Importance Of Proper Pneumatic Tube, Pipe, And Fittings

When it comes to engineered compressed products, the number one cause of less-than-optimal performance is improper supply line sizing.  This can mean one of two things:

  • The hose, pipe, or tubing running to the device is too small in diameter.
  • The hose, pipe or tubing is big enough in diameter, but too long.

The problem with either of these is line loss (follow that link if you want to do the math.)  Put simply, the air wants to move faster than it’s physically permitted to.  Any time fluid flows through a conduit of any sort, friction acts on it via contact with the inside surface of said conduit.

With smaller diameters, a larger percentage of the air flow is affected…no matter what diameter the line is, the air closest to the inner wall is affected by the friction generated.  When diameter increases, the thickness of this affected zone doesn’t increase proportionally, so larger diameters mean less of the air is affected by friction.  It also means there’s a lot more room (by a factor of the square of the radius, times pi…thanks, Archimedes!) for the air to flow through.

Likewise, with longer lengths, there’s more contact, which equals more friction.  Length, however, is often a non-negotiable.  You can’t just up and move a 100HP air compressor from one part of the plant to another.  So, when we’re talking about selecting proper supply lines, we’re going to start with the distance from the compressed air header to our device, and pick the diameter that will give us the flow we need through that length.  In fact, that’s exactly how to use the Recommended Infeed Pipe Size table in EXAIR’s Super Air Knife Installation & Maintenance Guide:

This table comes directly from the Installation & Operation Instructions for the Super Air Knife.

Once we have the correct line size (diameter,) let’s consider the fittings:

  • Tapered pipe threads (NPT or BSPT) are the best.  They offer no restriction in flow, and are readily commercially available.  If you’re using pipe, these are the standard threads for fittings.  If you want to use hose, a local hydraulic/pneumatic shop can usually make hoses with the fittings you need, at the service counter, while you wait.
  • If you need to frequently break and make the connection (e.g., a Chip Vac System that’s used throughout your facility,) quick connects are convenient and inexpensive.  Push-to-connect types are by far the most common, but a word of warning: they’re notoriously restrictive, as the inside diameter of the male end is markedly smaller than the line size.  If you use them, go up a size or two…a quick connect made for 1/2 NPT connections will work just fine for a 1/4″ line:
  • The nice thing about these quick connects is that you don’t have to depressurize the line to make or break the connection.  If you have the ability to depressurize the line, though, claw-type fittings (like the one shown on the right) provide the convenience of a quick connect, without the restriction in flow.

Proper air supply is key to performance of any compressed air product.  If you want to know, at a glance, if you’re supplying it properly, install a pressure gauge right at (or as close as practical) to the inlet.  Any difference in its reading and your header pressure indicates a restriction.  Here’s a video that clearly shows how this all works:

I want to make sure you get the most out of your compressed air system.  If you want that to, give me a call with any questions you might have.

Russ Bowman
Application Engineer
EXAIR Corporation
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Video Blog: Super Air Knife with Plumbing Kit Installed

 

This short video features our new Stainless Steel Plumbing kits. Ordering a Super Air Knife with the Plumbing Kit installed, provides the best performance and makes for an easy installation.

 

 

Please contact an application engineer for assistance @ 800-903-9247.

Justin Nicholl
Application Engineer
justinnicholl@exair.com
@EXAIR_JN

Engineered Solutions Are Cost Effective

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One of the easiest ways to solve a blow off application is to install an open pipe or tube; it’s generally quick and available. They are easy to make, mainly you just need some pipe, maybe a hacksaw and hammer, and a way to hook them up to your compressed air system.  They will provide a good amount of force but at the cost of safety, noise level, and air consumption. That’s right: it will cost you in SAFETY, NOISE EXPOSURE and COMPRESSED AIR CONSUMPTION. I’m going to go out on a limb here (not really) and wager there are a number of folks in any organization unwilling to pay those costs – if you are willing, you may want to reconsider.

I have been to many manufacturing facilities where they have used copper line to bend into a tight space and then pump 85 psi into the pipe in order to try and blow a piece of lint out of a roller or to keep trim from getting caught in a pulley system.  In some cases I have seen 3/8″ ID pipe to keep dust and lint out of a pulley.

This is not needed at all.   The estimated flow through a 3/8″ ID tube that is around 3′ long would be roughly 109 SCFM when powered at 85 psig.   All to keep dust off and loose fiber out of a certain area.  The reason they plumbed this large of a piece of tubing into the area was simple, it’s what they had and it worked great (words from the maintenance worker). For additional reference, our 91 SCFM air nozzle produces 4.5 pounds of force which seems a bit of overkill when you can blow dust away with your breath.

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In one instance I looked over the material and scrap they were trying to keep from getting to the outer workings of the machine I made the recommendation for them to utilize a model 1100SSW, –  a 1/4 NPT Stainless Steel Super Air Nozzle w/ Swivel Fitting.   This would give them flexibility to target the right area through the swivel and require them to change the existing tubing out to a schedule 40 threaded pipe, or use a compression style fitting.

By replacing the single nozzle, the customer was able to reduce compressed air consumption in just this single blow off point from 109 SCFM at 85 psig to 14 SCFM at 80 psig inlet pressure.  This single replacement equates to saving 95 SCFM, or $11.40 per 8 hour shift that the blowoff is operated.   If the customer operated this blowoff 24 hours a day it would take a mere 4 days to pay the unit back in air savings.

The above savings do not include the benefit of being able to reduce the overall operating pressure of the compressed air system feeding this application to 80 psig, instead of 85 psig. In case you weren’t aware, if you lower the pressure value where your compressor shuts off, say from 85 psig to 80 psig, it will save an estimated 2.5% of drive energy for their air compressor.   Depending on the type and size of the compressor this could amount to a substantial savings.  This system pressure reduction will also lower the operating pressure of any leaks that may be within the system which will also be another amount of savings.  All of this is from simply replacing open pipe with an engineered nozzle.

This was just one area where the quick and easy way turned out to be the costly and dangerous path.  The best part about our engineered solution is they are all in stock, ready to ship same day.  This means you can find the problem today, have a solution waiting to be installed tomorrow.

Brian Farno
Application Engineer
BrianFarno@EXAIR.com
@EXAIR_BF

Dude, Where’s My Air Pressure?

The question comes up every so often. “I have 10 BARG plant pressure, but can only get 2 BARG pressure on the gauge at your Chip Vac.  What is the problem?”

We call the problem “pressure drop”. And pressure drop is attributed to many things. All of them have to do with the delivery of the compressed air supply up to the point of use or product.  In this case, the product was EXAIR’s 5 Gallon Chip Vac Model 6193-5. We found that actually having a pressure gauge installed right at the inlet of the Chip Vac vacuum generating part itself help greatly for the customer to realize the nature of their problem. The sources of such problems are usually to do with the diameter of the compressed air line feeding the “device” being too small. You will probably note in the photo that the customer has installed a 6 mm inside diameter line with a quick connect fitting. Upon further questioning of the customer, this supply line was 10 meters (33 ft) long. The Chip Vac requires 33 SCFM @ 80 PSIG (934 SCFM @ 5.5 BARG) to operate as advertised. Note this is the requirement at the inlet. Where you measure pressure in a compressed air system is of utmost importance. And for any compressed air consuming device, that value is going to be as used at the inlet, not at the wall or wherever the compressed air drop may be located.

Once the customer was able to increase to a 12 mm ID line and cut the length down to about 5 meters, the Chip Vac performed as intended. This was because it was no longer starving for compressed air through the smaller line.

We notice that many customers will try to get away with using too small a diameter of compressed air line. Perhaps it is what they had on hand or it was cheap to get. The problem is they end up shooting themselves in the foot when it comes to performance of the product connected out at the point of use.

By taking the time to practice proper plumbing technique, one can save themselves a lot of headache when setting up any pneumatic equipment. Of course, if you need advice on what the proper line size needs to be for any given installation, give us a call. We’ll be glad to assist you.

Neal Raker, Application Engineer
nealraker@exair.com