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
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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 and the Hierarchy of Controls

The CDC (Center for Disease Control) published a useful guide called “Hierarchy of Controls” that details (5) different types of control methods for exposure to occupational hazards while showing the relative effectiveness of each method.

NIOSH_Hierarchy_of_Controls
Hierarchy of Controls

 

The least effective methods are Administrative Controls and Personal Protective Equipment (PPE). Administrative Controls involve making changes to the way people perform the work and promoting safe practices through training. The training could be related to correct operating procedures, keeping the workplace clean, emergency response to incidents, and personal hygiene practices, such as proper hand washing after handling hazardous materials. PPE is the least effective method because the equipment (ear plugs, gloves, respirators, etc.) can become damaged, may be uncomfortable and not used, or used incorrectly.

In the middle range of effectiveness is Engineering Controls. These controls are implemented by design changes to the equipment or process to reduce or eliminate the hazard. Good engineering controls can be very effective in protecting people regardless of the the actions and behaviors of the workers. While higher in initial cost than Administrative controls or PPE, typically operating costs are lower, and a cost saving may be realized in the long run.

The final two, Elimination and Substitution are the most effective but can be the most difficult to integrate into an existing process. If the process is still in the design phase, it may be easier and less expensive to eliminate or substitute the hazard. Elimination of the hazard would be the ultimate and most effective method, either by removing the hazard altogether, or changing the work process so the hazard is no longer part of the process.

EXAIR can help your company follow the Hierarchy of Controls, and eliminate, or substitute the hazards of compressed air use with relative ease. 

Home of Intelligent Compressed Air Products

Engineers can eliminate loud and unsafe pressure nozzles with designs that utilize quiet and intelligent compressed air products such as Air NozzlesAir Knives and Air Amplifiers. Also, unsafe existing products such as air guns, can be substituted with EXAIR engineered solutions that meet the OSHA standards 29 CFR 1910.242(b) and 29 CFR 1910.95(a).

In summary, Elimination and Substitution are the most effective methods and should be used whenever possible to reduce or eliminate the hazard and keep people safe in the workplace. EXAIR products can be easily substituted for existing, unsafe compressed air products in many cases. And to avoid the hazard altogether, remember EXAIR when designing products  or processes which require compressed air use for cooling, cleaning, ejection, and more. 

If you have questions about the Hierarchy of Controls and safe compressed air usage from any of the 15 different EXAIR Intelligent Compressed Air® Product lines, feel free to contact EXAIR and myself or any of our Application Engineers can help you determine the best solution.

Jordan Shouse
Application Engineer

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Hierarchy of Controls Image:  used from  Public Domain

Why Use EXAIR Super Air Knives: Return on Investment

Return on Investment, or ROI, is the ratio of profit over total investment.  Many people use it to check stocks, financial markets, capital equipment, etc.  It is a quantitative way in determining the validity for an investment or project.   You can use the ROI value to give a measurable rate in looking at your investment.  For a positive ROI value, the project will pay for itself in less than one year.  Any negative values would represent a high-risk investment.  In this blog, I will compare the ROI between an EXAIR Super Air Knife to a common drilled pipe.  Let’s start by looking at Equation 1 to calculate the Return on Investment:

Equation 1:  ROI = (Total annual savings – Total Project Cost) / Total Project Cost * 100

The Total Project Cost is the cost of the product with the labor to install.  In our example, we will use a 24” (610mm) wide blow-off device.  One device will be an inexpensive drilled pipe and the other will be a high-efficiency EXAIR Super Air Knife.  The drilled pipe had (48) 1/16” (1.6mm) diameter holes spaced ½” (13mm) apart.  EXAIR manufactures the model 110024 Super Air Knife with a .002” (.05mm) slot along the entire length.  Both have a blowing width of 24” to cover the conveyor.  The model 110024 has a retail price of $491.00 each.  The cost of the drilled pipe was around $50.00.  What a difference in price!  But, how could EXAIR remain a leader in this industry for over 35 years?

Let’s continue on with the Return on Investment.  The amount of time required to install the Super Air Knife across the conveyor only took a maintenance staff about one hour to mount.  The labor rate that I will use in this example is $75.00 per hour (you can change this to your current labor rate).  The labor cost to install the knife is $75.00.   The Total Project Cost can be calculated as follows: ($491 – $50) + $75.00 = $516.00.  The next part of the equation, Total annual savings, is a bit more in-depth, but the calculation is shown below.

Super Air Knife

EXAIR manufactures engineered products to be efficient and safe.  The Super Air Knife has a 40:1 amplification ratio which means that 40 parts of “free” ambient air is entrained for every 1 part of compressed air.  For comparison, the Super Air Knives are to compressed air systems as LED lightbulbs are to electricity.  In that same way, the drilled pipe would represent an incandescent lightbulb.  The reason for this analogy is because of the amount of energy that the EXAIR Super Air Knives can save.  While LED lightbulbs are a bit more expensive than the incandescent lightbulbs, the value for the Return on Investment is at a higher percentage, or in other words, a short payback period.  On the other hand, the drilled pipe is less expensive to make, but the overall cost for using it in your compressed air system is much higher.  I will explain how below.

To calculate the Total Annual Savings, we will use the same blow-off scenario as above.  The amount of compressed air used by the drilled pipe is around 174 SCFM (4,924 SLPM) at 60 PSIG (4.1 Bar).  The model 110024 Super Air Knife has an air consumption of 55.2 SCFM (1,563 SLPM) at 60 PSIG (4.1 Bar).  At an electrical rate of $0.08 per Kilowatt-hour, we can figure the cost to make compressed air.   Based on 4 SCFM per horsepower of air compressor, the electrical cost is $0.25 per 1000 standard cubic feet, or $0.25/1000SCF.  To calculate an annual savings, let’s use a blow-off operation of 8 hours/day for 250 days a year.   Replacing the drilled pipe with the model 110024 Super Air Knife, it will save you (174 SCFM – 55.2 SCFM) = 121.8 SCFM of compressed air.  To put this into a monetary value, the annual savings will be 121.8 SCFM *$0.25/1000SCF * 60 Min/hr * 8hr/day * 250 day/yr = $3,654 per year.

With the Total Annual Cost and the Project Cost known, we can insert these values into Equation 1 to calculate the ROI:

ROI = (Total annual savings – Total Project Cost) / Project Cost * 100

ROI = ($3,654 – $516.00) / $516.00 * 100

ROI = 608%

With a percentage value that high, we are looking at a payback period of only 52 days.  You may look at the initial cost and be discouraged; but in a little over a month, the model 110024 will have paid for itself.  And after using it for one year, it will save your company $3,654.00.  Some things that may be overlooked are safety issues.  With some inexpensive blow-off devices, the noise levels are over the OSHA limits.  The drilled pipe had a noise level of 91 dBA while the Super Air Knife only had a noise level of 65 dBA.

In my experience, a loud blowing noise from your equipment is generally coming from an inefficient and safety-concerned product.  With these “cheap” ways to blow compressed air, it will cost your company a lot of money to use as shown in the example above.  If you would like to team up with EXAIR to set up ways to increase savings, improve productivity, and promote safety, an Application Engineer can help you to get started.

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