How to Calculate and Avoid Compressed Air Pressure Drop in Systems

EXAIR has been manufacturing Intelligent Compressed Air Products since 1983.  They are engineered with the highest of quality, efficiency, safety, and effectiveness in mind.  Since compressed air is the source for operation, the limitations can be defined by its supply.  With EXAIR products and pneumatic equipment, you will need a way to transfer the compressed air from the air compressor.  There are three main ways; pipes, hoses and tubes.  In this blog, I will compare the difference between compressed air hoses and compressed air tubes.

The basic difference between a compressed air hose and a compressed air tube is the way the diameter is defined.    A hose is measured by the inner diameter while a tube is measured by the outer diameter.  As an example, a 3/8” compressed air hose has an inner diameter of 3/8”.  While a 3/8” compressed air tube has an outer diameter that measures 3/8”.  Thus, for the same dimensional reference, the inner diameter for the tube will be smaller than the hose.

Why do I bring this up?  Pressure drop…  Pressure Drop is a waste of energy, and it reduces the ability of your compressed air system to do work.  To reduce waste, we need to reduce pressure drop.  If we look at the equation for pressure drop, DP, we can find the factors that play an important role.  Equation 1 shows a reference equation for pressure drop.

Equation 1:

DP = Sx * f * Q1.85 * L / (ID5 * P)

DP – Pressure Drop

Sx – Scalar value

f – friction factor

Q – Flow at standard conditions

L – Length of pipe

ID – Inside Diameter

P – Absolute Pressure

 

From Equation 1, differential pressure is controlled by the friction of the wall surface, the flow of compressed air, the length of the pipe, the diameter of the pipe, and the inlet pressure.  As you can see, the pressure drop, DP, is inversely affected by the inner diameter to the fifth power.  So, if the inner diameter of the pipe is twice as small, the pressure drop will increase by 25, or 32 times.

Let’s revisit the 3/8” hose and 3/8” tube.  The 3/8” hose has an inner diameter of 0.375”, and the 3/8” tube has an inner diameter of 0.25”.  In keeping the same variables except for the diameter, we can make a pressure drop comparison.  In Equation 2, I will use DPt and DPh for the pressure drop within the tube and hose respectively.

Equation 2:

DPt / DPh = (Dh)5 / (Dt)5

DPt – Pressure drop of tube

DPh – Pressure Drop of hose

Dh – Inner Diameter of hose

Dt – Inner Diameter of tube

Thus, DPt / DPh = (0.375”)5 / (0.25”)5 = 7.6

As you can see, by using a 3/8” tube in the process instead of the 3/8” hose, the pressure drop will be 7.6 times higher.

Diameters: 3/8″ Pipe vs. 3/8″ tube

At EXAIR, we want to make sure that our customers are able to get the most from our products.  To do this, we need to properly size the compressed air lines.  Within our installation sheets for our Super Air Knives, we recommend the infeed pipe sizes for each air knife at different lengths.

There is also an excerpt about replacing schedule 40 pipe with a compressed air hose.  We state; “If compressed air hose is used, always go one size larger than the recommended pipe size due to the smaller I.D. of hose”.  Here is the reason.  The 1/4” NPT Schedule 40 pipe has an inner diameter of 0.364” (9.2mm).  Since the 3/8” compressed air hose has an inner diameter of 0.375” (9.5mm), the diameter will not create any additional pressure drop.  Some industrial facilities like to use compressed air tubing instead of hoses.  This is fine as long as the inner diameters match appropriately with the recommended pipe in the installation sheets.  Then you can reduce any waste from pressure drop and get the most from the EXAIR products.

With the diameter being such a significant role in creating pressure drop, it is very important to understand the type of connections to your pneumatic devices; i.e. hoses, pipes, or tubes.  In most cases, this is the reason for pneumatic products to underperform, as well as wasting energy within your compressed air system.  If you would like to discuss further the ways to save energy and reduce pressure drop, an Application Engineer at EXAIR will be happy to assist you.

 

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

EXAIR Hoses and Tubes are Great Accessories

EXAIR offers different styles of hoses and tubes as accessories to our product lines.  They are built and designed to easily fit with our products as well as being sized correctly to not affect performance.  It simplifies the use, setup, and integration of EXAIR products in your facility.   You do not have to determine the proper diameters, pressure ratings, or end fittings to best fit the EXAIR products to maximize their performance.  Also, having these items available from one source minimizes the number of purchases and vendors necessary for a complete and working solution. In this article, I will go over the different hoses and tubes that EXAIR can provide.

Conveying Hoses:

The hoses above are used with our Air Operated Conveyors or Line Vacs.  The Line Vacs are designed to move product from point A to point B.  If the Line Vac is the “vehicle”, the Conveyance Hose is the track.  The hoses are made of a durable PVC semi-flexible hose with 6 different diameters from ¾” I.D. to 3” I.D.  The conveyance hose can slip easily onto the EXAIR non-threaded style of Line Vacs.  EXAIR can cut-to-length Conveying Hoses up to 50 feet (15m); in increments of 10 feet (3m).

Coiled Hoses:

To get compressed air from the piping system to the Safety Air Guns, we offer a series of Coiled Hoses.  They are made of a durable abrasion-resistant nylon material that is 12 feet long (3.6 meters).  They have swivel fittings to allow for easy uncoiling, and a spring strain relief to keep the hose from kinking.  The coiled design makes it easy to reach around the work area and retract back to the substation.  This will help to keep the hose off the ground where potential dangers could occur.  We offer 3 different connection sizes of 1/8” NPT, ¼” NPT, and 3/8” NPT to attach right to the Safety Air Guns.  With the proper size, the Coiled Hoses can supply the required amount of compressed air with a minimal amount of pressure drop.

Compressed Air Hoses:

If you need a compressed air line to reach from overhead or around equipment, the EXAIR Compressed Air Hoses would work with these applications.  They are made from a reinforced synthetic rubber in 3/8” I.D. and 1/2” I.D. diameters.  We can make specific lengths up to 50 feet (15m).  They are rated for 250 PSIG (17 bar) air pressure, and the hose material works well for long lasting protection against ozone, weathering and temperatures up to 158oF (70oC).  They come with two male ends in ¼” NPT or ½” NPT.

Stay Set Hoses:

The Stay Set Hose gives you that possibility of manually adjusting or re-adjusting Super Air Nozzles.  The hose has a “memory” function, and it will not creep or droop until you physically move it.  They work well to direct air flows in specific target areas.  They can be used with Super Air Nozzles, Safety Air Guns and Blow-off Kits.  The Stay Set Hoses come in lengths from 6” (15cm) to 36” (91cm), and they are offered with ¼” NPT male on both ends or with a 1/8” NPT female and a ¼” NPT male connections.  These hoses are rated for 250 PSIG (17 bar) and are made from reinforced synthetic rubber.  If positioning is required for accurate blowing or re positioning for different areas, the Stay Set Hose would be a nice addition to your equipment.

Vacuum Tubing:

For our E-Vac product line, EXAIR offers vacuum hoses to connect the E-Vac vacuum generators to the suction cups.  They are made from polyurethane in ¼” O.D. and 3/8” O.D.  The tubing is very flexible for moving product, and they can resist the vacuum pressures created by the E-Vac.  They slip easily into our Push-In Connectors to quickly attach vacuum cups to the E-Vac system.  EXAIR can sell both types of tubing up to 50 feet (15m) in increments of 10 feet (3m).

Hoses and tubes may seem like simple things, but EXAIR already did all the research in determining the best material and correct size for optimum performance.  You can leverage this information to save you time and money when using EXAIR products in your application.  If you need help in selecting the correct model, you can contact an Application Engineer.  We will be happy to help you.

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

The (Not So) Dreaded Warranty Claim Call

If you’ve ever worked in customer service or technical support, it’s almost a foregone conclusion that you’ve spoken with someone who isn’t getting what they wanted from your products and/or services. And no matter who you are, you’ve almost certainly spoken with someone you’ve bought something from, because you’re not getting what you wanted from it, right? And we can all (I hope) agree that there are MANY things we’d rather do than make…or receive…those calls.

I had the pleasure of assisting a customer yesterday who wasn’t getting what he wanted from an EXAIR product: in this case, it was one of our Stay Set Hoses. It seems that the bendable element inside had broken, meaning the Stay Set Hose was no longer “staying set.”  Since this unit had only been in service for about a month, I was anxious to know what would cause such a failure on a solid product with such a successful track record.  The caller was up front, early in the conversation, with his understanding that we can’t warranty against everything that a user might do to our products (the fact of the matter is, we do honor a 5 year “Built To Last” warranty against manufacturing defects,) and we shared a quick laugh because we both remembered this luggage commercial:

By this time, it was the best warranty claim conversation ever.

Flexible and durable, EXAIR Stay Set Hoses come in lengths from 6" to 36".
Flexible and durable, EXAIR Stay Set Hoses come in lengths from 6″ to 36″.

This particular Stay Set Hose was one of many in their plant, so we had a good discussion of some common best practices for their use:

*Keep bends as gradual as possible, especially if repositioning is frequent.

*Use two hands to bend the hose, as much as possible, to prevent/limit an excessive amount of leveraged force being applied to the connecting end of the bending element.

*When re-positioning is needed, do not grab onto the point of use device (Air Nozzle, Air Amplifier), but instead, use the spring relief as a grip to bend the blow off device into place.

*Keep in mind they’re PVC…temperature rating is 158°F. They’ll handle a fair amount of heat, but take advantage of their flexibility and bend them well away from any hot surfaces.

Like I said, this hose had only been in service for about a month, so we’re getting it back in the shop for failure analysis. Stay tuned for a future installment, where I’ll tell you how the rest of EXAIR’s warranty evaluation process works.

Russ Bowman
Application Engineer
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