Air Compressor Introductory Terms & Concepts

Posted on: July 7, 2015

Does your company have a new crew of salespeople? This post is packed with introductory terms and concepts, and will help your rookies sound like pros when educating end users. 

According to Merriam-Webster’s Dictionary, compressed air is defined as air under pressure greater than that of the atmosphere. Compressed air can also be described as being free air that has been pressed into a volume smaller than it normally occupies. As it exerts pressure it performs work when released and allowed to expand to its normal free state. In today’s blog post, you will learn the basics of compressed air which will increase your credibility when speaking to clients about Quincy compressors. 

Why is compressed air used and who uses it? Since compressed air is essentially stored energy, there are numerous industries that use compressed air for various applications. It supplies motive force, and is preferred to electricity because it is safer and more convenient. Compressed air is the 4th utility to industry and 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 produces smooth translation with much more uniform force. Compressed air equipment can be more economical, and more durable without the shock hazard of electricity or the explosion hazard of oil. From a production assembly line to laboratories to heavy construction, compressed air can be used in endless industries.

Below are a list of examples in which compressed air can be used: 

  • Production Line Tools 
  • Automation & Assembly Stations
  • Plant Maintenance 
  • Chemical Manufacturing
  • Aircraft Mfg.
  • Automobiles
  • Beverages
  • Agriculture
  • Cement
  • Foundries
  • Plastics
  • Construction 
  • Hospitals
  • Monuments
  • Power Plants
  • Sewage Plants


The ability of a compressor to supply energy is expressed in both cfm and psig. CFM or Cubic Feet Per Minute is the volume of air measuring the compressors capabilities. The amount of 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 compressors capabilities, and PSIG means pounds per square inch gauge. Compressed air is usually 100 pounds over atmospheric pressure, or PSIG. Atmospheric air can be compressed in several ways: Positive Displacement Compressors, machines in which successive volumes of air are confined within a closed space and elevated to a higher pressure; Dynamic Compressors, machines in which air is compressed by the mechanical action of rotating impellers imparting velocity and pressure into the air; Centrifugal Compressor, which operates like a fan where the flow through the compressor is turned perpendicular to the axis of rotation. The volume (measured in CFM) required determines the size of the compressor needed to do the job. 

For example, a five horsepower compressor will supply 20 CFM at 100 PSIG. A 200 HP compressor will supply 1,000 CFM at 100 PSIG. So, the more volume, the faster the job gets done. In addition, greater pressure increases the force or torque. Some tools, motors, or hammers will not operate without sufficient volume, so it is very important to know what type of compressor to recommend for a specific application. 

Moisture in compressed air can cause big problems Hot air holds more water vapor, so it is vital to performance to make sure the air is cooled and the moisture is removed. To do this, an air cooler aftercooler, moisture separator and refrigerated air dryer are used. Some problems caused by water in compressed air include: maintenance and war increases; air equipment becomes sluggish; rust; air line freeze; shorter air tool life. 

Don’t forget that supplying compressed air is not free. The cost of compressed air can be one of the most expensive sources of energy in a plant. To calculate the cost of compressed air in a facility, use the formula shown below:

Cost ($) =

(bhp) x (0.746) x (# of operating hours) x ($/kWh) x (% time) x (% full load bhp)

Motor Efficiency

Where bhp = Compressor shaft horsepower (frequently higher than the motor nameplate horsepower = check equipment specification) Percent time = percentage of time running at this operating level Percent full-load bhp = bhp as percentage of full-load bhp at this operating level Motor efficiency = motor efficiency at this operating level.