Tech Hidden In Plain Sight: Gas Pumps

Ask someone who isn’t technically inclined how a TV signal works or how a cell phone works, or even how a two-way switch in a hall light works and you are likely to get either a blank stare or a wildly improbable explanation. But there are some things so commonplace that even the most tech-savvy of us don’t bother thinking about. One of these things is the lowly gas pump.

Gas pumps are everywhere and it’s a safe bet to assume everyone reading this has used one at some point, most of use on a regular basis. But what’s really going on there?

Most of it is pretty easy to figure out. As the name implies, there must be a pump. There’s some way to tell how much is pumping and how much it costs and, today, some way to take the payment. But what about the automatic shut off? It isn’t done with some fancy electronics, that mechanism dates back decades. Plus, we’re talking about highly combustible materials, there has to be more to it then just a big tank of gas and a pump. Safety is paramount and, experientially, we don’t hear about gas stations blowing up two or three times a day, so there must be some pretty stout safety features. Let’s pay homage to those silent safety features and explore the tricks of the gasoline trade.

Gravity Pumps of the Old Days

Many old gas pumps had manual pumps, a big glass tank at the top, and a siphon hose with a stopcock. If you wanted, say, 5 gallons, the attendant would pump the gas from the underground tank into the big glass tank that had measurement marks on it. Once it held the requisite amount, the hose would go into your gas tank, the attendant would open the stopcock, and gravity would do the rest.

Oddly, the gas pump predates the automobile. Sylvanus Bowser sold a pump as early as 1885 to sell kerosene that people used in lamps and stoves. In some parts of the world, a gas pump is sometimes called a bowser, although in the United States that term usually means a fuel truck for aircraft.

Obviously, this is a simple arrangement but ripe for improvement. But with the proliferation of pumping stations, and microcontrollers decades away, designers had to do some clever electromechanical work to make a functioning pump that could be used without skill or even by the customer themselves.

Mid-Grade: The Cocktail of the Filling Station

At the core of it all are large underground tanks that hold the gas. Trucks periodically stop by and refill these tanks. Fun fact. The Exxon truck and the Texaco truck get their gas at the same place that the Shell truck does. Either at the terminal or at the point of delivery, special additives are mixed in with the gas. That’s what makes one gas of the same octane rating different from the other brands.

The trucks usually have a few different compartments. One for regular gas, one for premium, and one for diesel. Some have more compartments. However, there is usually no mid-grade gas. When you buy midgrade gas, you are really just mixing regular and premium together right in the pump. This is accomplished with a blend valve. This is two valves connected in such a way that when one is open, the other one is closed in proportion so that the total flow is always equal to 100%. For example, if one valve is at 100% the other is always at 0%. But if you turn the first valve to 60%, the second valve will be at 40%. This allows the exact mix of two fuels into an intermediate grade.

The additives are very important for modern engines. In 2004, automakers were concerned that some gas didn’t have enough detergents to prevent carbon buildup effectively. With higher compressions, direct injection, and other modern engine techniques, this is more important than ever. They formed the TOP TIER standard that gas producers could certify against. AAA found that using TOP TIER gas did produce fewer deposits in the engine than the minimum standard gas. Of course, brands that are not TOP TIER may be the same or better, they just aren’t tested.

Automatic Shutoff

The most amazing part of the gas pump is how it somehow knows — even with old tech — that the tank is full. The video below from [BrainStuff] shows a good diagram. There’s a small hole near the end of the nozzle that has its other end near a flexible diaphragm and a Venturi tube.

The Venturi effect causes a pressure drop when you compress a moving fluid. For example, if you squeeze a rubber tube in the middle, whatever is flowing through the tube will be at a lower pressure after the compressed part of the tube.

Before leaving the nozzle, a narrow part of the fuel path in the handle compresses the fuel, causing a lower pressure area after this bottleneck. The diaphragm inside the handle expands because ambient air pressure (which enters through the small “safety” tube hole at the tip of the spout) is higher than the low pressure fuel area created by the Venturi effect.

Gas pump nozzle cutaway shows the Venturi valve diaphragm. The demo video from Husky Corporation mentions that more modern nozzles have additional safety features.

When the rising level of fuel blocks the hole at the tip, it causes the suction to stop, the diaphragm collapses, and the fuel valve springs shut with a loud click. No electronics at all. Just a flexible diaphragm, a tube, a spring, and some clever arrangement of all the parts.

Richard C. Corson originally came up with a version of the automatic shutoff in 1939 and received a patent in 1942. He had noticed workers had to fill barrels one at a time so as not to overfill and was inspired by the operation of a toilet to come up with an automatic valve.

Flow Metering

Gasoline is difficult to meter accurately. There’s a diaphragm that constricts the flow to a known rate. The diaphragm also expands to slow down when you approach the point where the pump will shut off (for example, if you asked for $10 worth of gas). The metering itself is usually a 4-stroke piston flow meter that sends data to the onboard controller. In the old days, it just drove the little dials that showed the price. Piston flowmeters are very accurate. The video below from [Max Machinery] shows how they work.

Gas has a thermal expansion coefficient at 20C of over 4 times that of water. When you buy gas in bulk, the amount is usually compensated for temperature and some countries, like Canada, have done this at the retail level, too.

Hidden in Plain Sight

Next time you are pumping gas, you’ll have something to think about. There’s a lot of technology out there that someone is an expert on, but most of us just take it for granted. You have to admit, there’s probably a lot more to it than you would have thought.

If you are interested in the Venturi effect, you can make 3D printed Venturi tubes. If you thought about using your old car’s fuel pump to cool your PC, you might want to think again.

67 thoughts on “Tech Hidden In Plain Sight: Gas Pumps

      1. He said fluid not liquid.

        According to wikipedia “Fluids are a phase of matter and include liquids, gases and plasmas. They are substances with zero shear modulus, or, in simpler terms, substances which cannot resist any shear force applied to them.”

        Even so liquids are compressible, just not very much. I did a google search and the website says that water at the bottom of the ocean is under about 150 times the pressure of the atmosphere and is only about 1% denser as a result.

  1. As a former fuel truck driver, I would like to point out a correction to your story. Gasoline products are not blended at the pumps, or at least they haven’t been for the last 20 years. I worked for a company that specialized in fuel delivery in the Midwest that delivered products to various customers, such as gas stations, mining operations and airports. Products were always blended to their final form at either the pipeline terminal or the refinery while loading. Fuel additives required by each brand, dye for off-road diesel and ethanol if needed were injected directly into the loading spout as the fuel was pumped into the trailer at up to 600 GPM. Like you pointed out, most trailers have multiple compartments, with the bigger ones usually having 5-6 compartments of differing sizes capable of holding up to a total of 11,000 gallons or so. With the exception of Jet A and Avgas, compartments aren’t restricted to one type of fuel. We would routinely load gas into a compartment that previously held diesel or vice versa. The only requirement was to ensure that any remaining product (usually no more than a 1/2 gallon or so) was dumped into the fuel point’s sump for return to the refinery for re-processing. Fuel products aren’t considered contaminated unless there is 10% or more of a different grade in the tank. For aviation products a company will have usually have a dedicated trailer since certification is much more stringent and requires an inspection every time the tank is loaded.

    1. Too bad my memory is 20 years old (I left a job in 2000 programming a controller that talked to pumps), but I remember that blender pumps were a thing back in the late ’90s. Sell up to five grades (usually three) to make the customer feel like having many choices, and only have to re-stock two tanks! But this was in Texas, so not as many “botique blends” to keep track of, and I only ever remember it being done for retail sites. (This was one of three jobs I’ve had where WalMart was a customer!)

      1. And it could be that other parts of the country do still use blender pumps. I admit that I have only delivered in the upper Midwest parts of the country, but I’ve worked with guys that did delivery in Arizona, California and several other states in the southwest, and they said operations were essentially the same there. The grades we mostly deal with here are a Regular – straight 85 octane, Mid – 85 oct with 10% ethanol added to bump the octane to 87), sometimes a ‘Super Midgrade’ – 40% 85 oct, 40% 91 oct & 10% eth for an 89 octane rating, and a premium which was either 91 or 93 octane depending on if ethanol was added. All of the blending was done at the pipeline or refinery though, and each station had a separate tank for each grade of product that they carried. As a delivery driver, you REALLY did not want to mix up tanks when delivering. The results could be very expensive!

        1. The other idea of the blender pumps is Wawa’s in Florida. Least where I am all of them offer “boat gas” this is real gasoline(non-ethanol) you would have bought in the 90s or earlier before they stated blending in ethanol. Cost of this non-ethanol is typically about 50 cents a gallon more than regular. Do they actually have a separate non ethanol tank. Or do they just have all non-ethanol and blend in the 10% ethanol onsite? This non-ethanol is sold in a blue colored handle and it’s not like diesel where the pump spout is bigger to keep people from accidentally putting diesel in their gas car. Absolutely nothing stops you putting this non-ethanol gas into your car which I always do, especially now barely driving my car cause of covid. I just went 8 months between fillups. Non-ethanol gas stores better in a humid environment. The ethanol absorbs water, which is why the non-ethanol is sold a “boat gas”

          1. The ethanol also corrodes aluminium parts, and the effect starts to increase beyond 5%. That’s why manufacturers don’t recommend using ethanol blended fuels for older cars that are not designed with flexi-fuel capability in mind.

      2. I’m pretty sure blender pumps are still in use. 7/11s here in Florida typically have 5 or 6 different grades you can pick from. I’m 100% certain they don’t have that many tanks underground. Actually not that hard to tell, look how many filling manholes there are that the refueling trucks use. I typically see 3, so the assumption is regular gas, premium gas and diesel. All the blending has to be done onsite somewhere likely in the pump.

        1. But it’s possible the other way round: 5 filling manholes and only gas (95 oct) and diesel for sale. This is from the time when there were 3 kinds of gas, like regular 91, 95 and leaded 98.

      3. I remeber, when I was a child, in the 1970ies, perhaps 1980ies there were “Mix” pumps where you could get 25%, 50% or 75% of “super” mixed with the rest regular gas. At that time all leaded gas.
        I think that ended with the introduction of 91 octane regular, 98 octane was still leaded for cars that needed it. I think this was to discourage people from using leaded gas, if they did not really need it. Then the 95 octane unleaded “eurosuper” came and now this is in reality the normal gas, if you do not buy a special premium or “racing” or oherwise fance namend much mor expensive product with 99 or 100 octane.
        If a gas station offers “91 octane” it is in reality 95 and the price is mostly the same. Sometimes there is a difference of 0.1 cent, but purely for marketing reasons :-)

    2. I think the blending they were referring to was to create mid grade gasoline as 89 octane is not available at the loading rack. As far as additive, I have as a driver had to manually add the BP additive when the injector at the rack was not operating. BTW join the National Petroleum Carriers Club on Facebook.

      1. We had a few stations that carried 89, but that was a less common grade in this area. For us, those products were also blended at the rack, and they would use a separate tank for that grade. I’ve also had to add additives manually for the same reason. That usually only happened when it was -20 and the injectors were frozen. What fun it is to climb on top of a trailer in that weather! Fortunately I got out of a truck 5 years ago and don’t have to deal with that any more.

    3. I managed a gas station from around 1992 thru 2007, in the beginning there were 3 gasoline tanks, reg, mid or plus and prem, the mid or plus was blended in the tank at usually 60% prem and 40% reg. Newer pump technology came along to eliminate the need of the mid or plus fuel tank, there was a blend valve for when you wanted mid or plus, the only problem is if you run out of reg or prem gas, you also can’t pump mid or plus. Yes, there a lot more amazing things involved in the whole fuel delivery system.

    4. Sorry, but I work for a company that installs gas station equipment, and blenders outnumber pure-product dispensers 100:1. Sites that still have Regular/Plus/Premium tanks usually abandon Plus as a product by replacing their pure-product dispensers with blenders for plus and fill the plus tank with diesel or non-ethanol gas.

    5. You are misinformed. Some pumps do blend the gas. Ive been the parts and equipment buyer for over 20 yrs. They have a a blend valve in the bottom of the pump before it trans in to the meters that count the amount. In Texas the 89 octane is blended 65% 87 octane and 35% 93 octane.

    6. Mike,

      I’m a pump tech. Midgrade is most definitely blended at the dispenser. You don’t see many midgrade UST’S anymore. I’ve worked all across the south and you will very rarely find a midgrade tank. If a new station is built. 100% gaurantee they will be blending at the dispenser.

    7. I am a lead tech at a Petroleum Solutions company. Install and repair stations. Every manufacturer has a blender pump. Mid grade is 90 percent of the time blended in the dispenser.

    8. I would have to disagree with your comment on blending I install blenging dispensers weekly so I know for sure that we make the mid grade on site more often than not. Plus some have dispensers that inject cleaners into the fuel at the station.

    9. GAS PUMPS ABSOLUTELY BLEND AT THE PUMP. And as the article suggest at mainly a 60/40 blend(even though the price per gallon is in 10 cent increments) And I’m not talking about 20 year old pumps either. Since when does a truck driver know the inner-workings of a gas pump? I am a current, fully certified Glibarco/Veeder-Root service technician/inspector/installer in California. We lead the nation in both new pump technology and emissions restriction, and most of the gas pumps have blending 3 way valves. Only a couple of stations are even left with mid grade straight product and are quickly being retro fitted to allow for an e-85/ bio-diesel #2 split tanks. And although you clearly know at what flow rate a fuel delivery truck gets filled at, you are hardly qualified to discuss how these actually work. From multi geared siphon turbines with Venturi and 3 way valves, all the way up to the tank monitoring system and point of sell unit and the network it connects to, you are completely out of your element, and should conserve you attentions to not falling asleep behind the wheel and putting your hose in the correct tank. Which is apparently a problem for you load delivery drivers since I get 3 calls a month from store owners who have gotten delivery’s in the wrong tanks. You are also completly wrong about the “Fuel products aren’t considered contaminated unless there is 10% or more of a different grade in the tank.” statement. Gasoline needs to have an octane rating of 87-91 to fit today’s car engines. Diesel fuel has an octane rating of 25-40. Mixing 2% diesel fuel into gasoline will lower the overall octane rating by 1 point. Getting 10% diesel contamination lowers octane by 5 points, which is enough to create problems in most engines. The octane depression rises linearly with increasing percentages of diesel fuel in the gasoline. And that’s just the first potential problem. Because diesel fuel is heavier than gasoline, it can sink to the bottom of your gas tank, resulting in the injection of both gas and diesel into the intake manifold or the cylinder. Depending on the mix, you can get partially-burned diesel fuel which leaves bigtime deposits on pistons, valves and spark plugs. You get a car or truck that runs terrible, and if you keep driving it, you can cause serious damage. If enough diesel fuel gets in the cylinder, you can hydro-lock the cylinders, resulting in a blown head gasket, cracked cylinder head or other serious problems that can lead your vehicle down the road to a quick and final death. This diesel fuel in the cylinder can also seep past the piston rings into the oil crankcase, diluting the lubricating oil. This can damage all internal engine lubricated parts resulting in major engine failure from rapid wear. If unburned diesel fuel makes its way into the exhaust system, it will ignite in the catalytic convertor. The fire will plug the holes in the catalyst, destroying it and leaving you with a repair job well into the four-figures.

      THANKS TRUCK DRIVER!!!!!!!!!!!!!

      And if done by putting oct gas into a diesel The first thing it’s going to do is depress the flash point of the diesel, which can be dangerous given that pockets of higher concentrations of gasoline can develop in a tank. So the flash point wouldn’t be consistent throughout the entire tank.Given the large difference in flash point temperature between gas and diesel, it doesn’t take very much gasoline to depress the flash temperature significantly. As little as 1% gasoline contamination will lower the diesel flash point by 18 degrees C. This means the diesel fuel will prematurely ignite in the diesel engine, which can lead to engine damage. Gasoline contamination can also damage the fuel pump and mess up diesel injectors. This happens because of a drop in lubrication. Simply speaking, gasoline is a solvent while diesel is an oil. Diesel has enough lubricity to lubricate the fuel pumps and the injectors. Swapping in some gasoline takes away this lubrication, leading to damage. Beyond these, you’ll get incomplete combustion, initially characterized by large amounts of black smoke. Beyond being an aesthetic problem, the vehicle’s computer will try to compensate for this combustion lack by adjusting the fuel-air mixture. This is going to cut your power and performance considerably. And if you continue to use the fuel, you can cause real damage to the vehicle’s computer sensors by either overheating them or covering them in soot such that they can’t detect anything.

      Next time try and comment on subjects you are actually educated in. Instead of correcting peoples hard work.

    10. They do I fact blend at the pump but now it’s done by the computer base. Gilbarco pumps use a 100% to 0% blend using the 87 grade as being the main product flow then the pump node adjust how much 91 is allowed in to make that mid grade of 91 octane here in California. Wayne dispensers do the same thing but reversed using 91 as the main then metering in 87 to make mid grade. They use to use mechanical blenders way back but not anymore. For calibrating said pumps you just calibrate each grade 87 then 91 then you check 89 to make sure it’s within tolerance. If it’s in you are golden and the dispenser is doing the blending. You have blend ratios you program into the dispenser upon start up.

    11. Hate to contradict you, but in fact almost all multi product dispensers MPD that have more than two grades are actually blending the product. There is one correction or clarification required however. Almost no modern gas pumps have pumps. The pumps are located in the storage tank. The thing we call a gas pump is in fact a gas dispenser.

      Weights and measures fluids specialist for 35 years. Major part of what we do is testing fuel meters for accuracy.

  2. One thing that I am sure no one pays attention to is the TV screens impeded in the pumps. It gets annoying when all the pumps start playing the same commercial but each with a 1 sec delay. It’s like being in an echo chamber. 😄

      1. Originally it wasn’t a nanny state thing; it was that when the big switch to unleaded gas was made in the early 70s, cars with catalytic converters had restrictor plates in their fuel filler pipes to prevent filling them with leaded gas (the new unleaded nozzles were smaller in diameter). This done in order to not destroy the catalyts with the lead, but a lot of people were knocking out the restrictor plates because unleaded gas cost a few cents more. The legislature heard about this and outlawed self-service.

        As it happens, I was stationed in Oregon in 1977-80, after the law was passed but while leaded gas was still available. Some stations had older nozzles that were also of smaller diameter and would fit through the restrictor plates, and attendants would regularly offer to fill my new car, which had a cat, and the warning sticker, and the restrictor plate, with regular leaded gas. So I can see that they had good reason for the law, even if the law didn’t stop the behavior. But THEN, after you could no longer even FIND leaded gas, they never retired the law. So it BECAME a nanny state thing.

        Years later, when I moved back to Oregon, I was driving for a company that bought their fuel from Pacific Pride, which is a network of stations for commercial fleets, and being a fleet driver somehow made me not a consumer, so I could pump gas myself there, but I had to get “training” before they could issue me a card. The training consisted of reading a pamphlet that had all of the same warnings that were posted on the pumps. I mean, literally, word for word.

        We did have a temporary moratorium on this during the first corona virus outbreak, to minimize contact between customers and attendants, but now we’re back to no self-service. It was funny to watch, because many Oregonians had never pumped their own gas before.

    1. Another thing is where they retrofit older pumps with touchscreens, but don’t quite update the user interface, which means some of the selections you do have to be done by pressing the screen, and others from the buttons by the PIN pad, like selecting the number of the pump you want to use, and they don’t tell you whether to press the number on the pad or on the screen, so people just stand there scratching their heads wondering why nothing is happening.

  3. Well…

    The pressure is actually lowest in the throat of the venturi, not after. Since the mass flow through the tube is constant, the velocity at the smallest part of the throat is highest, leading to the lowest static pressure at that point. (Bernoulli’s principle.)

    Some old aircraft have an external venturi tube that’s used to power some instruments via the air pressure differential created by the tube.

    But nice to see the basic principle of the shutoff explained, anyway.

    1. A pitot tube which feeds the air speed indicator. They are notorious for freezing shut with ice, therefore most have heaters. Mine had a spider who crawled around the pitot tube cover which you put on while in the hangar and built a nest which didn’t cause problems until mostly down the runway on takeoff (yikes). Best of my knowledge all aircraft have them, not just old ones.

    1. Respond faster in what way? I used to work on a system that talked to gas pumps back in the late ’90s. (If your receipt has “TRACE” with a 4-digit number, it’s a version of that system. That’s a local transaction number to track the progress of the sale. Also it ran on a 6809 back then and I loved getting paid to write 6809 assembly code!)

      First, the pump side and the card reader terminal side are completely separate on all four major brands of that day (which was collapsing to just Gilbarco and Wayne by the time I moved on). They don’t even use the same RS-485 comm links. The pump part controls anything to do with fuel flow and pricing and nothing else. Any slow response time would probably be due to waiting on hardware to reset, or talking to the credit card network. But I didn’t have much to do with the pump side of things. Also, very large sites only put 12-16 positions per RS-485 bus, at those 9600-ish baud rates you can’t keep up with more!

      The card reader part (Gilbarco CRIND/Wayne CAT) used an 8-bit CPU in those days of 1-4 line displays, but Gilbarco’s then-new terminal with the big color screen actually ran Linux, I know because I captured its boot sequence from a serial port.

      The dumbest thing was that a couple of times I got L3 support calls when the pump handle didn’t click off and the gas spilled over. At least I didn’t get any calls reporting a hose drive-off as a software bug! (Yeah, people do that, and there’s an auto-disconnect fixture up there.)

      Another weird incident was when I was at a site where we were testing cash acceptors. As I was about to leave, people started saying that the gas had stopped pumping! After about 15 mins of freaking out, it turned out that the low-grade tank was empty. The site used “blender” pumps to sell three grades from two tanks, and only premium would dispense. (I actually don’t remember if anyone tried mid-grade.) So I left a message with their contact to roll a tanker truck out, and left.

    2. Agreed–I don’t know why gas pump UI is so bad. They have the money to invest in color touchscreens, etc, but error messages and status updates are not manually dismissable–you have to wait like 10 seconds for them to go away. How about asking me if I want a receipt while I’m waiting for my tank to fill up, instead of after?

  4. The Bowser company went on to manufacture mechanical meters as well. The longest lasting design was a multiple piston arrangement with a swash plate. The plant where I worked used these up until about 1990. I don’t know whether they are still used in gas pumps. If it goes tick, tick, tick, it’s probably a bowser style meter.

    There are a surprising number of places where the electric pump is in the underground tank.

  5. Thx. Another piece of the world puzzle falls into place. I always was in the back of my mind to check up on ‘how’ the nozzle works…. but by the time I get home after fill-up, I forget about it…. Sometimes simple mechanical devices/sensors are the best. I wonder sometimes if we just ‘over complicate’ the solution to problems.

    1. What’s funny is that we tend to think of new technology as the only sophisticated technology. But before electronics made its way into consumer products, there were a lot of very clever mechanical devices in the world, because there was no other option. This has been dumbed-down substantially, because electronics is almost always cheaper than mechanical devices, so most mechanical devices are made as simply as possible, leaving the tricky job of controlling them to microcontrollers. As a result, we don’t see a lot of complex mechanical devices these days. But just take a look at a 4-barrel carburetor or a mechanical fuel injection system from the 1950s sometime!

  6. One thing to note, the way this system is designed, you end up with a 1/2 a gallon of the other guy’s fuel. So, if you are filling up a gallon can with 91/93 octane fuel, you are likely not getting more then a 1/2 a gallon of 91/93 octane. Which is why I usually fill 4-5 gallon cans with 91/93 octane or pump first into my truck before filling a small can.

    1. Yes, well, I’ve heard reports that adding ethanol to gasoline reduces your mileage by up to 20%. Which would require that ethanol be a fire retardant, since they usually add no more than 10% ethanol into the mix.

  7. In 1980, I lived on the DelMarVa peninsula, in a mobile home that had a kerosene heater, so I had to buy kerosene, which I usually did at one of the local Ma-and-Pa grocery stores. They had a hand-cranked pump inside the store for this, that worked like the Bowser pump – it pumped kerosene into a glass bowl, and that would then drain into my 5-gallon can. These same stores also sold bologna by the slice, and would slice it right there at the cash register. And to be clear, this was 1980, not 1940.

  8. Thanks for the memories. My first design out of graduate school was the first electronic chemical additive controller for petroleum. See patent 5222027, The design used an Intel 80188 (‘186 for embedded designs), with 64K and a beautiful blue florescent graphical LCD screen. Quite novel for 1994. I spent days/weeks debugging at an Atlanta terminal (where the tankers fill-up). Aaah, I can still smell the fumes! Excellent article.

  9. Interesting! I don’t think this “blended” thing has ever been an option in the U.K. We just got lead, no lead, or diesel. Recently we’ve had “premium” options appear, but no mix-grades. The mind boggles at up to 5 grades being on sale!

    1. yes this is whole grade madness in US where you have 5 different blend with only 1 grade difference between them.
      An the little known fact that the higher the grade, the higher the consumption is…

      1. Are you sure higher grade = higher consumption? I thought modern cars with knock sensing etc. could usefully use the higher octane rating to run more efficiently (that’s the selling point of the high-grade fuels sold in the UK/EU) thus saving the extra cost.

        The whole 5 grades thing seems to be uniquely American, I’ve only seen similar in Russia where the grades run from premium if you’re very lucky, through regular (still quite decadent) down to “has sticks floating in it” 62-octane for the toothless old dude in the village to run his Soviet tractor on.

        1. Higher grade: lower density fuel so lower specific energy per volume
          Take diesel for example, it has way higher density than gasoline, but only around 25 octane rating.
          Most people think higher octane mean higher power or higher mpg, which is completely false.
          Some high performance motors need high octane to properly work (most direct injection ones), but it doesn’t mean they will have better mpg with higher than specified octane rating.

      2. In my experience it is just the other way round. I used to drive a TT. Two litre turbo engine, took “super” fuel as it is called here (98 octane) and could also run on regular (95), but at cost of some power loss. I usually got 640 km (400 miles) out of 50-52 litres (13.7 US gallon). On a trip to Sweden I stopped in Denmark to fill up with 101 octane and got 740 kilometers (462 miles) out of 54 litres (14.3 gallon).
        And I saw something about paying 4$ a gallon in the comments here, we pay $6,92 per gallon, which at the moment is low. It has been at $8.25.
        On a holiday in Oman I payed around a dollar per gallon, with the pump attendant mentioning that this was expensive, as in neighbouring Saudi Arabia it was a lot cheaper.

  10. You left out the most sophisticated part of the system – the mechanical analog computer that used to be driven by that flow meter, to keep a running total of both the flow and the price. Of course, no new pumps use those, but any time you see a pump with mechanical counters showing the price, there’s an analog computer behind that.

  11. In response to a few of the comments above…

    Virtually all new gas dispensers are blenders, which use the high octane grade and the low octane grade to produce the middle blended grade. On site blending also takes place with biodiesel at most large truck stops, but that doesn’t take place at the dispenser; that’s happening either underground by the tanks or in an above ground shed located in the tank area.
    The processing power of dispenser electronics is going up rapidly, mostly driven by newer IT security requirements to keep PIN and card information secure. Modern dispensers have their own internal network with outward facing IP addresses to provide high speed card processing at the pumps.
    Yeah, the media on the tv screens is annoying but they’ve figured out how to make money off that advertising so it’s not going away.
    Lots of safety features at the pumps…crash valves at ground level that snap shut to prevent flow should a collision occur, Intrinsically Safe electronic controls that prevent sparks (prevent igniting vapors), etc

  12. Just a short video over a venturi in a handle does not doe a gas station justice.
    Just the handle alone has some 10 safety related features, from stopping the flow when you let it fall out of your hands, and a valve that prevents people from draining the whole hose while nobody is looking just to name a few.

    Then there is the pump itself. Highly flammable liquids and electricity do not mix well, and yet it’s done in those things, but with lots of safety features. One of them is a vacuum pump to prevent vapours from building up, and lots of other features too. On top of the safety features there is the payment side, which needs calibrated and fairly accurate measurement of volume and price calculation.

    And even under the ground there is a load of safety features. Separate mechanisms are in place for metering the gasoline level and for preventing the tank from being overfilled. and on top of that there are other safety features such as double walled tanks with an (air) over pressure and metering, that gives an alarm if either the inner or outer tank starts leaking.

  13. Even the writer is confused about switch in the hall. It’s actually a 3 way switch at the ends. A 2 way switch is technically all switches that have 2 positions, up or down.
    The 3 way switch redirects where the electricity will travel to. Not actually on or off.
    That’s also the reason why 3 way switches don’t have labels of off or on printed on them.

    1. Okay, but a) the current through one of these switches is directed one of two ways, b) in a system using two if these switches, there are four possible states, so by your argument it should be “four way”, c) what are the three ways these can be set?

      And yes, I’m just messing with you. But explain this: I’ve seen “four way” used to describe circuits that have three switches.

      To me, three-way switches are the ones on lamps that have a ring terminal for dual filament bulbs, because of the three brightness settings. But then, even THOSE are four-way, since “off” is a brightness as well.

  14. Remembering the variable blend pumps are just youngsters. I remember when kerosene and white gas were dispensed by pumps at a different fuel island. Today they call white gas camp stove fuel.

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