Nov 15, 2022
It is time for an interesting new puzzler. I like this one! I hope you will too.
Anyway, here it is!
I was at the gas station a while back, with my son, when he was younger. I was putting gas in the car, like I always do.
And then my son says, "Daddy, how does the thing know when to shut off?"
Good question, I thought. We all know that when you're pumping gas, and the tank is all filled up, the handle flops down and it stops. The gas shuts off. So, I said some nonsense answer about pressure and you put the gas in and the air comes out... But it was not a good answer, because I didn't understand it myself. I couldn't really explain it to him because I couldn't explain it to myself.
So, I had to go into the archives and I found a letter that someone wrote in, asking this question. And I didn't answer it well then either. Because I didn't understand it then either!
So, it is time to answer this, once and for all.
So the question is, how does it work? What happens?
Okay time for the answer to this very interesting puzzler.
My son asked me, "How does the gas pump know when it is full? How does it decide to click off by itself, when the tank is full?"
And the answer I gave him was a nonsense answer. I knew it wasn't right! But here is the actual answer. Here's what's going on.
How does it know when the tank is full?
Here is what happens. When the gas going into the tank, it doesn't go in a steady rate. It goes into the tank in little pulses. It's called a positive displacement pump, and it pumps gas in little pulses. And you can't see that because the nozzle is stuck inside the tank.
Now, the rate in which the air pulses out of the tank is inversely proportional to the amount of air in the tank. So when there's a lot of air in the tank, and not a lot of gas, the pulse is one way. But when there is not a lot of air left in the tank, and a lot of gas and the tank is close to full, the pulse changes dramatically. It send a signal to the air trigger with that pulse, and shuts it right off.
Very interesting stuff!
