The EXAIR Super Air Knife is a Highly Engineered and intelligently designed point of use compressed air powered device that delivers a 40:1 air amplification ratio! This simply means that for every one part compressed air supplied to an EXAIR Super Air Knife it will entrain 40 parts ambient air into the exiting compressed air stream. Almost as good as “money for nothing”! Also the EXAIR Super Air Knife is designed to provide an even or “laminar” flow of air. This is due to it being an intelligent, highly engineered compressed air product.
However if an EXAIR Super Air Knife is not connected to the compressed air supply with the appropriate number of inlet ports being fed, poor and/or erratic performance is likely. This would manifest itself as uneven air flow and lower performance from the air knife. In order to make this plumbing easier we offer optional plumbing kits for all Super Air Knives starting with the 24″ length all the way up to the 108″! The 24″ and longer Super Air Knive’s require that compressed air must be supplied to multiple air inlets along its length for optimal performance. This will ensure that the air flow is laminar and the force is even across the entire length of the Super Air Knife. All our products are shipped with an installation guide referencing the proper recommended pipe sizes for various lengths of supply pipe.
Compressed air is used to operate pneumatic systems in a facility, and it can be segregated into three sections; the supply side, the demand side, and the distribution system. The supply side is the air compressor, after-cooler, dryer, and receiver tank that produce and treat the compressed air. They are generally located in a compressor room somewhere in the corner of the plant. The demand side are the collection of end-use devices that will use the compressed air to do “work”. These pneumatic components are generally scattered throughout the facility. To connect the supply side to the demand side, a compressed air distribution system is required. Distribution systems are pipes which carry the compressed air from the compressor to the pneumatic devices. For a sound compressed air system, the three sections have to work together to make an effective and efficient system.
An analogy, I like to compare to the compressed air system, is an electrical system. The air compressor will be considered the voltage source, and the pneumatic devices will be marked as light bulbs. To connect the light bulbs to the voltage source, electrical wires are needed. The distribution system will represent the electrical wires. If the wire gauge is too small to supply the light bulbs, the wire will heat up and the voltage will drop. This heat is given off as wasted energy, and the light bulbs will dim.
The same thing happens within a compressed air system. If the piping size is too small, a pressure drop will occur. This is also wasted energy. In both types of systems, wasted energy is wasted money. One of the largest systematic problems with compressed air systems is pressure drop. If too large of a pressure loss occurs, the pneumatic equipment will not have enough power to operate effectively. As shown in the illustration below, you can see how the pressure decreases from the supply side to the demand side. With a properly designed distribution system, energy can be saved, and in reference to my analogy, it will keep the lights on.
To optimize the compressed air system, we need to reduce the amount of wasted energy; pressure drop. Pressure drop is based on restrictions, obstructions, and piping surface. If we evaluate each one, a properly designed distribution system can limit the unnecessary problems that can rob the “power” from your pneumatic equipment.
Restriction: This is the most common type of pressure drop. The air flow is forced into small areas, causing high velocities. The high velocity creates turbulent flow which increases the losses in air pressure. Flow within the pipe is directly related to the velocity times the square of the diameter. So, if you cut the I.D. of the pipe by one-half, the flow rating will be reduced to 25% of the original rating; or the velocity will increase by four times. Restriction can come in different forms like small diameter pipes or tubing; restrictive fittings like quick disconnects and needle valves, and undersized filters and regulators.
Obstruction: This is generally caused by the type of fittings that are used. To help reduce additional pressure drops use sweeping elbows and 45-degree fittings instead of 90 deg. elbows. Another option is to use full flow ball valves and butterfly valves instead of seated valves and needle valves. If a blocking valve or cap is used for future expansion, try and extend the pipe an additional 10 times the diameter of the pipe to help remove any turbulence caused from air flow disruptions. Removing sharp turns and abrupt stops will keep the velocity in a more laminar state.
Roughness: With long runs of pipe, the piping surface can affect the compressed air stream. As an example, carbon steel piping has a relative rough texture. But, over time, the surface will start to rust creating even a rougher surface. This roughness will restrain the flow, creating the pressure to drop. Aluminum and stainless steel tubing have much smoother surfaces and are not as susceptible to pressure drops caused by roughness or corrosion.
As a rule, air velocities will determine the correct pipe size. It is beneficial to oversize the pipe to accommodate for any expansions in the future. For header pipes, the velocities should not be more than 20 feet/min (6 meter/min). For the distribution lines, the velocities should not exceed 30 feet/min (9 meter/min). In following these simple rules, the distribution system can effectively supply the necessary compressed air from the supply side to the demand side.
To have a properly designed distribution system, the pressure drop should be less than 10% from the reservoir tank to the point-of-use. By following the tips above, you can reach that goal and have the supply side, demand side, and distribution system working at peak efficiency. If you would like to reduce waste even more, EXAIR offers a variety of efficient, safe, and effective compressed air products to fit within the demand side. This would be the pneumatic equivalent of changing those light bulbs at the point-of-use into LEDs.
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.
Incorrect plumbing is an all too common problem we deal with on a regular basis here at EXAIR. Many times we receive calls from a customer saying that their Air Knife isn’t producing a high velocity or they are seeing an uneven airflow. In fact we have written many blogs touching on this subject, such as the one I posted a few weeks ago titled, Proper Air Supply & Installation Provides Best Performance or the one titled Typical Compressed Air Plumbing Mistakes by our International Application Engineer John Ball.
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. We commonly reference trying to supply water to a fire hose with a garden hose, it is the same principle. Using restrictive fittings, like quick disconnects, will also contribute to this effect as the ID of the fitting is much smaller than the NPT connection size. Example: Say you are seeing 80-100 PSIG upstream of an air knife at the pressure gauge, by the time the air passes through a quick disconnect or small ID line and fitting, the actual pressure being delivered to the unit will be much less, possibly as low as 20-30 PSIG depending on the installation. One way to measure the actual pressure being delivered to the air knife would be to install a pipe tee with a pressure gauge right at the inlet of the air knife.
All of our products are shipped with an installation guide referencing the proper recommended pipe sizes for various lengths of supply pipe. When dealing with our Air Knives, since we offer lengths up to 108″, you need to plumb air to multiple inlets for knives that are 24″ and larger. To simplify the installation process, we offer our Air Knife Plumbing Kits. The Plumbing Kits include properly sized nitrile/PVC compressed air hose and brass fittings for our aluminum units. In addition, we now offer 316ss pipe and fittings for our stainless steel and PVDF Super Air Knives for applications requiring superior corrosion resistance. Using the plumbing kits eliminates pressure loss and the need for searching for the proper fittings or possibly using incorrect pipe size.
If you think you are experiencing less than expected performance from one of our products, please give us a call so we can help.