Compressed Air Best Practices - September 2008 - (Page 52) | 09/08 Compressed Air Industry FOOD PACKAGING & PROCESSING | UTILIZING VENTURI VACUUM G E N E R AT O R S When the 18th Century Italian physicist Giovanni Venturi discovered that when air is forced through a conical nozzle its velocity increases and the pressure decreases, neither he nor anyone could conceive that it would ultimately “spawn” one of the most used and most highly controversial products used in industry today — the Venturi vacuum generator (also called ejectors). Many people, through misunderstanding, do not fully understand the benefits of this product; and, more importantly, the limitations. To further confuse the issue, various manufacturers call them different names — “pump,” “ejectors,” “vacuum transducer pumps,” etc. The most accepted general category name, in our opinion, is “Venturi vacuum generators,” which describes exactly what it does. To some, it is the “greatest thing since sliced bread.” To others, it is a constant waste of air. In the real world, the truth lies “somewhere in between” and “at the extremes” depending on the application. The Venturi vacuum generator has many advantages: p p p p p No vibration No heat generation No moving parts Vacuum on and off immediately with the air supply Will tolerate aggressive conditions very well; low cost; quick to repair or replace Can be located very close to the process, reducing the amount of evacuation air and offering fast cycle times Lightweight and mobile No electricity required Quick changeover time for service and/or component change p p p p How it Works: In its simplest form, the single-stage Venturi generator flows air through the conical Venturi orifice. As the conical orifice opens in size, the pressure falls and the velocity increases. The intensity is such that a vacuum (lower pressure than ambient air pressure) is formed and air to be evacuated from the process is pulled into the flowing air stream and blown out. The Venturi vacuum, however, does have some disadvantages: p p p Uses more air to pull a higher degree of vacuum Standard units use compressed air whenever turned on 100 psig class compressed air is more energy expensive to produce than vacuum Performance can be sensitive to compressed air supply pressure p 52 www.airbestpractices.com http://www.airbestpractices.com
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