Proper Supply Lines are Key to Air Knife Performance

A few weeks back I chatted with a customer on an Air Knife application where they were using our 48″ aluminum Super Air Knife to remove leftover dough from a baking pan. The knife was working somewhat, but they were seeing some residual dough being left in certain areas on the pans due to what they perceived as “weak” airflow. After reading through our catalog and installation guide, they noticed that there were available shim sets that would allow them to increase the gap setting to get more force and flow out of the knife.

Available in lengths from 3″ to 108″ in aluminum, 303ss or 316ss construction

Our aluminum Super Air Knives are shipped from stock with a .002″ shim installed. The optional shim set includes a .001″, .003″ and .004″ shim that would allow you to decrease or increase the performance. By operating the Super Air Knife with the .003″ shim installed, this would increase the force and flow by 1.5 times and using the .004″ shim would double the performance. Sometimes achieving greater force and flow may be required but with the customer saying they were seeing weak airflow, it seemed there may be a restriction on the supply side.

Super Air Knife with Shim Set

I asked the customer how the knife was plumbed and what size supply lines he was using. He advised that they were plumbing air to all 3 inlets on the bottom of the knife but they were using 3/4″ hose with a run of about 30′. I advised the customer that plumbing air to all 3 inlets is required for a 48″ Super Air Knife but we actually recommend 3/4″ Schedule 40 Pipe up to 10′ or 1″ pipe up to 50′. If using hose, he would need to go up a size to maintain a large enough ID to carry the volume required for the unit. In his case, since the length of the supply is close to 30′, he would need to use 1-1/4″ ID hose.

Improper plumbing line size is a common issue we deal with here at EXAIR. Using undersized supply lines can cause excessive pressure drops because they aren’t able to carry the volume of air necessary to properly supply the compressed air device. In this particular application, if the customer were to install either the .003″ or .004″ shim, while keeping his current plumbing size, the performance would actually be worse as now the lines are even more undersized due to the increased air volume requirement from the larger Super Air Knife gap.

If you are looking to change the performance with one of our Air Knives or if you would like to discuss a particular application or product, please contact one of our application engineers for assistance at 800-903-9247.

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