Venturi Pump

the contraction causes the venturi effect--a low pressure area where a fluid is passing by a port at high speed. Further down the pipe, downstream from the contraction or constriction or nozzle, the pipe has returned to its normal size so the pressure and speed would be similar to the pressure and speed upstream of the venturi. The venturi effect is highly localized. If you have a bottle, you can experiment with the venturi effect by blowing across the neck of the bottle. A bottle will produce a tone as your breath creates a slight vacuum in the bottle and then air rushes in to replace it. This is also how flutes, recorders, pipe organs, and fifes produce a tone. And old-fashioned perfume atomizer involving a short tube and a rubber ball also uses the venturi effect. Squeezing the ball sends a brief, high-pressure impulse down the tube across an opening in the bottle down which another tube runs to the bottom of the bottle to access the perfume. The vacuum draws up a slug of perfume and the rapid movement of air breaks it up into tiny particles which are expelled out the open end into the air. In each of these applications, you see a very brief vacuum caused by the venturi effect, then a cycling back to normal pressures and speeds in the result downstream. In one application, this cycling results in a constant vacuum draw as a stream continuously passes a nozzle, in the second, you have a vibration as the vacuum is allowed to oscillate; and in the third you have a momentary expulsion of a vacuum aspirated liquid.