Eductor

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A device used for removing vapor or similar material, gasoline vapors, for instance, from a place where the material is not wanted.

One technique for ridding an empty gasoline storage tank of unwanted flammable vapors is the eductor method. Generally, the physical set-up for use of the method begins with the operator connecting a long, vertical, external tube to the drop tube located inside the tank. Compressed air is introduced into a fitting on this external tube. The movement of this air creates a slight vacuum in the tube and this, in turn, has the effect of drawing vapors from inside the tank up through the drop tube and into the vertical tube.

The vapors travel on through the vertical tube and are dissipated into the atmosphere, at least 12 feet above grade level. 

Meanwhile, outside air is being pulled into the tank, as a result of operation of the eductor device, through the tank’s vent piping.

Fresh air enters the tank through the vent. Vapor-laden air inside the tank simultaneously moves up through the drop tube, then through the external eductor tube, and finally out into the atmosphere.

The Venturi principle is at work in the operation of an eductor system.

See also Venturi tube.