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.
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.
The Plumbing Kits for our stainless steel and PVDF Super Air Knives, include 316ss cut to length pipe as well as 316ss fittings.
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.
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.
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.
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.
Many times when we provide the air consumption of an EXAIR product, we get a response like…. “I’ve got plenty of pressure, we run at around 100 PSIG”. While having the correct pressure available is important, it doesn’t make up for the volume requirement or SCFM (Standard Cubic Feet per Minute) needed to maintain that pressure. We commonly reference trying to supply water to a fire hose with a garden hose, it is the same principle, in regards to compressed air.
When looking to maintain an efficient compressed air system, it’s important that you use properly sized supply lines and fittings to support the air demand (SCFM) of the point-of-use device. The smaller the ID and the longer the length of run, it becomes more difficult for the air to travel through the system. Undersized supply lines or piping can sometimes be the biggest culprit in a compressed air system as they can lead to severe pressure drops or the loss of pressure from the compressor to the end use product.
Take for example our 18″ Super Air Knife. A 18″ Super Air Knife will consume 52.2 SCFM at 80 PSIG. We recommend using 1/2″ Schedule 40 pipe up to 10′ or 3/4″ pipe up to 50′. The reason you need to increase the pipe size after 10′ of run is that 1/2″ pipe can flow close to 100 SCFM up to 10′ but for a 50′ length it can only flow 42 SCFM. On the other hand, 3/4″ pipe is able to flow 100 SCFM up to 50′ so this will allow you to carry the volume needed to the inlet of the knife, without losing pressure through the line.
We also explain how performance can be negatively affected by improper plumbing in the following short video:
Another problem area is using restrictive fittings, like quick disconnects. While this may be useful with common everyday pneumatic tools, like an impact wrench or nail gun, they can severely limit the volumetric flow to a device requiring more air , like a longer length air knife.
For example, looking at the above 1/4″ quick disconnect, the ID of the fitting is much smaller than the NPT connection size. In this case, it is measuring close to .192″. If you were using a device like our Super Air Knife that features 1/4″ FNPT inlets, even though you are providing the correct thread size, the small inside diameter of the quick disconnect causes too much of a restriction for the volume (SCFM) required to properly support the knife, resulting in a pressure drop through the line, reducing the overall performance.
If you have any questions about compressed air applications or supply lines, please contact one of our application engineers for assistance.
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).
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.
Question 3: Do you have any restrictions in the compressed air line?
Answer 3: I don’t know.
Picture: We have multiple issues.
The ¼” NPT compressed air line is too small (huge restriction).
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.
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)
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.
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.
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.