Proper Plumbing Means Proper Performance

36″ Aluminum Super Air Knife being used in a monofilament extrusion line

An EXAIR customer recently contacted me about the application shown above, using an aluminum Super Air Knife model 110036 as a component to a blow off application in a monofilament extrusion line.  The extrusions from this line are used in one of the end user’s main product lines, a personal health device used by over a billion people around the world.

The original problem of drying the extrusions can certainly be solved with the setup shown, but the output force from the knife was less than what the customer expected, and below the EXAIR published data.  We take great care in the collection and verification of our performance data, so this prompted a deeper dive into the application to determine what could be the cause.

Immediately upon seeing the application photos, there were two things which stood out.  The first was the angle of attack of the knife, and the second was the compressed air plumbing.  The angle of attack in the original setup was ~90°, nearly perpendicular to the extrusions passing through the airstream from the knife.  EXAIR always recommends an angle of attack of ~45° to increase time in contact between the airstream from the knife and the materials passing through the airstream.  Although a small adjustment, this angle significantly contributes to overall blow off performance.

5mm ID x 8mm OD tubing used to supply compressed air to the knife

But, the real issue with this application was in the compressed air supply.  The tubing for this knife was shown as having a 5mm ID and an 8mm OD, which will allow a compressed air flow of ~40 SCFM at 80 PSIG, maximum, without consideration to pipe length from the compressor.  The 36” aluminum Super Air Knife will require 104.4 SCFM at 80 PSIG operating pressure.  So, it was clear that there was a significant plumbing problem, leading to the reduced performance from the knife.

In order to prove this out, we first had to take a pressure reading directly at the knife.  When this was done, the operating pressure dropped from ~85 PSIG at the main header to less than 20 PSIG at the knife.  By taking this pressure reading directly at the knife we were able to gain valuable information as to the true operating pressure of the knife, which was far below what the customer expected, but which made perfect sense given the performance output.

The remedy in this case was to increase the size of the supply line to at least 15mm ID (approximately equivalent to a ½” schedule 40 line), and preferably to something in the range of 19-20mm (~a ¾” schedule 40 line).  Once this was done the knife operated flawlessly, and after adjusting the angle of attack this application was optimized for the best possible results.

Being able to find the source of the problem for this application was a great service to the customer.  Our engineers are well-versed in compressed air system requirements, and we’re available for help in your application if needed.  If you’d like to contact an EXAIR Application Engineer we can be reached by email, phone (1-800-903-9247), or Twitter.

Lee Evans
Application Engineer
LeeEvans@EXAIR.com
@EXAIR_LE

Proper Air Supply Is Key To Optimal Performance

I recently worked with a customer who was using our 36″ aluminum Super Air Knife to remove dust and light debris from a conveyor but wasn’t seeing good performance. They initially called because they read in their catalog that increasing the shim gap would increase their force and flow and wanted to know what kind of increase in performance they would see.

The Super Air Knives are shipped from EXAIR with a .002″ shim installed and the performance data shown in the catalog reflects this gap setting. The shim sets, for aluminum knives, include a .001″, .003″ and .004″ shim and by changing to the .003″ shim, the force and flow would be 1.5 times as great and using the .004″ shim would double these amounts. While some applications do require the additional force and flow, trying to blow off dust or light materials typically wouldn’t fall into this category.

sak-shims

Replaceable shims provide varying levels of force and flow.

Switching our focus to the supply side of things, it turns out they were using 1/4″ hose and only plumbing one end of the unit. This poses 2 concerns that relate directly to the mentioned poor performance. The first would be the 1/4″ hose is severely undersized for a 36″ Super Air Knife. We recommend 3/4″ Schedule 40 pipe if the length of supply from a main header is 10′ or less and a 1″ pipe up to 50′ of supply run. It is possible to use hose but that hose needs to be at least 1″ ID to be able to carry enough volume to support a 36″ unit. Secondly, for knives that are 24″ in length or longer, you need to plumb air to both ends to maintain an even, laminar flow across the length of the knife.

With the proper supply, the Super Air Knife is going to produce an exhaust air velocity of 11,800 feet per minute when operated at 80 PSIG, which is more than enough to eject lightweight material from a flat surface (in fact you could most likely clean dust and light debris at a lower pressure). If the customer did increase the shim gap dimension, the increase in  air demand would only worsen the problem of undersized supply lines.

Pipe sizes

Recommended supply line sizes per the IOM – Installation and Operation Manual.

This is just one example of how proper supply line size and installation is key to achieving optimal performance. If you are experiencing similar issues or need any assistance with a product or application, give me a call, I am glad to help.

Justin Nicholl
Application Engineer
justinnicholl@exair.com
@EXAIR_JN

 

 

Typical Compressed Air Plumbing Mistakes

As a manufacturer of Intelligent Compressed Air Products, we like to address one of the most common problems with installation, proper plumbing.  A picture is worth a 1,000 words, and knowledge is power.  I will show both to help eliminate any pitfalls when installing our products.

A customer purchased a model 110072 Super Air Knife.  It is a powerful and efficient air knife that is 72 inches (1.8 meter) long.  He mounted it across his sheet to blow debris off from the surface of his product.  After installing the Super Air Knife, he was having issues in getting a strong even force along the entire knife.  He would only get compressed air blowing on the ends of the Super Air Knife.  The center did not have anything coming out.  He needed our help to solve.  In detailing my forensics, I asked him for pictures of his installation as I went over some basic questions.  Here is what we found:

Question 1: What is the pressure at the entrance of the Super Air Knife?

Answer 1: 95 psig (6.5 bar)

Picture: The gage reading is at the regulator.

Solution: There should also be a pressure gage right at the entrance of the Super Air Knife. It helps to define any issues in the system by comparing line pressure at the regulator to inlet pressure at the Super Air Knife.  This customer would see a very low air pressure at the Super Air Knife caused by all the restrictions (reference below).

Issue 1

Issue 1

Question 2: What size is your compressed air line that is supplying the Super Air Knife?

Answer 2: 1 ½” NPT pipe. (From the installation manual, this is the correct size pipe to supply the air required for the Super Air Knife when it is 150′ from the compressor.)

Picture: The compressed air line is reduced from 1 ½” NPT to ¼” NPT pipe.  Yes, there is a 1-1/2″ pipe bringing air close to the Super Air Knife, but it is actually a 1/4″ NPT pipe fitting on a small coiled hose that is supplying the knife. Due to a lack of air vlume, the pressure drop is huge and it is performance of the Super Air Knife.

Solution: They will need to run 1 ½” NPT pipe to the Super Air Knife.  Then uses Pipe Tees and/or Crosses to branch into the feed lines to the Super Air Knife.

Issue 2

Issue 2

Question 3: Do you have any restrictions in the compressed air line?

Answer 3: I don’t know.

Picture: We have multiple issues.

  1. The ¼” NPT compressed air line is too small (huge restriction).
  2. The red filter in photo above is too small (huge restriction). The black filter and black regulator are sized correctly to supply the Super Air Knife, but the red filter is too small causing a large pressure drop.
  3. One of the biggest culprits in choking compressed air flow to a pneumatic product are Quick Disconnect fittings. The picture below is a quick disconnect on the inlet port to the Super Air Knife (huge restriction)
  4. The yellow compressed air line is also way too small. I only bring this up because there is a difference in diameters from Schedule 40 pipe to air hose and tubing. Make sure that the inner diameters match or are larger than the recommended pipe size.

Solution: In order to have the Super Air Knife properly working, we have to make sure that it can get enough compressed air.  I had the customer remove all the small fittings, yellow tubing, quick disconnects, and the small filter.

Issue 3

Issue 3

Question 4: How many ports on the Super Air Knife are you using to supply the compressed air?

Answer 4: 2 ports.

Picture: With this length of the Super Air Knife, it requires 4 ports to supply compressed air (reference the Installation Manual). They should be evenly spaced from one end of the Super Air Knife to the other.  This is another reason that he only had compressed air coming out at the ends of the Super Air Knife.

Solution: EXAIR offers a Plumbing Kit to make sure the entire knife is supplied correctly.  The plumbing kit contains all the proper size fittings and hose to plumb the correct number of Air Knife inlets. These kits prevent you from hunting for the right fittings and from using undersized parts, which will not be able to supply the knife with enough air.

Model 9078 PKI Kit

Model 9078 Plumbing Kit

With proper installation at the beginning, it will save you time and headaches, and you will be able to utilize the EXAIR products properly. If you have additional questions about your setup, you can contact an Application Engineer at EXAIR at 1-800-903-9247.

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

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