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Holley Venturis Batman!

Posted By: Martin Thoene <martin.thoene@lakenheath.af.mil>
Date: Wednesday, 17 March 1999, at 5:52 p.m.

In Response To: I'm not so sure myself now ! (Steve Burton)

Started reading this venturi chain and figured I would expound the theories of carburettors, but Steve beat me to it. As far as I'm aware, through what I've read, and through what makes common sense (to me anyway!), the powerheads that allow air to be mixed within the impeller chamber are inherantly less efficient when used in this mode. This is because (car theory again)just as in a car brake system air is a bad thing, because it is not as easily compressed as a liquid (brake fluid). The impeller rotates at high speed and compresses molecules of liquid (water) against one another, and forces them out of the exit hole in the chamber. When air is introduced via the vent tube, the impeller now has an air/water mixture to compress, rather than the denser, pure water before. Therefore,the impeller cannot so efficiently force the water out of the chamber, plus each area between lobes now contains less water, so per revolution, less water is being moved.

As Steve said a venturi works on the principle of forcing the water through a restriction, which speeds it up AND as a by-product reduces it's pressure, thus drawing air into the reduced bore via a vent pipe. The percentage reduction in bore diameter would obviously affect the efficiency of this action, and too small a bore would also cause a restriction to water exit. Hopefully, any manufacturers of such devices will have reached a good design compromise between these two requirements.

How these two air injection methods compare as regards actual water pumped per/minuite, using the same powerhead, I don't know, but I would think that a well designed venturi would be more efficient because it's not having a direct effect on the pump impeller action.

Ain't technology fun?


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