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In a Stage II gasoline vapor recovery system, a method for creating a slight vacuum to help collect vapors from the vehicle fuel tank.
An aspirator is a suction pump in which the suction action is created as a result of the high-speed flow of fluid in an adjoining chamber. To visualize how an aspirator works, think of two hoses laid alongside each other and fastened together by tape. Imagine that at one point there is a small hole that extends through the wall of one hose and on through the adjoining wall of the second hose.
Now suppose you run a liquid, under pressure, through one of the hoses. The liquid will move at high speed. At the point where it rushes past the hole, it will have the effect of sucking in air, through this opening, from the adjoining hose. The withdrawal of air, in turn, has the effect of creating a slight vacuum in the second hose.
If the second hose were connected to a chamber containing gasoline vapor, the presence of the vacuum would suck the vapor out of the chamber and into the hose.
This principle is incorporated in some Stage II gasoline vapor recovery systems. As gasoline moves past a small aperture opening into the vapor-return line, the rush of gasoline creates a slight vacuum at the aperture. This vacuum, in turn, helps pull vapors out of the motor vehicle tank. In other words, the aspirator assists in the operation of the Stage II system. Such systems are referred to as aspirator-assist systems.
See also Venturi tube.