[HN Gopher] How does a gas pump know to shut itself off? (1981)
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How does a gas pump know to shut itself off? (1981)
Author : tosh
Score : 125 points
Date : 2020-10-10 18:57 UTC (4 hours ago)
(HTM) web link (www.straightdope.com)
(TXT) w3m dump (www.straightdope.com)
| CoffeePython wrote:
| 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
| zygy wrote:
| interested!
| tersers wrote:
| So if I want at least some of the benefits of the cleaning
| ingredients in the premium fuel, is the mid-grade an option?
| zachrose wrote:
| How plausible is this scene from Rambo?
|
| https://www.youtube.com/watch?v=MgfoCa2-V3g
| jMyles wrote:
| > I can probably think of some more of people are interested
|
| Sure, I'll read a few more.
| sleavey wrote:
| That text desperately needs a diagram.
| userbinator wrote:
| Even better, an animation:
| https://www.youtube.com/watch?v=_m_LSUIIUrk
| barney54 wrote:
| And here's another video explaining the safety features:
| https://youtu.be/q3phjAQZdGg
| tetris11 wrote:
| Agreed. Here's a cross view of the Venturi pump
|
| https://en.wikipedia.org/wiki/File%3AEjector_or_Injector.svg
|
| https://en.wikipedia.org/wiki/Vacuum_ejector
| tzs wrote:
| Good video explanation:
|
| https://www.youtube.com/watch?v=yx-hznTy67w
| WhompingWindows wrote:
| 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.
| keanebean86 wrote:
| My old car's charcoal evap canister had turned solid after 20
| years. This would cause pressure buildup in the tank that would
| trigger the shut-off when putting gas in. It was really
| frustrating just adding $5.
|
| This also illuminated the SES light and, more importantly,
| would have resulted in a failed emissions test. Instead of
| spending $250 on a new one I hit the old canister with a hammer
| to break up the charcoal and it was all good.
|
| Edit: Service Engine Soon
| tomonocle wrote:
| SRS light is for the Supplementary Restraint System (airbags
| and seatbelt pretensioners) so unlikely to be related to the
| filter. Might trip the MIL/Check engine light though!
| keanebean86 wrote:
| Typo... Service engine soon (SES)
| taxcoder wrote:
| Probably not the Safety Restraint System (SRS) light. Perhaps
| the Service Engine Soon (SES) light, which is often the same
| as the Check Engine Light (CEL).
|
| The hammer idea is new to me. I spent several years working
| on cars and still like to wrench on the side.
| keanebean86 wrote:
| It was a typo. SES aka service engine soon.
| taxcoder wrote:
| 10-4
| LeifCarrotson wrote:
| Seems likely you've got a defective (crimped, bent, or
| obstructed with eg. a bit of a rag) fuel filler neck.
|
| The mechanism in the pump depends on a free flowing,
| successfully venting filler neck. If a bit of detritus got into
| yours and is reducing the flow, it will do exactly that. Seems
| more likely than that every pump handle you visit is
| defective...either that or the small gas tank/bladder on your
| Prius can't accept a high enough flow rate to work with normal
| pumps, though I'd be surprised if Toyota missed that.
|
| Dropping the tank and replacing it or the filler neck is a
| pretty easy DIY project.
| sys_64738 wrote:
| You can't pump up the gas in Oregon and New Jersey.
| johnbellone wrote:
| I've never been to a station in NJ that'll touch a motorcycle.
| Unsure about if there's an exception to the law.
| Falling3 wrote:
| Funny enough the latter is my home state and the former is my
| current residence. I don't remember about NJ, but in Oregon,
| motorcyclists can legally pump their own.
| mattlondon wrote:
| 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.
|
| No wonder it seems to cost so much :)
| incanus77 wrote:
| 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.
| seattle_spring wrote:
| You weren't watching it? Do people actually engage the pump and
| then just walk away and assume it will all work out?
| dmitryminkovsky wrote:
| You don't?
|
| I've done this hundreds if not thousands of times and it only
| didn't work once, for the first time, a few months ago when I
| was filling my UHaul in Queens to move out of New York City.
| It was fitting.
| IshKebab wrote:
| What do you mean walk away? Do you guys have a lock to keep
| it on?? That seems unwise.
| loeg wrote:
| It stays in place by gravity.
| mattmaroon wrote:
| I've been doing this all my life and didn't even know it
| could go wrong. I just assume everyone inside the store did
| this too.
| mattlondon wrote:
| I was watching the price going up on the display, and not the
| actual hole in the side of the car where the fuel goes in.
|
| For UK pumps you actually need to stand there and physically
| hold the pump nozzle the whole time. If you let go it is
| spring loaded and it stops pumping.
|
| Of course, you don't have to look right at it while it is
| pumping...
| stuartd wrote:
| UK pumps still have a hole which you can push a little rod
| through to lock the pump on.
| nkozyra wrote:
| Maybe 25-20% of the pumps in the US are the same.
| loeg wrote:
| It really depends. I'd say 90+% of the pumps I encounter
| have working latches (NW US).
| tehlike wrote:
| The downsides to automation. More often than not, even if you
| are 90% of the time alert, you get fairly comfortable and not
| watching.
|
| I do watch my car while i am doing some other stuff or
| looking at my phone, but seen some other automation related
| stuff that makes me lazy. Like not locking the door at home
| when going out, because it's automatic.
| yellowapple wrote:
| Honestly, I do. My usual routine is to open the fuel hatch,
| check for card skimmers, swipe my card, punch in my phone
| number for the loyalty program (if I'm at my usual gas
| station), punch in my ZIP, grab the nozzle, select a grade,
| stick the nozzle in the hole, set the trigger on the lower
| speed, head into the store, buy beer, put the beer in the
| car, wait for the pump to finish (if somehow it hasn't), put
| the nozzle back, close the fuel hatch, and drive off on my
| merry way.
|
| This all seems to be pretty normal where I'm from.
| inopinatus wrote:
| A word of warning, all that moving around is potentially+
| building up a nice static charge on your body just in time
| for you to discharge it through the cloud of gasoline fumes
| as your hand reaches for the trigger.
|
| + (sorry)
| mehrdadn wrote:
| Yeah I was thinking the same thing, this is probably a
| bad idea. You don't want to go sit in your car either.
| leeoniya wrote:
| you'll discharge it on the grounded pump trigger before
| you withdraw anything with gas on it.
|
| static builds up everywhere, all the time during dry
| winters, yet gas stations don't regularly start exploding
| seasonally.
| inopinatus wrote:
| This isn't a theoretical concern: there are numerous
| documented cases, even multiple instances with footage on
| <popular video sharing website>.
| mehrdadn wrote:
| Here's one for sitting in a car
| https://www.youtube.com/watch?v=T6VKxmUPb3g
| yellowapple wrote:
| Well that's why I put the beer in the car before pulling
| out the nozzle: to force myself to discharge that static
| buildup.
| bfung wrote:
| Is that beer can open or closed as you pull away in the
| moving vehicle... :smirk:
| AnssiH wrote:
| I've seen similar stories before, and I'm wondering whether
| (some?) US pumps might work slower than ours? Or maybe it
| is just larger fuel tanks due to larger cars...
|
| Here in Finland typical pumps fuel 40 litres/min, i.e. 10.6
| US gallons per minute, which gets my car from near-empty to
| full in just over a minute.
|
| Does that sound similar to you?
| yellowapple wrote:
| Well so at least here in the US there are two different
| notches: one that pumps fast, and one that pumps slow. I
| always use the one that pumps slow.
|
| But 10 gallons a minute sounds about right. My car (well,
| SUV) has a 17 (?) gallon tank, and it takes a couple
| minutes to fill at that slower notch.
| j4ah4n wrote:
| Why the need for a zip code? Loyalty or something else..?
| Seems the latter considering the phrasing.
| atq2119 wrote:
| I believe it's a US credit card thing. Not sure if
| anything actually checks the zip code nowadays. A long
| time ago, I almost got stranded in the US with my
| (European) credit card, and I suspect it had to do with
| not being able to provide a fitting zip code (different
| formats).
| eigenvector wrote:
| ZIP code verification is commonly used for credit card
| authentication at gas pumps in the US, especially before
| the advent of chip & PIN.
|
| This is immensely annoying for Canadians who drive their
| cars to the US, although there are some built-in
| workarounds supported by the credit card processor such
| as punching in the 3 numerical digits of a Canadian
| postal code followed by 00.
| [deleted]
| kalium-xyz wrote:
| You cant do that in most European countries as the trigger
| will need to remain engaged for the valve to stay open. So
| you just stand there holding the pump handle bored the entire
| time. I get its more safe but I wish we had the same system
| as they do in the US
| toxik wrote:
| I have never seen a nozzle without a latch in Europe,
| however, 90% don't work and just unlatch immediately.
| Xylakant wrote:
| There's usually a little latch on the handle that you can
| engage so that the valve stays open and you can let go
| then. No need to keep glued to the pump, even in Europe.
|
| You should still watch the pump though - you're handling
| flammable substances.
| vvillena wrote:
| IIRC some European countries forbid those latches, to
| ensure the pump is always actively watched.
| CodeWriter23 wrote:
| You can always prop it open with the gas cap and let the
| diaphragm trigger described in the article do its job.
| Unless the air inlet is obstructed.
| dheera wrote:
| People seem to do it all the time in California at least.
| I've never actually seen a tank overflow but if it did it
| seems like the potential consequences could be disasterous.
|
| Maybe they should remove those flip-up latches if they want
| to prevent people from doing that.
| exlurker wrote:
| 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.
| userbinator wrote:
| 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.
| [deleted]
| ummonk wrote:
| 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.
| colechristensen wrote:
| This is incorrect, moving fluid always has lower pressure, you
| don't need the narrowing of the venturi to get suction, it just
| works better when you do.
|
| An intuitive way to think about it is to set up a straight tube
| with a fan at one end, open on the other end, with a small hole
| drilled somewhere in the side.
|
| With the fan off, clearly the pressure is the same everywhere.
|
| With the fan on though, air moves out the open end. That moving
| air has to stop once it is out of the tube, that resistance to
| the moving air at the end of the tube is dynamic pressure. The
| hole in the side though has no moving air directed at it, not
| having to resist that moving air, the pressure is less at that
| interface than at exit.
|
| If this wasn't true, you would have to be compressing the air,
| that is increasing its density. Saying a fluid is
| incompressible is equivalent to saying the speed of sound in it
| is infinite; that is obviously never true, however the effects
| of compressibility are relative to the speed of sound so as
| long as you aren't dealing with flow of hundreds of miles per
| hour in air, incompressability is a very accurate
| approximation.
| lmilcin wrote:
| Moving of fluid through a pipe always causes pressure drop due
| to Bernoulli's principle
| (https://en.wikipedia.org/wiki/Bernoulli%27s_principle). This
| is law and is unavoidable.
|
| Now, whether this pressure drop causes underpressure is another
| matter and depends on whether the effect is stronger than
| possitive pressures in the system relative to your point of
| reference (for example, outside atmospheric pressure).
|
| For example, there might be obstruction downstream which means
| there is already positive pressure in the pipe so the pressure
| drop from Bernoulli effect is lower than the positive pressure
| and you still get overpressure (Bernoulli effect is rather weak
| at slow speeds as it is proportional to square of the velocity
| of liquid in the pipe).
|
| So, in general, when you have fast flow through a pipe, a hole
| in the pipe might cause the water to flow out but it could also
| be sucking air in. It all depends on whether positive pressure
| is stronger than the effect.
| sgt wrote:
| Motorcyclists know that it may not always be bulletproof and your
| fuel tank will be dripping with fuel just after the valve shuts
| off.
| kevin_thibedeau wrote:
| I once filled up at a station in NJ where the attendants had
| disabled the spring for the self locking latch. Not a huge
| issue for a car filled from the side but with the nozzle
| pointing down into a motorcycle tank it locked itself without
| my knowledge and then I couldn't get it to shut off while gas
| was spewing all over the bike. Still alive though.
| ponker wrote:
| Isn't it illegal to fill your gas in NJ?
| bartread wrote:
| Is that job protection or something?
| [deleted]
| abruzzi wrote:
| yes, but I think for motorcycles, they let you fill on your
| own because most motorcycle tanks require a little more
| care from the filler (i.e. you don't just stick it in, turn
| it on, and wait for it to stop, instead, you're carefully
| holding the nozzle in the correct orientation and watching
| the level.)
| bartread wrote:
| I only started riding about 6 years ago, whereas I've
| been driving for 22 years (although the bike is now my
| main form of transport), so the first time I had to fill
| up a bike, like an idiot I just stuck the nozzle straight
| into the fuel tank and pulled the lever all the way like
| I would for my car... with very predictable results.
| anjel wrote:
| NJ has been a full-service only state since forever. IIR,
| Oregon is the only other state like this. Funny thing is,
| NJ has had cheaper gas (10-15% cheaper than neighboring NY
| stations where its universally self-service and a cashier.
| Yet somehow the NJ stations can afford an employee, the HR
| costs and still turn a profit for someone else.
| rubyn00bie wrote:
| Yeah, the exact figures escape me but essentially having
| someone on site to cleanup, watch things, etc costs less
| than having no one... which is one of the reasons Oregon
| mandates it, it provides jobs and has zero effect on the
| profitability of the service station.
| taxcoder wrote:
| Interesting. Any source on this?
| gruez wrote:
| Maybe NJ/NY have different tax rates on gas?
| jpindar wrote:
| Yes, for cars, but not for motorcycles (or if it is, that
| law is universally ignored).
| jdhn wrote:
| It is, but due to a quirk in the law if you have a vehicle
| that takes diesel you can pump it yourself.
| skykooler wrote:
| Interestingly there are a few smaller gas stations in NJ
| that are now self-service due to Covid.
| chrisseaton wrote:
| > Isn't it illegal to fill your gas in NJ?
|
| Huh what? You can't mean that literally?
| allannienhuis wrote:
| It's not terribly uncommon for some jurisdictions
| (sometimes at a municipal level) to not allow self-serve
| gas stations. Usually presented as a safety measure, but
| also an economic one (requires more employees).
| CamperBob2 wrote:
| In the US it's unheard-of, except in those two states.
| Oregon has recently introduced some exceptions but NJ has
| none, AFAIK.
| rokob wrote:
| Yes literally, https://www.nj.gov/labor/lsse/employee/Ret
| ail_Gasoline.html
| chrisseaton wrote:
| I wonder if they can prove that safety angle empirically.
|
| "not less than one full working day" is the training
| required.
| kevin_thibedeau wrote:
| There is a safety issue with fires caused by static
| electricity. This is most often seen with women wearing
| synthetic clothing who get back into the vehicle in the
| winter and then get a fresh charge when they step out to
| remove the nozzle. Hand touches nozzle and the vapor
| cloud goes boom. This also used to be a problem with cell
| phones with retractable antennas and you still see the
| warning signs for them from time to time.
| meddlepal wrote:
| NJ has laws mandating full-service stations because
| safety or jobs or some other long forgotten bullshit
| reason
| chrisseaton wrote:
| ...I'm going to guess that you have to tip them as well?
| ghaff wrote:
| There was never regular tipping in this case in the US as
| far as I can recall.
|
| It really went out during the gas crisis in the 70s.
| Before that, it was the norm to have full-service which
| also included washing your windshield and offering to
| check your oil (which needed to be done more frequently
| early-on). You were also often paying cash although oil
| company cards were definitely getting more common at that
| point.
|
| (But as something of an aside, I recall getting turned
| down for a gas card in the early 80s because I didn't
| have a credit history but was able to get an AMEX or
| something along those lines which helped me establish
| credit.)
| chrisseaton wrote:
| > which needed to be done more frequently early-on
|
| Americans seem to love checking and replacing their oil.
|
| They have whole retail chains devoted to it, when
| everyone I know in Europe gets it replaced once a year at
| their annual dealer service, with no checking in between.
| meddlepal wrote:
| Americans drive more than Europeans. Oil checking is
| based on mileage.
| morsch wrote:
| On a whim I dedided to double-check, you're right at
| least for residents of the USA and Germany (~21500km vs
| ~13600km average).
|
| https://www.kba.de/DE/Statistik/Kraftverkehr/VerkehrKilom
| ete...
|
| https://www.fhwa.dot.gov/ohim/onh00/bar8.htm
| ghaff wrote:
| The context of my comment was that cars used to pretty
| regularly leak oil to some degree so oil could get low on
| long drives.
|
| As the sibling comment said, oil changes are (mostly)
| distance based although, arguably, various commercial
| interests suggest oil changes more frequently than they
| are needed. But, if you drive 15,000 miles a year (as is
| common in the US), you probably want to change your oil
| more than once a year in any case.
| xxpor wrote:
| No.
|
| Most of the US was full service until the 80s. NJ and
| Oregon just never made the change.
| CamperBob2 wrote:
| It wasn't a law, just an option.
| Falling3 wrote:
| No, I've lived in each state and tipping was never
| expected (or practiced as far as I'm aware).
| lisper wrote:
| It's the same in Oregon.
| jabroni_salad wrote:
| YMMV but when I was touring the east coast the attendant
| handled the payment but I did the pumping. My preference
| anyways, you have to actually care if you want to keep the
| fuel off your paint.
| iratewizard wrote:
| As far as I know it has been for a long time.
| jeffbee wrote:
| 25-year motorcyclist here. I've never even considered it
| possible to fill a motorcycle tank while relying on the
| automatic shutoff. Do people do that? If I were to put the
| nozzle of a standard fuel pump into the hole of my tank such
| that it engages the vapor capture thing, the end of the nozzle
| will reach down almost to the bottom of the tank.
| mod wrote:
| I put the nozzle to where the tip is as near the top as I can
| get, then I let it tip and pin itself on the inside. My tank
| isn't just a hole in the top, there's some kind of metal
| "basket" in there (2020 XSR 700). I generally do then squeeze
| it by hand, but I let the auto-shutoff engage.
|
| I would feel fairly comfortable using the auto-shutoff. I
| have had it fail twice in my life. But, because the tip of
| the nozzle is so near the exterior of the tank, and the tank
| is becoming a bottleneck there, there is sometimes a little
| splashing that gets on the paint.
| emmanueloga_ wrote:
| 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).
|
| 1: https://www.youtube.com/watch?v=q3phjAQZdGg
|
| 2: https://www.convenience.org/Topics/Fuels/The-History-of-
| Self...
| LolWolf wrote:
| Yup, they still do! If it wasn't for my girlfriend (who is a
| Portland native) wouldn't have been with me, I might have ended
| up with some bruises...
| ConcernedCoder wrote:
| "the clerk almost jumped to my neck"
|
| Thanks for this, I'm always amused at how certain phrases and
| sayings get twisted-up a bit during translations between
| languages, but I'm sure you actually meant "jumped down my
| throat"...
| emmanueloga_ wrote:
| haha indeed! thx for the tip
| sokoloff wrote:
| 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.
| userbinator wrote:
| The original patent on this idea appears to be in 1925:
|
| 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.
| pgt wrote:
| 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.
| Waterluvian wrote:
| 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.
| mixmastamyk wrote:
| Also, if you know the capacity and the current level, it's easy
| to figure how much it should take to fill. I rarely fill to the
| brim anyway, only on a long trip.
| jeffrallen wrote:
| Hot damn, that was interesting!
| Lammy wrote:
| The pseudonym given to the asker ("Ethel Pumper, Dallas") is a
| great pun on tetraethyllead "ethyl gasoline":
|
| https://en.wikipedia.org/wiki/Tetraethyllead
|
| https://en.wikipedia.org/wiki/Ethyl_Corporation
| umvi wrote:
| 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.
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(page generated 2020-10-10 23:00 UTC)