Gas Question

Mine starts at 20 cents. It gets kind of annoying when you are in a hurry.

 

I'm pretty sure its the gas station and not your car that decides when the gas starts pouring slowly.

 

Umm... think about it. If you've prepaid in cash. It would be more accurate to stop a slower flow at the right amount than a faster flow. And if it stops before you read your mark then that means your gas tank is full...

 

its the people who you paid for the gas that makes it slow down, they have a little machine to control all the pumps

 

well i know a few times i have been in a hurry and i have passed on the 20-60 cents in gas.

i bet a few people do that every once in a while. a little more money in there pocket. im sure its not the only reason but i bet that cant hurt.

 

if you buy 10 dollars, they set it so that you get 10 dollars. no more no less

 

I think it does that because a sudden stop might create an air bubble in the pump and cause it to break...maybe...I think...

 

Can someone tell me how the gas pump knows to automatically switch off when the tank is near full?

Do they have some sort of scientist working in the back room of the gas station with computers and space technology or something?

 

It's because of the effects of water hammer:


Water hammer (or, more generally, fluid hammer) is a pressure surge or wave caused by the kinetic energy of a fluid in motion when it is forced to stop or change direction suddenly. It depends on the fluid compressibility where there are sudden changes in pressure. For example, if a valve is closed suddenly at an end of a pipeline system a water hammer wave propagates in the pipe. Moving water in a pipe has kinetic energy proportional to the mass of the water in a given volume times the square of the velocity of the water.

For this reason, most pipe-sizing charts recommend keeping the flow velocity at or below 5 ft/s (1.5 m/s). If the pipe is suddenly closed at the outlet (downstream), the mass of water before the closure is still moving forward with some velocity, building up a high pressure and shock waves. In domestic plumbing this is experienced as a loud bang resembling a hammering noise. Water hammer can cause pipelines to break or even explode if the pressure is high enough.

 

I always thought it was just to keep you from over-shooting the amount of gas you paid for, so you wouldn't have to go back inside and give the guy an extra 12 cents.

It's kind of like blowing your load early.



Actually, it's not like that at all.

 

Yup. That's right. Wow, some people are good at wild guesses.

 

The software that controls the pumps dictates how fast it slows down. It slows down because if the amount were to overshoot a pre-authorized amount on a debit/credit type transaction then you could possibly leave with free gas. The pump is authorized to pump $x.xx gas but if it overshoots and then tells the bank "ok, he pumped $x.xx + $.01 gas", the bank would decline the transaction and not charge the customer. And if you're wondering if this can happen in real life... yes... and it does... especially with some of our Canadian brothers.

If it's stopping 65 cents away from a pre-authorized amount, there's probably something wrong. lol.

 

Back when I was a kid and would prepay in cash for my gas, this one gas station would always stop it about 3 cents shy of the mark. I didn't want them taking an extra 3 cents on every transaction they did, so I'd go back in, get my 3 cents, then throw it in the trash on my way out (I didn't want a bunch of pennies in my car).

 

Is this the answer to Mr. Brightside's question?

 

Is it just me, or does this remind anyone of..

 

I've always thought that the reason the gas pump slows down (or stops in some cases, if you have the auto fill thing and let go of the handle) about 20-25 cents before the amount was so the impatient people would just say "ahh eff it, I don't have time for this!" and leave.

That's a 20 cent profit for them. And imagine if at least 10 people do it a day that's $2/day, $14/week, (grabs calculator).... $56/month, $672/year, $6,720/decade!

With that amount, you can buy yourself a decent used car every decade!

 

Just get it like this kid...

I need one of those keys.

 

All the key does is open the door to the circuitboard in the pump. Once ya get in there, you may have issues... like what to do next to get the gas to pump.

 

Yeah, I think if the little scientist in the pump is asleep, the device has an automatic way to sense the change in pressure opposing the flow of gas.

... Can I change my username to Water Hammer, or can I be a Water Hammer instead of Contributing Member?