Issues and Problems with Pressure Drop

 

Super Air Knife Install Sheet

Pressure drop comes in different forms, and it causes inefficiencies within your pneumatic system.  EXAIR writes statements in the installation manuals to help find the correct pipe sizes to supply the different products.  (Reference Super Air Knife Installation Manual above).   But there are other areas that can affect the performance.  These can be fittings, tubing, valves, and accessories.  In this blog, I will cover some pitfalls that can minimize the potential of your EXAIR products.

Pressure drop by definition is a difference or loss in pressure.  A properly sized Filter Separator will typically have a pressure drop of 5 PSID (0.3 bar) at the rated conditions.  So, if you start with 100 PSIG (6.9 bar), the air pressure after the filter separator will be 95 PSIG (6.6 bar).  But what happens when a filter separator is undersized or too small?  The pressure drop will be much higher.  So, if the pressure drop is 30 PSID (2 bar), then the downstream air pressure will only be 70 PSIG (4.8 bar).  At that pressure, you may not be able to get the performance that is required to do the job.

The first thing in determining these potential issues is what I like to call forensics.  If you can install a pressure gage at the inlet of any EXAIR product, then you can deduce if a potential problem is within your setup.   For example, if the Pressure Regulator is at 100 PSIG (6.9 bar), and the pressure gauge at the inlet is reading only 60 PSIG (4.1 bar), then there is a pressure drop of 40 PSID (2.8 bar) between these two points.  You can look in this area for the problem or problems.  If the gauge on the Pressure Regulator goes down as well when you are operating, then the problem area is upstream of the Pressure Regulator.  This can be from the pipe size or the air compressor.

The most common issues are fittings and tubing.  With fittings, small openings may not allow enough air to pass through.  Above is a photo of some typical fittings.  You notice that the right side of the chart has large enough openings to decrease pressure drop.  In some instances, quick connect fittings are commonly used to easily connect or disconnect pneumatic devices; but if you use too small or too many of these fittings, they can cause a large pressure drop.

The other problem is with the inner diameter of tubing, hoses, or pipes that are not properly sized.  Russ Bowman, a colleague, created a video showing the issues with improperly sized plumbing.  It is a very interesting video that shows the effect on a Super Air Knife.

If you want to get the most from your EXAIR products, you will need to reduce the amount of pressure drop in your system.  Pressure drop is wasted energy and can affect your pneumatic system.  You can follow my recommendations above.  Or if you would like to discuss your setup with an Application Engineer, we will be happy to assist.

John Ball
Application Engineer

Email: johnball@exair.com
Twitter: @EXAIR_jb

Rotary Scroll Compressors

Over the years, my EXAIR colleagues and I have blogged about different types of air compressor types including single and double acting reciprocating, rotary screw and sliding vane air compressors. You can click on the links above to check those out. Today, I will review the basics of the rotary scroll-type compressor.

The rotary scroll type compressor falls under the positive displacement-type, the same as the other types previously discussed.  A positive displacement type operates under the premise that a given quantity of air is taken in, trapped in a compression chamber and the physical space of the chamber is mechanically reduced.  When a given amount of air occupies a smaller volume, the pressure of the air increases.

Positive displacement type compressors

Each of the previous positive displacement type compressors use a different mechanism for the reduction in size of the compression chamber. The rotary scroll uses two inter-meshing scrolls, that are spiral in shape. One of the scrolls is fixed, and does not move (red).  The other scroll (black) has an “orbit” type of motion, relative to the fixed scroll. Air would be drawn in from the left, and as it flows clockwise through the scroll, the area is reduced until the air is discharged at a high pressure at the center.

How it Works

There is no metal to metal sliding contact, so lubrication is not needed.  A drawback to an oil free operation is that oil lubrication tends to reduce the heat of compression and without it, the efficiency of scroll compressors is less than that of lubricated types.

The advantages of the rotary scroll type compressor include:

  • Comes as a complete package
  • Comparatively efficient operation
  • Can be lubricant-free
  • Quiet operation
  • Air cooled

The main disadvantage:

  • A limited range of capacities is available, with low output flows

EXAIR recommends consulting with a reputable air compressor dealer in your area, to fully review all of the parameters associated with the selection and installation of a compressed air system.

If you would like to talk about compressed air or any of the EXAIR Intelligent Compressed Air® Products, feel free to contact EXAIR and myself or one of our Application Engineers can help you determine the best solution.

Jordan Shouse
Application Engineer

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Rotary Scroll GIF:  used from  Public Domain
Images Courtesy of  Compressor1 Creative Commons.

 

Super Air Knife’s Adjustability and Flexibility = Success

The EXAIR Super Air Knife is the most efficient compressed air knife on the market. We know this because we’ve tested them, and our competitors’ offerings, for performance, using the same instruments, controls, and procedures. We’re not going to publish data that we can’t back up, and that’s a fact.

48insak_pr
EXAIR Super Air Knife removing moisture after a rinse on anodized parts.

They’re also ideally suited to a wide variety of applications – they come in lengths from 3 inches to 9 feet long (and can actually be coupled together for uninterrupted air flows of even longer lengths,) a variety of materials for just about any environment. But the best thing about our Super Air Knives is how you can adjust the air pressure and flow to complete a wide variety of tasks. You can adjust them in two different ways, Replacing or adding Shims, or regulating the incoming air pressure.

completeAirknifesets
Shims for the aluminum, 303 Stainless Steel, and 316 Stainless Steel Super Air Knives

Changing out your shim!

A larger shim gap will give you higher flow and force from your Air Knife. Honestly, the 0.002″ shim that comes pre-installed in all of our Air Knives is perfectly suitable for most blow off applications, and appropriate air supply conditions are the first thing you should check for before going with thicker shims, but if you do indeed need a boost, a thicker shim will indeed give you one…here’s a blog with the video to show you how it’s done:

How_to_change_air_knife_shim
Video Blog: How to Change a Shim in a Super Air Knife

Filter Regulator
Regulator and filter

Another advantage to having a Pressure Regulator at every point of use is the flexibility of making pressure adjustments to quickly change to varying production requirements.  Not every application will require a strong blast sometimes a gentle breeze will accomplish the task.  As an example one user of the EXAIR Super Air Knife employs it as an air curtain to prevent product contamination (strong blast) and another to dry different size parts (gentle breeze) coming down their conveyor. For Performance at different supply pressures see the chart below.

Super_Air_Knife_Performance
Super Air Knife Performance Table

EXAIR products are highly engineered and are so efficient that they can be operated at lower pressures and still provide exceptional performance!  This save’s you money considering compressed air on the average cost’s .25 cents per 1000 SCFM.

If you’d like to discuss altering the performance of your Super Air Knife, give us a call.

Jordan Shouse
Application Engineer
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The Bernoulli Principle

What do baseball, airplanes, and your favorite singer have in common? If you guessed that it has something to do with the title of this blog, dear reader, you are correct.  We’ll unpack all that, but first, let’s talk about this Bernoulli guy:

Jacob Bernoulli was a prominent mathematician in the late 17th century.  We can blame calculus on him to some degree; he worked closely with Gottfried Wilhelm Leibniz who (despite vicious accusations of plagiarism from Isaac Newton) appears to have developed the same mathematical methods independently from the more famous Newton.  He also developed the mathematical constant e (base of the natural logarithm) and a law of large numbers which was foundational to the field of statistics, especially probability theory.  But he’s not the Bernoulli we’re talking about.

Johann Bernoulli was Jacob’s younger brother.  He shared his brother’s passion for the advancement of calculus, and was among the first to demonstrate practical applications in various fields.  So for engineers especially, he can share the blame for calculus with his brother.  But he’s not the Bernoulli we’re talking about either.

Johann’s son, Daniel, clearly got his father’s math smarts as well as his enthusiasm for practical applications, especially in the field of fluid mechanics.  His kinetic theory of gases is widely known as the textbook (literally) explanation of Boyle’s law.  And the principle that bears his name (yes, THIS is the Bernoulli we’re talking about) is central to our understanding of curveballs, airplane wings, and vocal range.

Bernoulli’s Principle states that an increase in the speed of a fluid occurs simultaneously with a decrease in pressure (e.g., the fluid’s potential energy.)

  • In baseball, pitchers love it, and batters hate it.  When the ball is thrown, friction (mainly from the particular stitched pattern of a baseball) causes a thin layer of air to surround the ball, and the spin that a skilled pitcher puts on it creates higher air pressure on one side and lower air pressure on the other.  According to Bernoulli, that increases the air speed on the lower pressure side, and the baseball moves in that direction.  Since a well-thrown curveball’s axis of rotation is parallel to the ground, that means the ball drops as it approaches the plate, leaving the batter swinging above it, or awkwardly trying to “dig it out” of the plate.
  • The particular shape of an airplane wing (flat on the bottom, curved on the top) means that when the wing (along with the rest of the plane) is in motion, the air travelling over the curved top has to move faster than the air moving under the flat bottom.  This means the air pressure is lower on top, allowing the wing (again, along with the rest of the plane) to rise.
  • The anatomy inside your neck that facilitates speech is often called a voice box or vocal chords.  It’s actually a set of folds of tissue that vibrate and make sound when air (being expelled by the lungs when your diaphragm contracts) passes through.  When you sing different notes, you’re actually manipulating the area of air passage.  If you narrow that area, the air speed increases, making the pressure drop, skewing the shape of those folds so that they vibrate at a higher frequency, creating the high notes.  Opening up that area lowers the air speed, and the resultant increase in pressure lowers the vocal folds’ vibration frequency, making the low notes.
  • Bonus (because I work for EXAIR) Bernoulli’s Principle application: many EXAIR Intelligent Compressed Air Products are engineered to take advantage of this phenomenon to optimize efficiency:

The high speed of the air exiting the (left to right) the Air Wipe, Super Air Knife, Super Air Nozzle, and Air Amplifier creates a low pressure (just like Daniel Bernoulli said) that causes entrainment of an enormous amount of air from the surrounding environment.  This maximizes flow while minimizing consumption of your compressed air.

If you’d like to discuss Bernoulli, baseball, singing, or a potential compressed air application, give me a call.  If you want to talk airplane stuff, perhaps one of the other Application Engineers can help…I don’t really like to fly, but that’s a subject for another blog.

Russ Bowman
Application Engineer
EXAIR Corporation
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