Line Loss: What It Means To Your Compressed Air Supply Pipe, Tubing, And Hose

“Leave the gun. Take the canolli.”

“What we’ve got here is failure to communicate.”

“I’ll get you my pretty, and your little dog too!”

“This EXAIR 42 inch Super Air Knife has ¼ NPT ports, but the Installation and Operation Instructions recommend feeding it with, at a minimum, a ¾ inch pipe…”

If you’re a movie buff like me, you probably recognize 75% of those quotes from famous movies. The OTHER one, dear reader, is from a production that strikes at the heart of this blog, and we’ll watch it soon enough. But first…

It is indeed a common question, especially with our Air Knives: if they have 1/4 NPT ports, why is such a large infeed supply pipe needed?  It all comes down to friction, which slows the velocity of the fluid all by itself, and also causes turbulence, which further hampers the flow.  This means you won’t have as much pressure at the end of the line as you do at the start, and the longer the line, the greater this drop will be.

This is from the Installation & Operation Guide that ships with your Super Air Knife. It’s also available from our PDF Library (registration required.)

If you want to do the math, here’s the empirical formula.  Like all good scientific work, it’s in metric units, so you may have to use some unit conversions, which I’ve put below, in blue (you’re welcome):

dp = 7.57 q1.85 L 104 / (d5 p)

where:

dp = pressure drop (kg/cm2) 1 kg/cm2=14.22psi

q = air volume flow at atmospheric conditions (FAD, or ‘free air delivery’) (m3/min) 1 m3/min = 35.31 CFM

L = length of pipe (m) 1m = 3.28ft

d = inside diameter of pipe (mm) 1mm = 0.039”

p = initial pressure – abs (kg/cm2) 1 kg/cm2=14.22psi

Let’s solve a problem:  What’s the pressure drop going to be from a header @80psig, through 10ft of 1″ pipe, feeding a Model 110084 84″ Aluminum Super Air Knife (243.6 SCFM compressed air consumption @80psig)…so…

q = 243.6 SCFM, or 6.9 m3/min

L = 10ft, or 3.0 m

d = 1″, or 25.6 mm

p = 80psig, or 94.7psia, or 6.7 kg/cm2

1.5 psi is a perfectly acceptable drop…but what if the pipe was actually 50 feet long?

Again, 1.5 psi isn’t bad at all.  8.2 psi, however, is going to be noticeable.  That’s why we’re going to recommend a 1-1/4″ pipe for this length (d=1.25″, or 32.1 mm):

I’m feeling much better now!  Oh, I said we were going to watch a movie earlier…here it is:

If you have questions about compressed air, we’re eager to hear them.   Call us.

Russ Bowman
Application Engineer
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Super Air Knife is Most Efficent in Compressed Air Usage

 Of the 3 styles of Air Knife offered by EXAIR, the Super, Standard and Full-Flow, the Super Air Knife is our most efficient, in regards to compressed air usage. Using a 40:1 amplification rate of entrained ambient air to compressed air consumed, it uses only 2.9 SCFM per inch of knife length when operated at 80 PSIG, while producing a low sound level of only 69 decibels (the quietest on the market today). The Super Air Knife provides  an even laminar flow of air across the length of the knife and is available in single piece lengths from 3″ up to 108″ in aluminum, 303 stainless and 316 stainless as well as up  to 54″ in PVDF (Polyvinylidene Flouride) construction for applications where aggressive chemicals may be present. 1/4″ FNPT air inlets are available on each end as well as on the bottom of the knife.

Aluminum, Stainless Steel and PVDF Super Air Knives

For Super Air Knives 24″ and longer, you need to plumb air to multiple inlets to maintain an even airflow. Our available Plumbing Kits includes the properly sized hose or pipe and fittings, to not only save valuable time looking for these parts yourself but also eliminates the potential of using undersized lines which will reduce the performance of the Super Air Knives.

For Super Air Knives in aluminum construction, the Plumbing Kits include cut to length PVC compressed air hose and the required brass fittings.

Plumbing Kit for aluminum Super Air Knives

The Plumbing Kits for our stainless steel and PVDF Super Air Knives, include 316ss cut to length pipe as well as 316ss fittings.

Plumbing Kit for 303ss, 316ss and PVDF Super Air Knives

The Super Air Knife is the ideal choice when looking to treat wide-area applications, like cleaning a conveyor or drying parts after a wash process. For help selecting the best product to fit your process, contact one of our application engineers for assistance.

Justin Nicholl
Application Engineer
justinnicholl@exair.com
@EXAIR_JN

 

Troubleshooting Vortex Tube Performance

image-2
This Vortex Tube was not operating properly when initially connected to compressed air

One of the fun parts of Application Engineering at EXAIR is explaining the operation of Vortex Tubes to our customers.  Sometimes they’re described as a “reverse tornado” inside of a tube, spinning a pressurized airstream and converting it into a hot and cold flow.  Other times we describe it through the generation of two vortices with differing diameters, and the difference in diameters results in one vortex shedding energy in the form of heat.

But, no matter the way we explain their operation, we always stress the importance of proper compressed air plumbing.  If the compressed air piping/hoses/connections are not properly sized, performance problems can arise.  (This is true for any compressed air driven device.)

This fundamental came to light when working with one of our customers recently.  They were using a medium sized Vortex Tube to provide spot cooling in an enclosed space, but were not seeing the flow and temperature drop they knew to be possible with an EXAIR Vortex Tube.  And, after looking at installation photos of the application, the root cause was quickly spotted.

image-2-with-arrow
The red arrow in the bottom right corner of this image shows the beginnings of a reduction in compressed air supply.

I noticed what looked to be a very small hose connected to the inlet of the Vortex Tube in the image above.

image-1-with-circle
In this additional image, the small compressed air line is in full view. This was the root cause for performance problems in this application.

After further inspection of another photo, the small diameter tube was in full view.  This small hose serves as a restriction to compressed air flow, which in turn limits both flow and operating pressure of the downstream devices.  What that meant for this application, was poor performance from the Vortex Tube, all stemming from this reduction in piping size.

When looking to find the root cause of a performance issue with a compressed air driven unit, things aren’t always as easy as they were with this application.  A visual inspection is always a good idea, but if everything looks correct, here is a list of troubleshooting steps to consider:

  1. Check for quick-disconnects in the plumbing system.  Quick-disconnects are great from an operator’s perspective, but they can wreak havoc on compressed air flows due to small inside diameters and air volume restriction.
  2. Determine the operating pressure at the device.  This is imperative.  In order to make proper decisions to correct the performance concern, good information is required.  Knowing what is happening at the device is crucial for proper understanding.  There may be 100 PSIG at the main compressed air line, but only 60 PSIG at the device due to plumbing problems. A pressure gauge at the inlet of the compressed air product can provide this information.
  3. Check that the compressed air system has enough volume to properly supply the device.  A compressed air driven unit without the correct volume of compressed air is just as bad as having a lack of pressure.
  4. Check for leaks.  The US Department of Energy estimates that 20-30% of compressor output in industrial facilities is lost as leaks.  If your system and devices aren’t operating as they’re supposed to, check for leaks.  They may be contributing to the poor performance.  (Don’t know where your leaks are coming from?  Use our Ultrasonic Leak Detector!)

Fortunately for this customer, after improving the size of this tubing performance was on par with our published specifications and this customer was back in operation.  If you have a question about how to improve the utilization of the compressed air devices in your application, contact an EXAIR Application Engineer.

Lee Evans
Application Engineer
LeeEvans@EXAIR.com
@EXAIR_LE