I worked as a maintenance technician at a gas station for 6 years before I switched into software engineering.
Some interesting things about gas dispensers/pumps:
- What most people call a gas pump is a dispenser. The actual pump is submersed inside the underground gas tank.
- mid grade gas is just premium and regular gas that is gets mixed at the dispenser before the fuel is dispensed.
- Holding the hose up high and pulling the trigger does not allow more fuel to drain from the hose after reaching your prepaid amount
- people drive off with the nozzle still in their car surprisingly often. There is a magnetic breakaway so the hose will disconnect and not pull the dispenser over.
I can probably think of some more of people are interested
I worked as a cashier in my family's gas station for a few years. I ended up doing contract development work for a retail petroleum distributor about 15 years later.
A couple of these that I can think of:
- The temperatures in our underground storage tanks were very stable, varying only by a couple of degrees F irrespective of the air temperature.
- Fuel almost always arrives warmer than the underground temperature, so you see contraction of volume on your tank monitor as newly-dropped fuel cools.
- Gross volume is the amount dispensed into the distributor's transport trucks. Net volume is the amount dropped into the Customer's tank. Gross vs. Net and temperature adjustment factors are a place where distributors play around to eke out some margin. I wrote some code that took into account air temperature at the terminal (the "rack") where trucks were filled, along with historical rack temperatures, to produce temperature-adjusted normalized costs. When you're making fractions of a cent per gallon margin every little bit helps.
In the UK, you can't "latch" it on - for flow, you need to hold the handle down constantly. This means that you are unlikely to drive off with the dispenser still in the car as there is no benefit to the driver to leave it in when they have finished.
It is interesting that it is the same dispenser design used around the world, but the latch is removed in the UK.
However, As a teenager I discovered the wonders of the latch on fuel dispensers on airfields. Then on the road I started using the removable fuel-cap as a wedge to the dispenser. eeeeek!
> Holding the hose up high and pulling the trigger does not allow more fuel to drain from the hose after reaching your prepaid amount
Doesn't it though? I feel like I know this because if I don't do it, gas pours out onto the side of my car and/or the ground, when I pull the hose out.
I was once told by an electrical engineer that the whole ban on using a cell phone near a pump was due to potential interference with how the dispenser tracks how much you have pumped.
I had a car run really badly after filling up and had a poke about. I noticed a fluid level in the fuel pipe (it had a glass site bowl thing in the fuel line). It turned out the tank of ‘petrol’ was mostly water.
> - people drive off with the nozzle still in their car surprisingly often. There is a magnetic breakaway so the hose will disconnect and not pull the dispenser over.
I've done this at least once that I can remember, and maybe twice or more. Yep, the handle just popped right off. Embarrassing but fortunately not dangerous.
Any truth to the rumor that you should avoid filling your car when the main station tank is getting refilled? Think the logic was that their refilling would stir up sediment and potentially damage your car’s engine.
I was filling up one time when the person on the opposite side of the pump drove off with the nozzle still attached. Once the end broke away, the rest of it snapped back and slammed into the other side of the pump enclosure so loudly and violently that it set off my adrenaline and I was freaked out for a good few minutes. Quite an experience!
Long time ago I read somewhere you shouldn't hold the lever all the way because it could potentially allow more oxygen through and thus have to pay just a little bit more for the same amount of fuel. Is that really true or was I being gaslighted?
> mid grade gas is just premium and regular gas that is gets mixed
There is nothing else "premium" about premium gas, than that it can be compressed more in the engine. Compressibility is measured by the octane rating, so it makes sense than mixing 87 octane gas and 91 octane gas, gives you 89 octane gas (using the American octane scale, Europe uses a different scale).
At what point in the distribution chain is ethanol added? I prefer to run ethanol-free fuel when possible, but would also prefer to use fuel with good detergent additives. I've always wondered if the gas at the local ethanol-free station is missing the additive package as well.
Does anyone still use above-ground tanks? Just wondering if there's any truth to buying gas in bulk during cold weather for density reasons.
(though I'd imagine the price/barrel has been fluctuating more than the temperature would cause lately)
From what I heard, pretty much all gasoline starts off the same in the US, the brands will add a tiny amount of their own detergent on top of what's already in the base. Seems plausible.
Hands down the most fascinating part of this thread is the number of comments from people saying "in the US x is different" or "in State y it works this way". You go on reading and you see people contradicting each other because of course, different States, different solutions; different towns, different solutions.
It goes to show how much people think they know their country, to what degree they believe to know everything there is to know about their culture, history, and surroundings. Really though, we know very little despite what we tell ourselves or others.
I guess the message is: travel a little people. Even if it's just to the neighboring State for crying out loud.
Funny, I found myself asking this question recently too. Also, who made them.. I wish some of these industrial everyday products had the name of the designer attached. Found a video which has a nice nozzle teardown [1].
Another interesting thing is the story of self-fueling, an study in slow adoption. Apparently, the current state of affairs was reached by 1980s or so [2].
I remember driving from California to Oregon, getting to a gas station and trying to pump my own gas... the clerk almost jumped to my neck (in my memories at least :-p).
Doesn't always shutoff! I was filling up one of my cars a year or two ago, watching the meter tick up and up and up so not watching the pump handle/nozzle itself, just cursing the price of a full tank etc.
Someone in the car behind actually jumped out and came over to let me know that my tank was overflowing and going all over the floor.
One of my old coworkers used to totally and completely trust the auto shutoff. To the point that he didn't even stop the pump before pulling it out of the car. He would just yank the still running pump out and it would shut off. One day he comes in to work complaining about how the pump he used the day before didn't work and he got covered in gasoline.
We all just looked at him incredulously when he explained what happened.
I had an incident where a customer told me "they spilled some gas". I go out to see ~20 gallons of gasoline on the ground (my best estimate - was a puddle about 16 ft x 6 ft x 1/2 inch deep)".
They were filling a huge motorhome, so it would take a while to fill regardless and they weren't paying attention.
I should have called the fire department, but was a dumb teenager working alone. Threw a few buckets of absorbent on it. It was over 90F that day and windy, so it took 10 min for most of it to evaporate.
The design uses a vacuum to trip the shutoff, and that's created by the liquid moving through the venturi, so one of the things that can cause it to not work, besides wear and damage, is if the liquid is moving too slow to generate enough vacuum to actuate the mechanism.
Haha, same happened to me in Spain two years ago. I stood there minding my own business like a doof until someone on the other pump were like, "Yo!! Watch out". Wasn't much, but still surprising.
This happens to me sometimes, too, though I drive a 1985 VW van. It seems to be related to the nozzle fit and holding it very firmly, but I find that today's pumps are pretty heavy, require a very firm squeeze, and are hard to hold just right. Maybe it's just an Oregon thing, where we are not allowed to pump our own gas. I've had licenses in four other states and gassed up myself plenty of times. Whenever I'm in Washington or other states with my van, I tend to let the auto-hold engage.
The claim about Bernoulli effect would be flat out wrong. Moving fluid that has been pumped into motion doesn’t normally have lower pressure than the ambient pressure (i.e. exit pressure). Wikipedia better explains it - they’re using a venturi pump - i.e. there is a construction in the tube that causes the fluid to have faster speed and lower pressure than the exit.
I have a 2008 Prius and the gas pump repeatedly "shuts itself off" due to a faulty mechanism within the gas tank. Certain pumps are too high pressure and they trip the shut-off very easily, other pumps if I hold it at just the right angle, the gas will flow through. It's super tough on some pumps, it took me 30+ tries to get it to continue flowing at the last fill-up.
About 1/4 the time the pump is either shutting off every 5 seconds or doesn’t shut off. But luckily there’s a subtle but obvious sound of the tank being almost full and I’m standing right there.
I sat next to a guy in the petrol pump business once on a flight from a time before time (pre-COVID), so I asked him how the pump knew when to stop: he explained that the handle contained a rotating cylinder (halved in the middle) with a known volume V that rotated N times until V*N = Purchased Liters.
I've been reading The Straight Dope at least intermittently since the mid 80s. It's been a wonderful source of esoteric trivia and it's finally come to an end. There might be something taking its place but for now it's over. https://www.straightdope.com/21374450/a-note-from-cecil-adam...
I bought a car ~7 years ago in Illinois and transported it to California. Pumps in IL worked fine with the car, but upon arriving in CA, I found that gas pumps will prematurely shut off, almost immediately upon pumping, regardless of how empty the tank is. In order to prevent the premature shutoff, I have to lift the pump hose at about a 45 degree while pumping.
Any idea what's going wrong here? Is it my car or the pump? Is there a difference between the pumps in IL vs CA?
I've often wondered this myself. Also, because on a couple of occasions, I've had a gas pump (or dispenser?) turn off immediately if I inserted it all the way, but it would work fine if I retracted it a little bit (which made me nervous, because will it still turn off automatically in time if I do that?).
So how is it possible that on some pumps, this trigger system immediately disables the main valve, even when the tank is empty? My best guess is that it's not actually contact with gas in the tank that shuts it off, but air pressure. Air pressure stays constant if I don't insert the handle all the way, but if I do, maybe the air pressure can build up a bit?
So despite Cecil's answer, I still have questions.
You know, half of the reason I come to HN is because it seems like every other thread had someone with a random life experiences to share, like the surprising number of people here with experience is the gas-pumping field.
A drawing would have been nice. Also when mentioning the Bernoulli effect, petrol, cars and it is 1981, then I would like to add that this is the same effect your carburetor uses.
I love mechanisms that rely on laws of physics other than electromagnatism. Seems like in 2020 we reach for the almighty transistor before considering alternative physical solutions.
For some reason that I can’t figure out, the dispenser shutoff doesn’t work reliably on my 65 or 66 Mustangs, or at least not fast enough to prevent spillage. Maybe the very short fuel filler hose (from the cap to the top of tank is only maybe 12” of high capacity bent tubing).
If I’m not listening for the noise/pitch change to manually stop, it’s going to splash plenty of gas out the back when the tank fills.
[+] [-] CoffeePython|5 years ago|reply
Some interesting things about gas dispensers/pumps:
- What most people call a gas pump is a dispenser. The actual pump is submersed inside the underground gas tank.
- mid grade gas is just premium and regular gas that is gets mixed at the dispenser before the fuel is dispensed.
- Holding the hose up high and pulling the trigger does not allow more fuel to drain from the hose after reaching your prepaid amount
- people drive off with the nozzle still in their car surprisingly often. There is a magnetic breakaway so the hose will disconnect and not pull the dispenser over.
I can probably think of some more of people are interested
[+] [-] EvanAnderson|5 years ago|reply
A couple of these that I can think of:
- The temperatures in our underground storage tanks were very stable, varying only by a couple of degrees F irrespective of the air temperature.
- Fuel almost always arrives warmer than the underground temperature, so you see contraction of volume on your tank monitor as newly-dropped fuel cools.
- Gross volume is the amount dispensed into the distributor's transport trucks. Net volume is the amount dropped into the Customer's tank. Gross vs. Net and temperature adjustment factors are a place where distributors play around to eke out some margin. I wrote some code that took into account air temperature at the terminal (the "rack") where trucks were filled, along with historical rack temperatures, to produce temperature-adjusted normalized costs. When you're making fractions of a cent per gallon margin every little bit helps.
[+] [-] keithnz|5 years ago|reply
One of the main guys who worked on the pump software, in forth, actually wrote a book where the petrol pump is his main example https://www.manning.com/books/functional-reactive-programmin...
[+] [-] TedDoesntTalk|5 years ago|reply
I did this in the late 80s. The handle ripped off and was not magnetically attached. However, gas did not spill from the hose.
I drove back to the station and handed it to the attendant sheepishly. He said thanks.
[+] [-] Daviey|5 years ago|reply
It is interesting that it is the same dispenser design used around the world, but the latch is removed in the UK.
However, As a teenager I discovered the wonders of the latch on fuel dispensers on airfields. Then on the road I started using the removable fuel-cap as a wedge to the dispenser. eeeeek!
(Now I use an electric car)
[+] [-] twosheep|5 years ago|reply
[+] [-] hackmiester|5 years ago|reply
Doesn't it though? I feel like I know this because if I don't do it, gas pours out onto the side of my car and/or the ground, when I pull the hose out.
[+] [-] dwd|5 years ago|reply
Is there any truth this?
[+] [-] lostlogin|5 years ago|reply
I had a car run really badly after filling up and had a poke about. I noticed a fluid level in the fuel pipe (it had a glass site bowl thing in the fuel line). It turned out the tank of ‘petrol’ was mostly water.
[+] [-] autarch|5 years ago|reply
I've done this at least once that I can remember, and maybe twice or more. Yep, the handle just popped right off. Embarrassing but fortunately not dangerous.
[+] [-] uptown|5 years ago|reply
[+] [-] zachrose|5 years ago|reply
https://www.youtube.com/watch?v=MgfoCa2-V3g
[+] [-] swivelmaster|5 years ago|reply
[+] [-] chmod600|5 years ago|reply
[+] [-] RedShift1|5 years ago|reply
[+] [-] baby|5 years ago|reply
[+] [-] sampo|5 years ago|reply
There is nothing else "premium" about premium gas, than that it can be compressed more in the engine. Compressibility is measured by the octane rating, so it makes sense than mixing 87 octane gas and 91 octane gas, gives you 89 octane gas (using the American octane scale, Europe uses a different scale).
[+] [-] CamperBob2|5 years ago|reply
[+] [-] anon_cow1111|5 years ago|reply
[+] [-] jMyles|5 years ago|reply
Sure, I'll read a few more.
[+] [-] xellisx|5 years ago|reply
[+] [-] tersers|5 years ago|reply
[+] [-] laurent92|5 years ago|reply
[+] [-] BayesStreet|5 years ago|reply
[+] [-] richev|5 years ago|reply
Yes please!
[+] [-] senux|5 years ago|reply
It goes to show how much people think they know their country, to what degree they believe to know everything there is to know about their culture, history, and surroundings. Really though, we know very little despite what we tell ourselves or others.
I guess the message is: travel a little people. Even if it's just to the neighboring State for crying out loud.
[+] [-] userbinator|5 years ago|reply
http://patentimages.storage.googleapis.com/pdfs/US1550738.pd...
Later patents improve on the design:
http://patentimages.storage.googleapis.com/pdfs/US2320033.pd... (1943)
http://patentimages.storage.googleapis.com/pdfs/US2582195.pd... (1952)
http://patentimages.storage.googleapis.com/pdfs/US2675952.pd... (1954)
http://patentimages.storage.googleapis.com/pdfs/US2686626.pd... (1954)
http://patentimages.storage.googleapis.com/pdfs/US2821212.pd... (1958)
IMHO they are well worth reading just for the diagrams alone.
[+] [-] emmanueloga_|5 years ago|reply
Another interesting thing is the story of self-fueling, an study in slow adoption. Apparently, the current state of affairs was reached by 1980s or so [2].
I remember driving from California to Oregon, getting to a gas station and trying to pump my own gas... the clerk almost jumped to my neck (in my memories at least :-p).
1: https://www.youtube.com/watch?v=q3phjAQZdGg
2: https://www.convenience.org/Topics/Fuels/The-History-of-Self...
[+] [-] mattlondon|5 years ago|reply
Someone in the car behind actually jumped out and came over to let me know that my tank was overflowing and going all over the floor.
No wonder it seems to cost so much :)
[+] [-] seattle_spring|5 years ago|reply
[+] [-] RandallBrown|5 years ago|reply
We all just looked at him incredulously when he explained what happened.
[+] [-] refurb|5 years ago|reply
I had an incident where a customer told me "they spilled some gas". I go out to see ~20 gallons of gasoline on the ground (my best estimate - was a puddle about 16 ft x 6 ft x 1/2 inch deep)".
They were filling a huge motorhome, so it would take a while to fill regardless and they weren't paying attention.
I should have called the fire department, but was a dumb teenager working alone. Threw a few buckets of absorbent on it. It was over 90F that day and windy, so it took 10 min for most of it to evaporate.
[+] [-] userbinator|5 years ago|reply
[+] [-] exlurker|5 years ago|reply
[+] [-] incanus77|5 years ago|reply
[+] [-] sleavey|5 years ago|reply
[+] [-] ummonk|5 years ago|reply
[+] [-] Lammy|5 years ago|reply
https://en.wikipedia.org/wiki/Tetraethyllead
https://en.wikipedia.org/wiki/Ethyl_Corporation
[+] [-] WhompingWindows|5 years ago|reply
[+] [-] Waterluvian|5 years ago|reply
[+] [-] pgt|5 years ago|reply
[+] [-] dhosek|5 years ago|reply
[+] [-] matmann2001|5 years ago|reply
Any idea what's going wrong here? Is it my car or the pump? Is there a difference between the pumps in IL vs CA?
[+] [-] sgt|5 years ago|reply
[+] [-] mcv|5 years ago|reply
So how is it possible that on some pumps, this trigger system immediately disables the main valve, even when the tank is empty? My best guess is that it's not actually contact with gas in the tank that shuts it off, but air pressure. Air pressure stays constant if I don't insert the handle all the way, but if I do, maybe the air pressure can build up a bit?
So despite Cecil's answer, I still have questions.
[+] [-] civilian|5 years ago|reply
Really helped me understand what was going on.
[+] [-] jedimastert|5 years ago|reply
[+] [-] andi999|5 years ago|reply
[+] [-] umvi|5 years ago|reply
[+] [-] sokoloff|5 years ago|reply
If I’m not listening for the noise/pitch change to manually stop, it’s going to splash plenty of gas out the back when the tank fills.