Industrial & Commercial Power, Pumping & HVAC Solutions

Compressed Air Basics and Glossary Terms


Ambient Air — the air surrounding you.

Aftercoolers — heat exchanger that cools discharged air from the compressor (provides the most effective means of removing moisture from compressed air; approximately 70% of water is removed).

Air-Cooled Compressors — atmospheric air is circulated around to cool the unit and /or the compressed air.

Air End — compression chamber where air is compressed.

Approach Temperature — temperature above ambient.

Boosters — increase air pressure (usually four times inlet PSI).

Boss Hose Fitting — threaded fitting to connect hose from compressor or extend the length of hose used to flow gases.

Chicago Fitting — (crows foot) 1/4 turn fitting that can connect hose to the compressor or extend the length of hose used to flow gases.

CFM — cubic feet per minute.

Centrifugal Compressors — compression of air/gas through turning impellers.

Condensate — liquid discharged from compressor and/or air treatment equipment.

Dew Point — temperature that moisture changes from vapor to liquid.

Dew Point Suppression — temperature below ambient.

Dynamic-Type Compressors — air or gas is compressed by rotating vanes or impellers.

Filters — devices that separate and/or remove undesired liquids and particulates from compressed air.

High-Pressure Air — compressed air above 150 PSI.

Instrument-Quality (IQ) Air — treated compressed air from an oil-flooded compressor (after-cooled, filtered).

Low-Pressure Air — compressed air 150 PSI or lower.

Multicasting Compressors — one motor can run two or more compression chambers.

Multistage Compressor — compressor with two or more stages.

Microns — measurement used to define particulates in the air stream (one micron equals one millionth of a meter, about one-eighth the thickness of one human hair).

Oil-Flooded Air — compressed air produced by a lubricated air end.

Oil-Free Air (Dry Screw) — compressed air produced by a dry air end.

Oil Separator — device used in an oil-flooded system to recycle oil back to the air end.

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

PSI — pounds per square inch, unit for pressure of compressed air.

Particulates — any solid material, such as dirt, rust, weld fines, pollen, etc., in the air stream.

PPM — parts per million, measurement of the oil present in compressed air.

Receivers — tanks used to store compressed air and help dampen discharge line pulsations.

Reciprocating Compressor — a piston in a cylinder producing compression.

SCFM — standard cubic feet per minute.

Standard Air — air at a temperature of 68°F, 14.70 psi atmospheric pressure and relative humidity of 36% (per ASME). In the gas industry, temperature is 60°F.

Standard Compressed Air — untreated compressed air from an oil-flooded system (not after-cooled or filtered).

Rotary Compressors — compression is produced by the positive action of rotating elements.

Two-Stage Compressors — two-compression chambers (initial to intermediate) with one air discharge.

Whipcheck — safety cable used to restrain air hoses if an end breaks.

Rules of Thumb

1. For every 20° that compressed air drops in temperature, half of the water vapor will change to liquid.

2. A 1,000 CFM air compressor can produce 55 gallons of water in 24 hours of straight run time.

3. 1,800 CFM at 100 PSI is approximately the maximum amount of air that can pass through a 3-inch hose.

4. For electric air compressors, multiplying the horsepower times four will give you the approximate CFM.

5. As the pressure increases, the CFM decreases. Conversely, as the pressure decreases, the CFM increases.

6. All electric air compressors have built-in aftercoolers.

Questions to Ask

1. What are the CFM and PSI requirements?

2. What type of compressor is needed?

  • Diesel (standard, I-Q or oil-free)
  • Electric
  • High Pressure

3. What quality of air is required?

  • Particulates (what micron?)
  • Moisture (dew point)
  • Oil content (PPM)

4. What is the application?

5. What type and size air connections will we pipe to?

  • Pipe thread
  • Flange
  • Boss
  • Chicago (crows feet), etc.

6. What type and size connections do we need on the compressor? (match hose fittings with compressors)

  • Mpt, fpt
  • Boss
  • Chicago (crows feet)
  • Flange, etc.

7. What is the distance from the compressor to the process connection? (How many hose lengths and whipchecks will be needed?)

8. Do you need low ambient (below 35°F) protection?

9. How much room do you have to place the equipment? (Compare to the overall dimensions of the selected equipment.)

10. Is after treatment (after-cooler separators, dryers or filters) needed?

Air Types

Standard Compressed Air (Oil-Flooded)

  • Hot (Heat of compression is approximately 110°F over ambient)
  • Wet (Humidity in ambient air is sent downstream)
  • Oily (Oil-flooded compressors will pass oil downstream)

Instrument-Quality (IQ) Compressed Air

  • Oil-flooded air with after-treatment
  • After-cooled (15–25° of ambient)
  • Filtered (.01 micron and .01 PPM remaining oil content)
  • Cleanest compressed air available

Oil-Free Compressed Air (Dry Screw)

  • No oil utilized in the compression cycle
  • After-cooled (25° of ambient)
  • Minimal filtration (filtered to 25 )
  • Not cost effective and not needed for compressing air

Air Treatment Packages

Aftercooler/Separators (air or electric driven)

  • Reduce compressed air temperature (10-20° approach)
  • Remove 70% of the water
  • 450 to 3,500 CFM capacity (high pressure available)

Aftercooler/Filter Packages (air driven)

  • Reduce compressed air temperature (10-15° approach)
  • Remove 80% of the water
  • Filter particulates to .01 micro
  • Remaining oil content = .01 PPM
  • 450 to 1,600 CFM capacity (high pressure available)
  • Makes a standard air compressor an IQ compressor

Membrane Dryer/Aftercoolers (air driven)

  • Reduce compressed air temperature (10° approach)
  • Reduce dew point to 60° suppression
  • Filter particulates to .01 micron
  • Remaining oil content = .01 PPM
  • 185 to 500 CFM capacity

Refrigerated Dryer Packages (230/460V 3-phase electric)

  • Remove moisture content to 38° dew point
  • Max inlet temperature 120°F
  • 150 to 20,000 CFM capacity

Desiccant Dryer Packages (115V)

  • Remove moisture content -40° or -100° dew point
  • Filter particulates to .01 micron
  • Remaining oil content = .01 PPM
  • Max inlet temperature 120°F
  • 45 to 5,400 CFM capacity (high pressure available)

Aftercooler/Dryer/Filter Packages (115V or 12/24V DC)

  • Remove moisture content -40° or -100° point
  • Filter particulates to .01 micron
  • Remaining oil content .01 PPM
  • 260 to 1,550 CFM capacity (high pressure available)
  • Connect to a standard air compressor

Custom Filter Packages: Per customer request (ISO)

  • Particulate removal (micron)
  • Oil removal (PPM), Oil vapor removal (PPM)
  • Separator/filters, Air line filters
  • Combinations of any of the above filters
  • Max temperature 120°F
  • High pressure available
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