture by using a refrigeration cycle.
    • Desiccant dryers reduce dew point by flowing wet air through desiccant beads; heat reactivated desiccant dryers use heat to regenerate the desiccant bed and are more economical at higher cfm ratings than cold regenerative desiccant dryers.
    • Deliquescent dryers reduce dew point through chemical reaction of air with desiccant tablets.
    • Membrane dryers reduce dew point by passing compressed air through a bundle of hollow membrane fibers; water vapor and a portion of the compressed air permeates the membrane walls and vents to atmosphere.
  • Cubic feet of air per minute (cfm): Volume delivery rate of air flow
    • Cubic feet of air per minute, free air (cfm fad): cfm of air delivered to some specific point and converted back to ambient (free air) conditions.  Actual cubic feet per minute (acfm). Flow rate of air measured at some reference point and based on actual conditions at that reference point.
    • Inlet cubic feet per minute (icfm): cfm flowing through the compressor inlet filter or inlet valve under rated conditions.
    • Standard cubic feet per minute (scfm): Flow of free air measured at a reference point and converted to a standard set of reference conditions (e.g., 14.7 psia, 68°F, and 36% relative humidity).

  • Pressure: Force per unit area
    • Pounds per square inch (psi). Force exerted by compressed air equal to 1 pound applied evenly
    • Pounds per square inch absolute (psia). Absolute pressure above zero pressure.
    • Pounds per square inch differential (psid). Pressure difference between two points.
    • Pounds per square inch gauge (psig). Gauge pressure, measured as the difference between absolute pressure (psia) and ambient pressure.
  • Pressure dew point: Temperature at which water will begin to condense out of air at a given pressure. To ensure that no liquid water is present, the pressure dew point must be less than the lowest temperature to which the compressed air will be exposed.

ISO 8573.1 Quality classes

ISO 8573.1 quality classes
ISO 8573.1 was developed in 1991 by ISO (International Organization for Standardization) to help plant engineers specify desired compressed air quality globally by providing “Quality Classes” for solid particulates, humidity and oil. Quality classes provide engineers with an inter-nationally accepted unit of measure. A typical pharmaceutical plant, for example, would have a compressed air specification of ISO Quality Class 1.2.1. This is equivalent to 0.1 micron particulate filtration, -40° F (-40°C) dew point, and 0.008 ppm (0.01 mg/m3) oil filtration.