Compressed Air Basics, Part 11: Other Technologies

In the previous posts, we went several different technologies in the compressed air world.  There are other technologies that exist, but they are a small percentage of the air compressors/blowers/vacuum pumps out there. 

Centrifugal Air Compressors

Centrifugal compressors use the same technology as jet engines.  They are dynamic compressors.  One or more impellers spin really fast, accelerating the air.  Then the air is forced through a diffuser, which is a smaller area.  The speeding up of the air and then slowing it down causes the pressure increase.  These are usually huge air compressors, hundreds of horsepower, and they're designed for large, continuous duty air use.   They're sometimes called radial compressors.




Below is a picture of a multistage centrifugal with several impellers and diffusers.  The pressure gets higher as it goes through each diffuser.

Axial Air Compressors

 Much like the centrifugal compressors above, these are large dynamic compressors and this technology is also used in jet engines.  They tend to be even larger than centrifugal compressors.  This technology is also common in steam and natural gas use.

The compressors are called axial because the air flows down the axis of the compressor.  You can see a good example of the air flow in this video.

Instead of using diffusers to slow down the air, the axial compressor has alternating rows of rotating and stationary elements.  The air gets sped up and then slowed down over and over.

 

Peristaltic Air Compressors

From the biggest air compressors (centrifugals and axials), we now go to one of the smallest compressors, the peristaltic.

Basically a rotor with one or more lobes squeezes a tube with air in it, moving the air from the inlet to the discharge.  These are more commonly used for juice and pizza sauce than they are for compressing air.

Helical Lobe Compressors

This technology mixes the rotary screw with the rotary lobe.  There is a gap in psi between a rotary lobe blower's maximum  psi and the psi where a rotary screw is no longer energy efficient (on the lower range of its psi).  This technology is designed to fill that gap.  Here is what the rotors look like.

Image courtesy of Aerzen USA

Linear and Vibrating Armature Compressors

Image courtesy of Gast Mfg

These are very similar to diaphragm compressors.  They are positive displacement compressors that use alternating current to move a piston, diaphragm or shuttle.  It compresses the air in the same manner that a diaphragm pump does.  It just uses electromagnetic force to move the components. 

Guided Rotor Compressors

Image courtesy of Combined Heat & Power, Inc.

This is another positive displacement rotary compressor, and this one is based upon an envoluted trochoid geometry.  Wikipedia says that "the compression volume is defined by the trochoidally rotating rotor mounted on an eccentric drive shaft."

In simple English, the thing in the middle spins and reduces the volume of the air, which causes an increase in pressure.


I've never personally seen one for compressed air use yet, but they do exist.  According to the literature of the companies that make them, their target applications are hydrogen and natural gas compression.  Like the hybrid screw-lobe above it's an emerging technology in the compressed air world, so time will tell how it fits in.

Trompes

A trompe was a way to compress air and other gases prior to electricity.  You can read more about them here.  In fact trompes helped power some of the first electricity generating plants.

It uses falling water to compress air.

One of the more recent ones that was used industrially is now a tourist attraction, and you can see it here.


Just because this blog, compressor classes or compressed air seminars may group a compressor technology into the dreaded "other" category,  it doesn't mean that technology is useless.  They are not any better or worse than the technologies I highlighted in previous weeks.  Every technology has its use.  These compressors are made for a reason and they often are the best choice for special applications.  I grouped them here because they are a small percentage of the air compressors in use today. 

There are many situations where one of the above technologies will be either be the most efficient or most effective way to compressor air - even a trompe .... if you happen have a waterfall handy and need to ventilate a mine or smelt iron.