Air Compressor Review

Hydraulic and Pneumatic Knowledge

In general an air compressor (gas compressor) is a machine that pressurizes or compresses air. The compressed air is is then delivered to the tool or machine or stored as potential energy in a pressure chamber or tank for later use. There are many industrial and consumer machines that will provide stored compressed or high volume kinetic air compression. These machines can divided into either positive-displacement or non-positive displacement types.

An air or gas compressor machines are typically powered by electrical motors, gas or diesel engines.

Positive displacement air compressors work by forcing air into a closed or sealed volume that reduces the volume to effect the compression. Reciprocating piston-type air compressors use this principle. They use valves similar to a reciprocating engine (four stroke) to draw ambient air in and then displace the air into a holding chamber through a one-way valve.

Air compressors used in high volume compressed gas industrial applications often have multiple stages. Each stage elevates the pressure of the air or gas. Also, multiple stage methods may be used for reliability.

The three principle machine methods to compress air are:

  • Rotary Vane - Utilizes rotating vanes to displace and compress air or gas. Multiple and single stage designs are available.
  • Screw Rotary - Use two screws similar to a drill bit and spin in synchronous and compress the air or gas. Multiple and single stage designs are available.
  • Piston - Also called "Reciprocating Compressors" . Multiple and single stage designs are available. This type of air compressor is most commonly available to consumers through retail sources.

Industrial uses of air compressors include:

  • To supply clean air into a storage scuba divers tank for breathing.
  • To supply pressurized air to power and operate pneumatic tools.
  • To supply large volumes of pressurized air for industrial processes and machines.

Rating or specifications of air compressors:

When specifying or determine your needs for an air compressor one need to know and understand their requirements. Air compressors are typically rated in CFM, PSI and the horsepower that is available to drive the compressor pump.

CFM = Cubic feet per minute. This and the operating PSI is the most important specification one needs to consider. Every industrial machine, tool, or compressed application used needs to investigated and the CFM requirements tallied. One needs to determine if these tool or industrial applications are going to be used simultaneously or individually. The total CFM required to operate these machines plus a safety factor needs to be understood so that the the air compressor can do the job it was meant to do. It is common practice to have a capacity of not less than 150% of maximum required CFM.

Therefore: Total maximum CFM determined x 1.5 = Total CFM for the system (installed).

Typical hand tools will need between .3 CFM to 15 CFM to work properly. GO look at the equipment specifications or your owners handbook.

Note; Be aware that the size and length of the compressed air supply lines (pipes) should be sized properly as small and long pipes could result in an unacceptable pressure (PSI) and volume drop (CFM) due to pipe losses.


Yes - Larger diameter (ID) and shorter pipes are better to prevent operating pressure and volume loss. ID = Inside Diameter

PSI - pounds per square inch. The is the rated pressure at the rated volume the air compressor will deliver. Most if not all air compressors will have a pressure regulator. One needs to determine the operating pressure of the machine tools used in the pneumatic system to specify (size) the air compressor correctly. Most hand tools and industrial machines will have a range of pressures in which they will operate efficiently.

HP = Horsepower. This is of particular interest as horsepower is a reasonably good indicator of how hard the air compressor will have to work to deliver the CFM and the rated pressure. In general this is also an indicator of the life span of any performance group of air compressors. When given a choice between two air compressors with the same rated CFM and PSI, usually the compressor with the highest HP will last the longest, however it will cost more.