Compressed Air Systems 101



What is Compressed Air?

Air at greater than atmospheric pressure- usually 100 pounds over atmospheric pressure- or 100 PSIG. P.S.I.G means pounds per square inch gauge. Air that has been compressed above atmospheric pressure will return to atmospheric pressure when released. Therefore; compressed air is STORED ENERGY! The amount of this stored energy or the ability of the compressor to supply this energy is expressed in both CFM and PSIG.

CFM or Cubic Feet Per Minute is the volume of air measuring the capabilities of the compressor. A good rule of thumb is one HP will provide about 4 cubic feet of compressed air at 100 PSIG.

Example: 5 HP Compressor will supply 20 CFM at 100 PSIG
100 HP Compressor will supply 400 CFM at 100 PSIG


How to Select a Compressor

  1. Determine the type of compressor needed based on your PSI needs
  2. Determine air consumption: List all equipment and tool requirements, both continuous and intermittent air
  3. Add together the cfm requirements of all the equipment/tools you plan to run at the same time. Increase this number by 20% to allow for additional tools, future growth and eventual air leaks. Determine the maximum pressure (PSIG) needed to run the equipment. Simply use the value of the equipment that requires the greatest amount of pressure. If above total = less than 100 CFM divide this total by four to find HP. If the total is over 100 CFM divide by five.
    1. Example: System requires 310 CFM at 100 PSIG
      310/5 = 62 HP
    2. 60 HP or 75 HP Compressor is needed

Typical Uses of Compressed Air Systems

It is as important as water, electricity and fuel (gas, oil, etc.). The great advantage of compressed air is the high ratio of power to weight or power to volume. In comparing electric motors, compressed air procedures smooth translation with much more uniform force. Compressed air equipment can be more economical and more durable.

Compressed air tools can be operated without the shock hazard of electricity or the explosion hazard of oil.

Industrial Uses of Compressed Air:

  • Production Line Tools
  • Automation & Assembly Stations
  • Plant Maintenance
  • Chemical Manufacturing
  • Aircraft Manufacturing
  • Automobiles-Beverages
  • Agriculture
  • Cement- Foundries
  • Plastics- Construction
  • Hospitals
  • Monuments
  • Power Plants
  • Sewage Plants
  • Painting & Ski Areas
  • Auto/Tire
  • Dry Cleaning
  • Energy
  • Natural Gas
  • Pharmaceutical
  • Woodworking, Etc.

What is the difference between single-stage and two-stage compressors?

Both single-stage and two-stage compressors draw in and compress air. The difference is that two-stage compressors condense/cool the compressed air and then compress it a second time.


How to Select the Right Compressed Air Dryer

  • Know the Specific Uses of the Compressed Air – The selection of an air dryer is done best by the professional who knows or learns the particular end uses, the amount of moisture which each use can tolerate and the amount of moisture that needs to be removed to achieve this level. Air, which may be considered dry for one application, may not be dry enough for another.
  • Know the Temperatures – To determine whether or not the compressed air will remain sufficiently dry, we must know the end use of the air and the temperature at which it must work. In an industrial plant where the ambient temperature is in the range of 70ᵒF or higher, a dryer capable of delivering a pressure dew point 20ᵒF lower than ambient, or 50ᵒF, may be quite satisfactory. A dryer which may be satisfactory for high daytime temperatures, may not be satisfactory for lower nighttime temperatures. In areas where freezing temperatures are encountered, a lower pressure dew point may be required. In general, the dew point should be specified 20ᵒF lower than the lowest ambient temperature encountered in order to avoid potential condensation and freezing.
  • Know the Actual Performance– While many dryers have a standard rating of 100ᵒF saturated inlet air temperature and 100 PSIG operating pressure, it is important to check on the actual performance of the units obtained in actual plant operating conditions.
  • Know Each Use – There are many other uses requiring moisture removal to a low dew point. For example, railroad tank cars, which carry liquid chlorine, are padded (charged) with compressed air to enable pneumatic unloading. Chlorine will combine with water vapor to form hydrochloric acid; therefore, the compressed air must have minimum moisture content to prevent severe corrosion. Droplets of moisture in wind tunnel air at high- testing velocities may have the effect of machine-gun bullets, tearing up the test models. Air used for low-temperature processing (for example, liquefaction of nitrogen or oxygen) can form ice on cooling coils, thus requiring defrosting. The lower the moisture content of the air, the longer the periods between defrosting shutdowns.
  • For these and similar temperature applications, compressed air must not only be free of liquid-phase water but must also have a minimum content of vapor phase water. Usually specified for these requirements are dew points in the range of -40ᵒF to -100ᵒF at pressure.

Why Do Compressed Air Systems Need Drying?

Moisture is Damaging

Moisture in compressed air used in a manufacturing plant causes problems in the operation of pneumatic systems, solenoid valves and air motors and can adversely affect the process or product being manufactured. For many years, problems from moisture in compressed air lines were simply tolerated as unavoidable. Moisture:

  • Causes rust and increased wear of moving parts in production equipment as it washes away lubrication
  • Can adversely affect the color, adherence, and finish of paint applied by compressed air
  • Can jeopardize process industries where many operations are dependent upon the proper functioning of pneumatic controls. The malfunctioning of these controls due to rust, scale, and clogged orifices can result in damage to product or in costly shutdowns
  • Can freeze in control lines in cold weather, which may cause faulty operation of controls
  • Causes corrosion of air or gas operated instruments, giving false readings, interrupting or shutting down plant processes

In almost every operation, clean, dry compressed air will result in lower operating costs. Dirt, water and oil entrained in the air will be deposited on the inner surfaces of pipes and fittings, causing an increase in pressure drop in the line which results in a loss of performance efficiency.

Liquid water accelerates corrosion and shortens the useful life of equipment and carryover of corrosion particles can plug valves, fittings and instrument control lines. When water freezes in these components, similar plugging will occur.

Common Leak Problem Areas

Air leaks are a significant source of wasted energy in a compressed air system, often wasting as much as 20-30% of the compressor’s output. Compressed air leaks can also contribute to problems with system operations, including:

  • Fluctuating system pressure, which can cause air tools and other air-operated equipment to function less efficiently, possibly affecting production
  • Excess compressor capacity, resulting in higher than necessary costs
  • Decreased service life and increased maintenance of supply equipment due to unnecessary cycling and increased run time

Proactive leak detection and repair can reduce leaks to less than 10% of compressor output. The most common leak problem areas are:

  • Couplings, hoses, tubes and fittings
  • Disconnects
  • Filters, regulators and lubricators
  • Open condensate traps
  • Pipe joints
  • Control and shut-off valves
  • Point of use devices
  • Flanges
  • Cylinder rod packing
  • Thread sealants

Once leaks have been repaired, the compressor control system should be re-evaluated to realize the total savings potential.  

Contact us to schedule a free compressor system assessment.