63.COMPRESSED AIR FLOW AMPLIFIERS AND BACK PRESSURE ISSUES.

Compressed air flow amplifiers (also called air movers) operate using something called the Coanda effect to convert pressure to flow with minimal energy loss. The result is high flow and less noise when used for blow off or cooling applications. However, often air amplifiers are also used for collecting and venting and/or conveying of fumes and light material.  Example are venting a tank, or even rooms because they move large volumes of air or gas.

A recent inquiry received requires a flow of 300 SCFM into a large tube of about 3 inches outside diameter. If for example a 2” air amplifier is fitted at one end, it can blow into that tube. Depending on the length of that tube there will be a back pressure.

A properly designed 2” air amplifier will amplify flow at its exit about 15 times and still maintain a good velocity to carry it into the tube. For example, whatever the compressed air use is, 15 times that will come out at the air exit. However, that “amplification” is in free space. When you add the tube to the amplified air outlet the back pressure will reduce that amplification to around 10 times for a tube about 3 meters long.  If, the tube is longer, has bends, or other internal restrictions (like a rough surface), then even more of a reduction occurs in air flow amplification.

Back pressure concerns can be offset by using larger diameter pipe, tube or hose connected to the amplifier outlet and minimizing bends and other possible restrictions.  Another method to reduce back pressure, especially if the desire is to convey a greater distance is to install in-line a compressed air venturi unit. Air amplifiers boost volume, but venturis boost vacuum. Installing them in line extends the distance you can convey and reduces the back pressure.

Regardless of the venting or conveying application, back pressure should be a consideration when utilizing compressed air operated air amplifiers.