Centrifugal Air Compressors: How Do They Work?

Centrifugal air compressors are one example of dynamic style air compressors. The dynamic type of compressors have a continuous flow of air that has its velocity increased in an impeller that is rotating at a higher speed. The kinetic energy of the air is increased due to the increase in velocity and then becomes transformed into pressure energy through the use of a volute chamber, or a diffuser. The volute chamber is a curved funnel that increases in surface are as it approaches the discharge port. This converts the kinetic energy into pressure by allowing the velocity to reduce while the pressure increases. Approximately 1/2 of the energy is developed in the impeller and the other half is developed in the volute chamber or diffuser.

1 – Basic Centrifugal Air Compressor

The most common centrifugal air comppressor has between two and four stages in order to generate pressures up to 150 psig. A water cooled inter-cooler and separator is placed between each stage in order to remove condensation and cool the air down prior to being passed on to the next stage. These compressors still have advantages and some disadvantages. The list below showcases just a few.

Advantages:

  • Lubricant-free air is generated
  • Complete packages up to 1,500 hp
  • Initial costs decrease with increase in compressor size
  • No special foundations or reinforcements needed

Disadvantages:

  • Specialized maintenance requirements
  • Higher initial investment
  • Unloading/waste of air required to drop system pressures

To determine which type of compressor may be best suited for your facility, we suggest to locate and contact a compressor sales company in your geographic area. When it comes to determining the volume of air required to operate the EXAIR products and even some other point of use compressed air applications, EXAIR’s Application Engineers can help you determine the volume you will need to ensure the compressor is sized appropriately. If you would like to discuss any other point of use application, please contact us.

Brian Farno
Application Engineer
BrianFarno@EXAIR.com
@EXAIR_BF

1 – Dugan, Tim PE – Basic Centrifugal Air Compressor, Compressed Air Best Practices; retrieved from https://www.airbestpractices.com/technology/air-compressors/centrifugal-air-compressor-controls-and-sizing-basics

Air Knife Shim Adjustment can be Key to Successful Applications

On January 2, 1960 Little Anthony & The Imperials appeared on The Dick Clark Saturday Night Beech-Nut Show to sing Shimmy Shimmy Ko Ko Bop. While I wasn’t around at that time, I have heard the song quite a few times and get it stuck in my head more than I have heard it. What does that song and EXAIR have to do with each other? Well, we shimmy shimmy Super Air Knives to dramatically increase or decrease their flow and force.

The stock shim that is assembled in every Super Air Knife is a .002″ (0.05mm) thick. This sets a continuous opening the full length of the knife that drives the performance of the knife. The shim sets the gap height between the cap and the body of the Super Air Knife. If we evaluate a 24″ Super Air Knife with the stock shim installed we could calculate the airflow opening of the knife as the surface area of a rectangle.  To obtain the surface area we take the length of the air knife times the thickness of the shim.  See the example below.

As you can see with the stock .002″ thick shim installed we are actually operating at a surface area opening of 0.048 square inches.  If we were to install the .004″ thick shim into the knife then we would double the height which in turn doubles the surface area, shown below.

This doubling effect will increase the force out of the Super Air Knife when applications require more power.  Thinning out the shim will have the exact opposite effect, if the shim thickness is reduced to .001″ thick then the air consumption and force will be reduced.

Changing the shims out of the Super Air Knives is a fairly simple task as shown in the video below.  Installing a different thickness of shim is a coarse adjustment to the volumetric flow needed for your application.  Then a pressure regulator can be used to fine tune the needed force and flow for the ideal setting to meet your needs, and operate at maximum efficiency for the application.

If you would like to discuss this further or even see what kind of custom thicknesses we can offer on the shims to truly make a tailor fit Super Air Knife for your application, please contact us.

Brian Farno
Application Engineer
BrianFarno@EXAIR.com
@EXAIR_BF

 

Little Anthony & The Imperials “Shimmy Shimmy Ko Ko Bop” – [Merlin] XelonEntertainment, WMG (on behalf of Turntable Recordings LTD); ARESA, LatinAutor, União Brasileira de Compositores, Spirit Music Publishing, UNIAO BRASILEIRA DE EDITORAS DE MUSICA – UBEM, Abramus Digital, BMI – Broadcast Music Inc., and 4 Music Rights Societies – https://www.youtube.com/watch?v=5mLjZRAXRRA

More Power May Not Be The Solution

I can’t tell you how much it pains me to write this after last week’s blog. But, if we’re being honest here, every Tim “The Tool Man” Taylor (“More Power!”) does indeed need an Al Borland (“I don’t think so, Tim.”) As evidence of this, I had an opportunity to provide reasoned advice to a caller on the tech support line this week:

They had just purchased a Model 110224 24″ Aluminum Super Air Knife Kit. The flow it produced wasn’t powerful enough for their needs, so they installed extra shims from the Shim Set (which comes with the Kit) – increasing the shim gap to 0.009″ (which can produce a great deal more air flow and force)…more power, right?

Super Air Knife Kits include a Shim Set, Filter Separator, and Pressure Regulator.
Super Air Knife Kits include a Shim Set, Filter Separator, and Pressure Regulator.

Unfortunately, not. The Super Air Knife makes a hard hitting curtain of air when supplied properly…but it’s going to need a 1/2″ pipe (ID of ~5/8″) to carry enough compressed air flow to make that happen. Turns out, they were using 1/4″ tubing, which wasn’t even getting enough compressed air flow to the unit with just the 0.002″ shim installed. Putting in the extra shims actually made that worse. Once they ran a 3/4″ hose to the Air Knife (and took out those extra shims,) they were actually able to regulate the air supply back to about 60psig, which provided a strong enough air flow to solve the application.

This table comes directly from the Installation & Operation Instructions for the Super Air Knife.
This table comes directly from the Installation & Operation Instructions for the Super Air Knife.

Sometimes, though, compressed air product applications DO come down to a need for more power.  Next week, I’ll tell you about a caller who said he needed “the biggest and most powerful” Safety Air Gun we had – and unlike the last time I wrote a blog about that – he was RIGHT.

Russ Bowman
Application Engineer
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Darn Right, More Power

“Home Improvement” was one of the more popular TV shows of the 1990’s – the lead Character (I capitalized that on purpose,) Tim “The Toolman” Taylor, hosted a handyman show with his skilled & more sensible sidekick, Al Borland. Tim’s mantra, “More Power,” was often tempered by Al’s quintessential retort of “I don’t think so, Tim.” For your viewing pleasure, here’s a collection of (more than) a few times when Al’s warning went unheeded.

When discussing compressed air product applications, I’m often asked if EXAIR has something with “more power” than what the caller is currently using.  Sometimes, it’s even an EXAIR product that’s not giving the results they want.  Regardless, the answer is usually “darn right, we do!”

This was the case recently, when I had the pleasure of actually doing a conveyance test in our shop for a customer.  The product was broken glass, and they wanted to move a fair amount of it, in a hurry.

Last year about this time, I wouldn’t have even recommended a test of the product; our Model 150200 2″ Heavy Duty Line Vac was our epitome of “More Power.”  Then, earlier this year, we introduced the Model 150300 3″ Heavy Duty Line Vac (also a 2-1/2″ model).

Yeah, we really don't have an "Al Borland" character on the EXAIR team...2" Heavy Duty Line Vac (left;) the new 3" model (right.)
2″ Heavy Duty Line Vac (left;) the new 3″ model (right.) Yeah, we really don’t have an “Al Borland” character on the EXAIR team…

The results were conclusive, and dramatic.  The 2″ Heavy Duty Line Vac moved the broken glass at a rate of 10.8 lb/min. Considering that included a 15 foot vertical rise, that’s not bad at all.  Based on the difference in conveyance air flow alone (which we use as a VERY rough estimation,) I expected an increase of 40-50% with the new 3″ model.  Instead, I could almost hear Tim Allen’s signature grunt as the 3″ Heavy Duty Line Vac reached a conveyance rate of 24 lb/min.  More power, indeed.

If you’d like to discuss an air operated conveyor application, or 1990’s sitcoms, give me a call.

Russ Bowman
Application Engineer
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