The Importance Of Properly Sized Compressed Air Supply Lines

EXAIR Corporation manufactures a variety of engineered compressed air products that have been solving myriad applications in industry for almost 37 years now.  In order for them to function properly, though, they have to be supplied with enough compressed air flow, which means the compressed air supply lines have to be adequately sized.

A 20 foot length of 1/4″ pipe can handle a maximum flow capacity of 18 SCFM, so it’s good for a Model 1100 Super Air Nozzle (uses 14 SCFM @80psig) or a Model 110006 6″ Super Air Knife (uses 17.4 SCFM @80psig,) but it’s going to starve anything requiring much more air than those products.  Since compressed air consumption of devices like EXAIR Intelligent Compressed Air Products is directly proportional to inlet pressure, we can use the flow capacity of the pipe, the upstream air pressure, and the known consumption of the EXAIR product to calculate the inlet pressure of a starved product.  This will give us an idea of its performance as well.

Let’s use a 12″ Super Air Knife, with the 20 foot length of 1/4″ pipe as an example.  The ratio formula is:

(P2 ÷ P1) C1 = C2, where:

P2 – absolute pressure we’re solving for*

P1 – absolute pressure for our published compressed air consumption, or C1*

C1 – known value of compressed air consumption at supply pressure P1

C2 – compressed air consumption at supply pressure P2

*gauge pressure plus 14.7psi atmospheric pressure

This is the typical formula we use, since we’re normally solving for compressed air consumption at a certain supply pressure, but, rearranged to solve for inlet pressure assuming the consumption will be the capacity of the supply line in question:

(C2 P1) ÷ C1 = P2

[18 SCFM X (80psig + 14.7psia)] ÷ 34.8 SCFM = 49psia – 14.7psia = 34.3psig inlet pressure to the 12″ Super Air Knife.

From the Super Air Knife performance chart…

This table is found on page 22 of EXAIR Catalog #32.

…we can extrapolate that the performance of a 12″ Super Air Knife, supplied with a 20 foot length of 1/4″ pipe, will perform just under the parameters of one supplied at 40psig:

  • Air velocity less than 7,000 fpm, as compared to 11,800 fpm*
  • Force @6″ from target of 13.2oz total, instead of 30oz*
  • *Performance values for a 12″ length supplied with an adequately sized supply line, allowing for 80psig at the inlet to the Air Knife.

Qualitatively speaking, if you hold your hand in front of an adequately supplied Super Air Knife, it’ll feel an awful lot like sticking your hand out the window of a moving car at 50 miles an hour.  If it’s being supplied with the 20 foot length of 1/4″ pipe, though, it’s going to feel more like a desk fan on high speed.

The type of supply line is important too.  A 1/4″ pipe has an ID of about 3/8″ (0.363″, to be exact) but a 1/4″ hose has an ID of only…you guessed it…1/4″.  Let’s say you have 20 feet of 1/4″ hose instead, which will handle only 7 SCFM of compressed air flow capacity:

[7 SCFM X (80psig + 14.7psia)] ÷ 34.8 SCFM = 19psia – 14.7psia = 4.3psig inlet pressure to the 12″ Super Air Knife.

Our Super Air Knife performance chart doesn’t go that low, but, qualitatively, that’s going to generate a light breeze coming out of the Super Air Knife.  This is why, for good performance, it’s important to follow the recommendations in the Installation Guide:

This table comes directly from the Installation & Operation Instructions for the Super Air Knife.
All Installation Guides for EXAIR Intelligent Compressed Air Products contain recommended air supply line sizes for this very reason.  If you have any questions, though, about proper compressed air supply, give me a call.

Russ Bowman
Application Engineer
EXAIR Corporation
Visit us on the Web
Follow me on Twitter
Like us on Facebook

Usefulness of a Coanda Profile

How did a past inventor help generate efficient compressed air products for EXAIR?  In the early 20th century, Henri Coanda who was a Romanian aeronautical engineer that built an experimental Coanda-1910 airplane.  There are some debates if the airplane actually flew, but he invented a curved surface for a wing to generate a Coanda effect. The Coanda effect is the “tendency of a fluid jet to stay attached to a convex surface”1.   Thus, a moving stream of fluid will follow the curvature of the surface rather than continuing to travel in a straight line.  The Wright Brothers who flew the first airplane in the state where EXAIR is located, Ohio, used the Coanda effect to create lift.  With a curved profile, the air will adhere to the surface, causing a low pressure which makes the airplane fly.

Standard Air Knife
Super Air Amplifier with shims

EXAIR uses this Coanda profile to make some of our Intelligent Compressed Air Products™.   Like the airplane wing, our curved surface will also create a low pressure.  How does this help?  Well, high pressure will always travel to low pressure.  Instead of lift, we use the low air pressure to entrain ambient air.  This ratio is what we call the amplification ratio.  The higher the amplification ratio, the higher the efficiency for a blowing device. Two main compressed air products that EXAIR manufactures use this type of profile; Air Knives and Air Amplifiers.  I will cover both below.

Compressed air flows through the inlet (1) to the Standard Air Knife, into the internal plenum. It then discharges through a thin gap (2), adhering to the Coanda profile (3) which directs it down the face of the Air Knife. The precision engineered & finished surfaces optimize entrainment of air (4) from the surrounding environment.

The Air Knives that use the Coanda profile blows air along the length of the knife at a 90o angle from the exit.  We offer two types; the Standard Air Knife and the Full Flow Air Knife.  The Standard Air Knives are made in Aluminum or Stainless Steel with blowing widths up to 48” (1219mm).  The inlet ports are at each end; so, the overall length is 1” (25mm) longer.  The Full Flow Air Knives have the port or ports on the back.  The air blows out the entire length of the air knife.  The maximum length is 36” (914mm).

Both types of air knives use the Coanda profile to generate a low pressure as the air exits the gap and “hugs” the curve (reference photo above).  This low pressure draws ambient air into the air stream at a 30:1 amplification ratio for both the Standard Air Knife and Full Flow Air Knife.  So, for every one part of compressed air, we entrain 30 parts of ambient air.  Besides efficiency, it also adds mass to the air stream for a hard-hitting force.  With this engineered profile, the air stream is laminar which gives a consistent force across the entire length and reduces noise levels.  Not only will they save you money,  but they are also OSHA safe.

Air Amplifiers use the Coanda Effect to generate high flow with low consumption.

The Air Amplifiers use the Coanda profile in a circular form to pull in dramatic amounts of free surrounding air.  The Coanda effect is able to generate a low pressure to blow air for cooling, cleaning or removing smoke and debris efficiently and quietly.  The Air Knives above blow a flat stream of air while the Air Amplifiers will blow a conical air stream.  They can reach amplification ratios up to 25:1. The Super Air Amplifiers use a patented shim to increase efficiency.

Unlike fans, they blow a laminar air stream for quick cooling.  They do not have any moving parts or motors to wear, so they are very quiet.  EXAIR manufactures five different sizes from ¾” (19mm) to 8” (203mm).  The Adjustable Air Amplifiers have a plug that can be adjusted to control the blowing force from a breeze to a blast.  For cleaning surfaces, this is a nice feature to “dial” in to exactly what you need.  We also manufacture five different sizes in aluminum and stainless steel ranging from ¾” (19mm) to 4” (102mm).  Both Air Amplifiers can be attached to ducts to remove debris, heat or smoke from the area.

Utilizing the Coanda effect allows for massive compressed air savings. Whether it is a flat or round air stream, EXAIR can do this with high amplification ratios.  If you would like to discuss further how our Air Knives or Air Amplifiers can help you in your applications, please contact us. An Application Engineer will be happy to help you.  History has shown us a way to increase efficiency when using compressed air.  And you can take advantage of it with the Coanda profile.  Thank you Mr. Henri Coanda.

John Ball
Application Engineer
Email: johnball@exair.com
Twitter: @EXAIR_jb

 

1note – Wikipedia – Coanda effect

EXAIR Products in Construction Industry: Super Air Knife Helps Steel Door Drying

A manufacturer of both residential and commercial steel doors used in the construction industry recently contacted me for help with an application in their manufacturing process. They make a wide variety of exterior and interior doors as well as some custom doors that are sold to builders across the country.

foyer-902404_1920

The raw material for the doors is formed, assembled, and welded together before it is then taken to a finishing step that involves grinding down the welds and sanding any rough spots on the door down to a smooth finish. This smooth finish creates a clean look and also helps with the application of paint at the end of the process.

After finishing, the doors are hung on an overhead conveyor where they pass through a machine that cleans off all of the surfaces and remain hanging until they dry. This air drying prevented them from continuously operating as they’d have to wait at least 10 minutes until the doors dried before they could apply any paint. In the summer, humid conditions in their plant further increased the time the doors took to air dry.

110048PKI
Super Air Knife w/ Plumbing Kit Installed

Rather than waiting to dry, they wanted to blow off any remaining water from both sides of the door just after the washing operation. The solution was to install (2) Model 110048PKI Super Air Knives on either side of the door to blow off residual water as it moved along the conveyor. Since the spacing in between doors was 12’, they didn’t want to have to operate the knives continuously and waste unnecessary compressed air.

With the doors traveling slowly at about 30 ft/min and a significant space in between them, they also went with a Model 9064 Electronic Flow Controller to keep the air on only when necessary. A standard door height is just under 7′. At the speed they were traveling, it would take roughly 14 seconds for each door to pass through the flow of the knives while 24 seconds pass with no door.

With a minimum 10 minute dry time without the Super Air Knives, the overall drying time was reduced to 38 seconds. That’s a 93.6% improvement in the overall time of their drying process! By improving the drying process, they were able to increase their production to 100 doors per 8-hr shift.

(2) 48″ Super Air Knives operating continuously at 80 PSIG would require 278.4 SCFM of compressed air. The average cost of compressed air is $0.25/1000 SCF. So what did this cost when operating continuously with a 38 second blowoff time?

0.633 min x 278.4 SCFM = 176 SCF/door

176 SCF x 100 doors per shift = 17,600 SCF

17600 SCF x ($0.25/ 1000 SCF) = $4.40/ 8 hr shift

Over the course of a year that equates to $1,144 in operating costs. With the EFC implemented, the blowoff time was reduced to just 14 seconds per door.

0.233 min x 278.4 SCFM = 65 SCF/door

65 SCF x 100 doors per shift = 6500 SCF

6500 SCF x ($0.25/1000 SCF) = $1.63/ 8 hr shift

Not only were they able to increase their production rate by implementing the Super Air Knife, but by taking it one step further with the EFC they reduced the overall operating costs for a full year to just $423.80.

efc_heroi

If you have a similar application in the construction industry and would like to speak to an Application Engineer please give us a call!

Tyler Daniel
EXAIR Corporation
E-mail: TylerDaniel@EXAIR.com
Twitter: @EXAIR_TD

Door photo courtesy of ErikaWittlieb via Pixabay

EXAIR’s Long Super Air Knives Dry Auto Bodies

I was recently contacted by an automobile manufacturer that was looking for a quote for a system of Super Air Knives for a current process they were replicating at a new facility. The customer had an existing application where they’re using the Super Air Knife to dry the body of the car after a washing operation and before it enters into an oven. Any large water droplets remaining when the body enters the oven cause water spots that must then be cleaned off, adding an additional step in their process.

SAK car blowoff2

The solution was working well to dry the bodies, they just needed a quote so that they could implement the very same process in the new plant. As this was an installation that had been in place for many years, they had an older style of Long Super Air Knife that consisted of two shorter knives coupled together. In 2014, EXAIR began manufacturing our Long Super Air Knives in one single piece (available from stock up to 108”!!).

So, now, rather than having two individually coupled knives they could order (1) single 84” knife with a consistent flow all the way across and no dead spots. They ordered one for the top, one for each side and replicated the already successful application.

EXAIR’s industry leading Super Air Knife dramatically reduces compressed air usage and noise when compared to other blowoff methods. The Super Air Knife is available in lengths ranging from 3”-108” and in Aluminum, 303 Stainless Steel, 316 Stainless Steel, and PVDF for corrosive applications. Even at high pressures of 80 psig, the Super Air Knife is able to maintain a sound level of just 69 dBA for most applications! Air is entrained from the ambient environment at a rate of 40:1, maximizing the force and flow from the Super Air Knife. In addition, these knives meet or exceed OSHA maximum dead-end pressure and noise requirements.

Adjustability of both the force and flow from the Super Air Knife is infinitely adjustable. Right out of the box from the factory the Super Air Knife comes stock with a .002” thick shim installed. This sets the gap between the body and cap of the knife and determines how much compressed air can flow through the precise, slotted orifice.

An accessory that EXAIR has available for the Super Air Knife is the shim set. For the aluminum knives, a .001”, .003”, and .004” plastic shims come in the shim set. To reduce the flow and force, a .001” can be used. If more force is required, a thicker shim can be installed. For the stainless steel and PVDF knives, (3) .002” shims are included in the set. Stainless steel shims for the stainless knives and a PTFE shim for the PVDF. These, as well as the plastic shims, can be stacked on top of one another to create an even larger gap. One thing that is important to keep in mind however, the larger the air gap the greater the air consumption. Installing a .004” shim in a Super Air Knife will double the force, flow, and consumption of the knife when compared to the stock .002” shim.

If you have a new application (or need to replicate an existing one) for the Super Air Knife, don’t hesitate to reach out to an EXAIR Application Engineer for assistance. With a highly-trained team coming from multiple different industry backgrounds, we’re ready to help.

Tyler Daniel
Application Engineer
E-mail: TylerDaniel@EXAIR.com
Twitter: @EXAIR_TD