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Gas Pump Automatic Shut Off
How Does The Gas
Pump Automatically Shut Off When The Tank Is Full?
Ashish
The
extent to which various different devices and techniques have made our lives
simpler sometimes baffles me.
Almost
everything has either already become, or is in the process of becoming,
completely automated.
Take, for
example, the gas pump. Although it is mainly used to feed oil into the parched
tanks of vehicles, there are quite a few imaginative ways that people use gas
pumps; take this lady here, for example, who chooses to wash the windscreen of
her car with it.
However,
we’re not going to talk about other uses for gas pumps. We simply want to
discuss an extremely common phenomenon that you probably observe every
time you fill up the tank of your car.
Yes, you
guessed it… we’re going to figure out a bit more about the automatic
shut-off function of the gas pump nozzle.
Automatically shutting off of the pump may seem like an
“out-of-your-league” electric process, but actually, it’s not an electric
process at all.
In fact, it is a mechanical process – and a rather innovative one at
that!
It involves a very interesting physical phenomenon, known as the
Venturi effect. Let’s take a closer look.
Venturi Effect: Something You Witness Almost Every Day
The Venturi effect is one of those common phenomena that you
experience every day, but don’t know the name or even recognize the
phenomena until pointed out by a physics professor.
Don’t be frightened by the figure below; it simply depicts how fluid
pressure changes as a result of a change in the cross-section of the container.
Take any
rubber (or any other elastic material) pipe and run a fluid (water, in
this example) through it.
Now,
gently press the pipe right in the middle. What happens?
The speed
with which water flows through the pressed region (or the area where you have
applied pressure) increases.
The other
change that you may not experience here is the change in the fluid pressure in
that region (fluid pressure decreases in the compressed region).
That’s
basically what the Venturi effect is all about.
If you
understand Venturi effect, then congratulations!
Essentially,
that means you understand the basic principle behind the magical shutting off
of the pump nozzle.
All that
remains to understand now is how the whole mechanism works, which, by the way,
is quite interesting too!
When the fuel indicator on your dashboard tells you that the tank is
empty, what it’s actually telling you is that the tank is devoid of any
gasoline, but not devoid of everything.
It also contains air; as your vehicle runs and gasoline is used, the
space that it vacates is instantly occupied by air.
This means that when there is no gasoline left in the tank, it’s still
filled, but only with air.
What’s Inside the Pump Nozzle?
Next time you go to a gas pump, take a closer look at the pump
nozzle (i.e., the thing that goes inside the tank of the vehicle to fill
it).
Upon
inspection, you will find a small, half-inch hole at the end of it. If you
don’t know already, then I should tell you, this hole does not pass
gasoline to the tank.
From the
looks of it, it may seem like it just sits there idly, not doing anything at
all. But is that true? What purpose does the hole serve?
Well, that inconspicuous hole performs a very important function that
ensures that not a single drop of the precious (and expensive!) oil is spilled.
This hole is connected to a small pipe that runs into the handle. At a
point near the end of its length, let’s call it Point A, the pipes veers off in
a different direction to a diaphragm of air.
At Point A, there is a Venturi tube through which gasoline flows. This
is how the nozzle appears from the inside; but now let’s see how the whole
thing works.
How Does It Actually Work?
How the nozzle shuts off automatically with a click may seem like
magic to toddlers and adults alike, but it actually involves a very simple and
innovative process.
When the tank is not full, air is drawn from the tiny hole (of the
nozzle) to the diaphragm due to suction.
This goes on until the level of gasoline reaches the level of the hole
(or passes the hole).
As soon as the hole dips beneath the level of gasoline, it
starts to suck up gasoline.
Since the density of oil is greater than air, the Venturi tube
experiences a change in fluid pressure.
As a result, the diaphragm collapses slightly and an automatic
shut-off of the flow of gasoline through point A occurs.
What happens next is what we’re all familiar with
– the crisp click announcing a freshly full tank.
It’s
incredible how simple stuff from our daily lives can help inspire such
path-breaking techniques and make our lives easier; in this case, the employees
in charge of filling up tanks at a gas station are the real winners!
Ashish Tiwari
Digital Marketing and Content Strategist at
Science ABC
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Pressure in Segment 1 is greater than that in Segment 2, whereas the velocity of fluid is greater in Segment 2
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Giovanni
Battista Venturi, the man who discovered the Venturi effect
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