When a motorist fills himself a full tank, his thoughts often flicker with an underlying fear that gasoline will now pour out of an overfilled tank. But in reality, such shots can be seen, perhaps, in old films. And the refueling nozzle has long been adapted to work so that not a single drop of fuel for the gas tank is superfluous.
It would seem that there is no particular problem in keeping track of the level of gasoline in a car's tank. Given the development of technology, any measuring sensor can come to the rescue. However, not all so simple.
As you know, gasoline is an explosive liquid. In addition, when refueling a car, the maximum concentration of fuel vapors is observed just in the filler neck of the gas tank. These conditions completely exclude the use of electrical measuring sensors. Therefore, the fuse for the filling nozzle is always mechanical.
The very same mechanism of operation of the filling pistol operates as follows: after pressing the lever, the valve stem opens and the gasoline begins to move to the tank. Then the fuel passes through a narrow ring and the so-called Venturi effect occurs - the fluid flow rate increases, and the pressure, on the contrary, decreases. Therefore, the ring is also named after the effect.
There is a small hole next to the nozzle spout that communicates with the air chamber. Through the Venturi ring, air is pumped out of the chamber, which, in fact, is replaced by atmospheric air from the sensor hole, thus avoiding the appearance of a vacuum in the chamber.
The sensor hole reacts when the fuel rises above it and blocks the flow of atmospheric air into the chamber. After that, a vacuum is formed there, which, with the help of the diaphragm retracted into place, returns the fuse rod downward. The flow of fuel stops and is accompanied by a characteristic clicking sound.
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