Super Air Knife Math – When 72 + 72 = 75

The Super Air Knife is the latest generation of EXAIR engineered air knife that dramatically reduces compressed air usage and noise when compared to other blowoffs.

Super Air Knife Data

From the chart above, the Super Air Knife when supplied with 100 PSIG of compressed air has a sound level of just 72 dBA (A-weighted decibel scale) when measured from 3′ away.  72 dBA is a moderate sound level, and some common comparisons are ‘normal speaking voice’ at 70 dBA and ‘living room music’ at 76 dBA.

For many processes, such as a bottling line drying operation, a pair of the air knives delivers the best performance. When asked, “what is the sound level for (2) of the knives,” a little Acoustic Engineering is in order. Because the decibel scale is logarithmic, the result is not as simple as adding 72 + 72 = 144.  144 dBA is in the range of a jet aircraft take off! Thankfully, both the actual sound level and the numerical value are determined another way.  I’ll spare you a lot of the math but the equation is as below.

Capture

… where SL1, SL2, SL3 are the sound levels in dBA of the each sound makers, for as many that are being combined.

In the case of (2) Super Air Knives operated 100 PSIG, the combined sound works out to be a quiet 75.0 dBA — a powerful, efficient and quiet product ideal for many applications and process within the manufacturing environment.

Super Air Knife

Super Air Knife

As a helpful rule of thumb- combining any (2) items will yield an increase of 3 dBA, combining (3) results in a rise of 4.8 dBA, and combining (4) results in a 6 dBA rise over just (1) of the items.

The Super Air Knives have been successfully used in a wide range of applications, including part drying, sheet and conveyor cleaning, web cooling, scrap removal, pre-paint dust blowoff, and many, many more.

To discuss your application and how an EXAIR Intelligent Compressed Air Product can make your process better and quieter, feel free to contact EXAIR and myself or one of our other Application Engineers can help you determine the best solution.

Brian Bergmann
Application Engineer

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Selecting An EXAIR Air Knife

Many times we receive a  call from a customer looking for an Air Knife but they are unsure which design is the best to suit their needs. With 3 options to choose from, the Super Air Knife, Standard Air Knife and Full-Flow, it can seem like a somewhat daunting task so lets take a look at some of the key differences between the units. We keep all of these models in stock and can ship same day on orders we receive by 3 pm.

Super Air Knife

EXAIR Super Air Knife

Let’s start with our most popular choice, the Super Air Knife. The Super Air Knife is our most efficient unit, using a 40:1 amplification rate of entrained surrounding air to compressed air, it consumes only 2.9 SCFM per inch @ 80 PSIG while maintaining a low sound level of 69 dbA. This unit produces a laminar airflow across the entire length of the knife and there are air inlets on each end, as well as on the bottom. We offer lengths from 3″ up to 108″ in aluminum, 303ss, or 316ss. Additionally we offer lengths up to 54″ in PVDF (Polyvinylidene Flouride) for applications requiring superior chemical resistance, like those associated to acids, solvents or aggressive chemicals. There are 1/4-20 tapped holes on the bottom of the knife which can be used for mounting. We recommend the Super Air Knife most often because it uses the least amount of compressed air and has the most even airflow from end to end.

Std Air Knife

Standard Air Knife

Secondly we offer our Standard Air Knife which provides a 30:1 amplification rate, consuming slightly more compressed air at 3.4 SCFM per inch @ 80 PSIG. These units are louder at 83 dBA and feature air inlets on each end. Lengths available from 3″ up to 48″ in aluminum or 303ss construction.  The airflow length is 1″ smaller than the length of the knife (1/2″ of no flow on each end), for example a 12″ Standard Air Knife has a 13″ physical length with a 12″ airflow length. This is the first knife we ever manufactured and is a solid choice with good performance.

Full-Flow

Full-Flow Air Knife

Lastly, the Full-Flow Air Knife. Again providing a 30:1 ratio of entrained ambient air to compressed air, has the smallest dimensional footprint. Air consumption is slightly less than the Standard Air Knife at 3.1 SCFM per inch @ 80 PSIG with an airflow length equal to the length of the knife. We offer lengths from 3″ up to 36″, again in aluminum and 303ss and the air inlets are on the back of these units. The Full Flow Air Knife fills the need for customers with limited mounting space and who cannot fit a Super Air Knife into the desired location.

Hopefully this information will help in making the best decision to fit your needs. Of course if you still need additional support, please don’t hesitate to contact one of our Application Engineers for assistance.

Justin Nicholl
Application Engineer
justinnicholl@exair.com
@EXAIR_JN

Thinking “Inside” the (Election) Box

With Election Day coming up in November and everyone gearing up for next year’s presidential race, a thought popped into my head about the infamous Florida hanging chads during the Bush-Gore Race years ago. What if the Florida Election Board had installed an EXAIR product to blow the chads away as they were punched through the ballet? True, I do not think it would have resolved all the chads still hanging, but it might have blown enough away that there would have been less questionable votes. Although not really practical – air compressors at each booth?! – and likely not feasible or economical, it still is an interesting idea. Running with it a bit, what could they have used? EXAIR offers many different ways to accomplish blowoff. In this case, two options come to mind: air knife and safety air gun.

A standard air knife (dictated by budget, after all), the length of the ballet, could be installed on one the side of the election booth. As the chads are pushed through, the air would blow underneath to push them into a trough on the other side of the booth. Unobtrusive, easy, no mess.

The second option is the safety air gun. This is a bit more manual and would probably need to have the voters trained in use to insure privacy. The soft grip version is a definite; Florida has more senior citizens than any other state and comfort is a must. In this scenario, the voter would vote, then pick up the ballet and use the air gun to spray the chads off to one of the booth’s back corners were the chads would drop down into a collection chute to the rear underneath. I feel this method would not be quite as successful as the first, for a multitude of reasons – dexterity, blowing the ballet away, potentially messy, voter misconduct, etc.

In the years since, states have gotten away from using chad-type ballets. But if you are reading this and your state is still hanging and stuck with chads, you may want to suggest an EXAIR method of helping out in the next election. Just imagine the headline: “Compressed Air Decides Election!”

John Pinchek
Application Engineer
johnpinchek@exair.com
@EXAIR_JP

Full-Flow Air Knife Dries Copper Strip

Last week I was working with a customer who was using our 36″ Full-Flow Air Knife to dry a flat copper strip as it exited the rinse cycle of their process. The customer chose the Full-Flow design due to it’s small profile, making it easier to fit into the tight space available to mount to their machine. The customer stated that they flow tested the knife before installation and the knife “worked great” but once mounted, the flow was reduced significantly. They were thinking of returning the unit under our Unconditional 30 Day Guarantee but I offered to help troubleshoot the unit to see if we couldn’t relieve their issue(s).

Full-Flow

The Full-Flow Air Knife is available up to 36″ in either aluminum or 303ss construction.

When they tested the unit external to the machine they were using 1″ hose (our recommendation for a 36″ Air Knife) running to a tee, which stepped down to 1/2″ ID hose going to both rear inlets on the back of the knife. But when they installed the knife, due to space limitations, they reduced the main supply to 3/8″ tubing and plumbed only 1 inlet using a quick disconnect. This explained some of the low output flow with the unit. Using undersized supply lines and quick disconnect cause significant pressure drops due to their small inside diameters. When this occurs, you aren’t able to flow enough volume of air (SCFM) to the knife, which results in reduced performance and uneven flow.

The second issue was how they had the unit mounted to the machine. Wanting to keep the air inlets easily accessible, they mounted the face of the knife (the surface the compressed air runs along) right up to the outside wall of the machine, leaving just a small gap for the output flow and built a protective shield around the unit. The Full-Flow Air Knife will entrain 30 parts of surrounding, ambient air for every 1 part (SCFM) of compressed air used. With the unit being unable to entrain any free air, the output flow is further diminished.

How the Standard Air Knife Works

Illustration showing how the Standard and Full-Flow Air Knives operate.

After increasing the supply line to both inlets, removing the quick disconnect and protective shield and moving the knife back to allow for the air entrainment, the customer called back to advise that the strip was now completely dry.

If you are experiencing reduced performance or need help with the installation of your EXAIR product, give us a call at 1-800-903-9247.

Justin Nicholl
Application Engineer
justinnicholl@exair.com
@EXAIR_JN

 

How To Choose An Air Knife

The EXAIR Super Air Knife has a prominent place near the front of our catalog, and THIRTEEN pages of photos, application details, performance data & specifications. It’s the most efficient and quietest product of its kind on the market, and our most diverse product offering in terms of size range, operational adjustability, materials of construction, and accessories available. For almost any general industrial air blow off application, the EXAIR Super Air Knife is the superior choice in terms of air usage, sound level, and capability.

EXAIR Super Air Knives come in a wide range of lengths, for a wide range of possibilities.

EXAIR Super Air Knives come in a wide range of lengths, for a wide range of possibilities.

As tireless champions of the causes of reducing air consumption and noise, we’re always going to promote these benefits of the Super Air Knife. Still, a caller asked me the other day, “Well, why do you still make the others?”…meaning, of course, our Standard and Full Flow Air Knives. Why, indeed:

*Given the same air supply pressure, the Standard Air Knife generates the highest force of our three styles. The amount of force applied isn’t always a prime consideration…if you think about one of the more “textbook” applications for an Air Knife, it doesn’t take a great amount of force to blow off dust and light debris from a conveyor belt…certainly this is a case where efficiency factors in: the lower air consumption of a Super Air Knife can pay for the cost difference between it and a Standard Air Knife in as little as three months of operation.

The Standard Air Knife has the highest force, for when it's needed.

The Standard Air Knife has the highest force, for when it’s needed.

Of course, if you’re blowing stubborn debris out of tight spaces, like gummy, greasy dirt that’s accumulating in the recesses of a finned tube heat exchanger, that extra force can make all the difference. No; the Standard Air Knife isn’t as efficient or quiet as the Super Air Knife, but it’s still a far cry better than a drilled pipe.

*While the Super Air Knife is pretty compact – you only need a few square inches of profile area to successfully mount it – the Full Flow Air Knife is even smaller, requiring not much more than one square inch of profile for mounting. With ports on the rear face (instead of the ends & bottom for the Super Air Knife,) they can fit in very tight quarters.

Low profile and lightweight, the Full Flow Air Knives are a great fit for tight quarters.

Low profile and lightweight, the Full Flow Air Knives are a great fit for tight quarters.

The Full Flow Air Knife is also the lightest weight for a given length. A 36” Aluminum Super Air Knife, for instance, weighs about 8lbs. The 36” Aluminum Full Flow Air Knife weighs less than 4lbs. Most of the time, 8lbs is a very manageable amount of mass to support, but there are situations where every ounce matters, and if yours is one of them, you’re looking at the Full Flow Air Knife all the way.

*The biggest (in the most literal sense) factor in Air Knife selection is, well…size. We make the Standard Air Knives in lengths to 48”, and the Full Flow Air Knives come as long as 36”. The Super Air Knives, however, are stocked in lengths from 3” to 108”, and can be coupled together for as long of an uninterrupted, steady, laminar air flow as you need.

At the end of the day, a majority of blow off applications can be handled just fine with any of our Air Knives. If you’d like to discuss your application and see which one is best for you, give us a call.

Russ Bowman
Application Engineer
(513)671-3322 local
(800)923-9247 toll free
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Things Are Not Always As They Seem

A magician got a job on a cruise ship, entertaining the passengers on deck throughout the day, and performing a big nightly after dinner show. The Captain sat in the front row, and brought his pet parrot to see the show every night. After a couple of performances, the parrot started to figure out some of the magician’s tricks, and would cry out “The card’s up his sleeve!” “The ball’s in his other hand!” “There’s a fake bottom in the box!”  This irritated the magician to no end, but despite his protests, the Captain continued to bring the parrot to every show.

Then one night, the ship hit an iceberg and sank. The magician and the parrot ended up in the same lifeboat, where they sat, quietly glaring at each other. Hour upon hour passed in complete silence. Just before dawn, the parrot finally said “OK; I give up. What did you do with the ship?”

Magicians, of course, are the masters of all things “not as they seem,” using sleight-of-hand to create illusions or distractions. That means we see what they want us to see, we’re entertained, and their mission is accomplished.

The laws of physics mean that things are not always as they might seem as well. This morning, I had the pleasure of discussing an Air Knife application with a customer who intended to mount a Standard Air Knife as close as possible to his material, in order to provide the highest possible force from the air flow. The thought was, the closer the better, right? Well…

It turns out, this Air Knife was tested at distances from 3mm – 30mm (about 1/8” – 1”) from the target. The amount of force applied actually INCREASED with the distance over that range. His thinking was, with the velocity of the air flow being the highest, right at the outlet of the Air Knife, this would be where the force was greatest too. And, all other things being equal, this would be true.

The velocity of the air flow exiting our Air Knives can be as high as 13,000 feet per minute, and it’s not slowing down one bit over an inch of travel…not to any degree that we have an instrument to measure, anyway. The Standard Air Knife, however, entrains air from the surrounding environment…in fact, at 6″ away, it’s actually entrained 30 TIMES the amount of air that’s being supplied from your compressed air system. This is a TREMENDOUS increase in the mass flow rate. So, if you have a BUNCH more air hitting the target at the same speed, it’s going to exert a proportionately higher force.

How Std AK works

After explaining this to my customer (who installs these on chemical processing machinery), he was then able to enlighten HIS clients to the benefits of letting a little physics do the heavy (or not so heavy) lifting. In this case, the unexpected increase in force they got by moving the Air Knife about ½” away meant they could actually lower their compressed air supply pressure, conserving a great deal of air in this continuous blowing application.

Do you want to know how EXAIR, our Intelligent Compressed Air Products, and the laws of physics can work wonders in your facility, give us a call. No sleight-of-hand or prestidigitation required, but we’re willing to learn!

Russ Bowman
Application Engineer
EXAIR Corporation
(513)671-3322 local
(800)923-9247 toll free
(513)671-3363 fax
Web: www.EXAIR.com
Twitter: twitter.com/exair_rb
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