Principles of Operation

Last week, I wrote about frequently-asked-questions.  I really enjoy opportunities to engage in technical discussions with folks who want to know how a certain EXAIR product works, and, more importantly, how it will work for them.

Occasionally, we’ll get asked questions about the principle of operation, and, especially with our vacuum products, people will assume they operate on the Venturi principle (a constriction to fluid flow within a tube causes the velocity to increase and the pressure to fall), which is a very popular, tried-and-true method to create a vacuum.

Another way to do it, though, is to rely on the Coanda effect, which is the tendency of a stream of fluid flowing near a surface to follow the line of that surface, rather than its original course.  This is how our Air Knives turn a relatively small amount of compressed air into a tremendous amount of flow.  It’s also the way our Air Amplifiers work – when the compressed air leaves the internal nozzle and follows the internal surface (the Coanda profile) towards the outlet, it entrains a bunch of the existing air inside the product and takes it along, and a low pressure area (aka “vacuum”) is created.

Yet another way to do it is simply direct a high velocity of air towards the outlet.  The forceful exit of the air then entrains the air inside the item, creating a vacuum.  That’s how the Line Vacs, Chip Vacs, Heavy Duty Dry Vacs, and Vac-u-Guns work.  Fancy scientific principles aside, never underestimate the value of simple brute force!

That said, all of these products are quite similar in their basic construction.  The Air Amplifiers’ low pressure area allows it to pull an enormous amount of air through (albeit at a lower vacuum level), which is good for moving large quantities of air and airborne particulate.  The Line Vacs, Chip Vacs and Heavy Duty Dry Vacs don’t have as much vacuum flow, but are capable of pulling a pretty strong vacuum – as much as 144” H2O (-36 kPa), which is great if you’re vacuuming up, or conveying, solid materials.

For the record, our E-Vac Vacuum Generators use the Venturi principle to pull a strong vacuum of up to 27”Hg.  They’re ideally suited for a wide variety of applications such as: pick-and-place lifting, vacuum forming, mold evacuation, clamping/chucking, “hands-off” liquid sampling, and vacuum filling, just to name a few.

Strictly speaking, the Reversible Drum Vac operates on the Venturi principle as well, although the air path isn’t as straight forward as your plain old run-of-the-mill eductor type product.  That’s how it generates the vacuum to fill a drum with liquid.  Of course, to pump it out, with a simple turn of the knob, we’re back to good old brute force.

Regardless of the scientific principle behind the operation, if you have an application that requires pulling a vacuum, we can help…give us a call!

Russ Bowman
Application Engineer
EXAIR Corporation
(513)671-3322 local
(800)923-9247 toll free
(513)671-3363 fax

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