Gas Pumps

Announcer: Go behind the wheel, under the hood, and beyond with CarStuff from

Scott Benjamin: Welcome to CarStuff. I'm Scott Benjamin, the auto editor here at

Ben Bowlin: My name is Ben Bowlin. I write some videos for the same website.

Scott Benjamin: How are you doing, Ben?

Ben Bowlin: Doing well, my friend. How are you?

Scott Benjamin: I'm okay. I'm a little more nasally than usual, if you can imagine that.

Ben Bowlin: Are you feeling a little under the weather?

Scott Benjamin: A little bit of a late summer cold, I guess, early fall cold, I guess you'd call it at this point, but I'm okay.

Ben Bowlin: Well, it's stylish. It's a good look for this time of year.

Scott Benjamin: Yeah, thanks. I appreciate it.

Ben Bowlin: You're kind of on the forefront -

Scott Benjamin: Can you see my swollen sinuses? I can't imagine. They feel like you can see them.

Ben Bowlin: You know, now that I'm seeing you in the studio you look normal, but now that I'm listening, I do hear just a little bit of a voice change.

Scott Benjamin: Yeah, a little bit. Not much. A little deeper. I like to hum to myself when I'm like this, like hm, hm, hm, hm. That was like - what is the name of those? Crash Test Dummies.

Ben Bowlin: Oh. "Once there was this boy who" -

Scott Benjamin: Yeah. That's what it is.

Ben Bowlin: Yeah, I remember that song.

Scott Benjamin: You know what? One thing - I'm going to make a wild guess here - you're from the South, right?

Ben Bowlin: Yes.

Scott Benjamin: Tennessee?Ben Bowlin:

YesScott Benjamin: I'm going to guess that you've been to some of these smaller towns, just in the hollers I guess, and I've traveled through there. I have relatives from that part of the world, and I know that up until very recently, even traveling, you'll find gas stations that have older gas pumps.

Ben Bowlin: Oh, yeah, definitely.

Scott Benjamin: And I'm not talking like the glass top with the liquid that you can see inside or anything like that. You do see those, but they're just abandoned. I'm talking about the type that have just the rotating numbers.

Ben Bowlin: Yes.

Scott Benjamin: So you probably remember these, r ight?

Ben Bowlin: Are you talking about the rotating - the way that an old school mechanical odometer would work or something?

Scott Benjamin: Yes. That's exactly. You remember that, right?

Ben Bowlin: Yes.

Scott Benjamin: Now, you're not very old?

Ben Bowlin: No.

Scott Benjamin: Well, those are from like the 1960s, 1970s.

Ben Bowlin: Early '70s.

Scott Benjamin: Early '70s because later, they went to - well, they had the digital readouts, and now they have digital readouts that are run by computer systems. It gets ridiculously advanced now, where they're showing advertisements and everything, and there's audio involved. But I remember going through the South and actually maybe not even in the South, but as far south as maybe Indiana, and seeing these pumps that had the rotating numbers.I thought those are pretty old. I started to look into the age of these things, and of course it's from the '60s and '70s. Going prior to that, you go back all the way to the beginning of the automobile, you find things like hand pumps that are purely mechanical. There's nothing electrical to them at all.

Ben Bowlin: Like hand-cranked gas systems?

Scott Benjamin: Yeah, exactly, hand-cranked gas systems that draw from a larger tank, but you see reservoirs in the top that you can measure it out. Just incredibly old systems, and people really get into collecting and all that, but I'm kind of interested in the newer stuff, the newer technology now. You know a little bit about this, right? You've been reading up on this?

Ben Bowlin: Yeah, I've been reading a little bit about gas pumps. I guess what we should do first is let's talk about just how a gas pump works. For a gas pump to be useful, you need to assume three, maybe four things - a car, gas, a gas pump, and then maybe, possibly, money to buy gas.

Scott Benjamin: Possibly.

Ben Bowlin: Yeah. So what exactly do these things do here? Maybe I'll start with an anecdote, Scott. In one of these hollers, where my family is from, there was this old skin flint, miserly dude who had this gas station and he had the regular and the high test, and this being a pretty depressed economy at the time, people try to get by just on the regular whatevers.Every so often, there would be some out of town, fancy person, who had to have the high test and sure enough, when that place burned down and the bulldozers came to clear out the area, they found out that those two pumps were just coming from the same tank.

Scott Benjamin: One tank?

Ben Bowlin: One tank. There was no difference. It was the same gas. The difference being the price at the pump. And we've heard these stories before, right? So the reason we've heard them before is because occasionally these things do happen. So when you have gas sold at a gas station, it's stored in these underground tanks, and this could be thousands and thousands of gallons of gas.

Scott Benjamin: Tanks plural, though?

Ben Bowlin: Yes. That's the way it's supposed to be.

Scott Benjamin: More than the one like the guy in your holler story.

Ben Bowlin: Yeah, not that guy. Different time.

Scott Benjamin: Yeah, I understand.

Ben Bowlin: So typically, these are divided by octane rating into three groups, and we've talked a little bit about octane rating on this podcast.

Scott Benjamin: Yeah, we've covered that.

Ben Bowlin: So tune into that episode if you'd like to learn more.

Scott Benjamin: Nice plug.

Ben Bowlin: Right. Thank you. And then how do we get the gas from the tank into your car? We use pumps. There are two types - there's a submersible pump or a suction pump, and I'm getting everybody - if I sound particular intelligent today, I'm getting all of this from an article called, "How Gas Pumps Work."

Scott Benjamin: Oh, Ben, don't short sell yourself. You're always intelligent.

Ben Bowlin: Ah, shucks.

Scott Benjamin: Even more so than when you're reading.

Ben Bowlin: Oh, thank you.

Scott Benjamin: Wait - did that make sense?

Ben Bowlin: Not really.

Scott Benjamin: Pass you in the hallway, you always have something intelligent to say.

Ben Bowlin: I work on it before I leave my desk.

Scott Benjamin: So chin up.

Ben Bowlin: It's true, though. All right. So a submersible pump is submerged below the surface of the gas.

Scott Benjamin: That makes sense.

Ben Bowlin: Yeah, so it uses kind of a propeller thing, an impeller if you will, to move the fuel upward. As this impeller is turning, it pushes the water the way that a fan blade turning pushes air.

Scott Benjamin: Pushes the gas?

Ben Bowlin: Pushes the gas the way a fan pushes air.

Scott Benjamin: Got it.

Ben Bowlin: And the suction pump does what it says - it uses suction or unequal pressure, so a motor above the fluid level removes air from a pipe, decreasing air pressure above the gas, and it keeps removing it until it ends up sucking the gas - wait, hang on. Let me not confuse myself. Until the weight of the surrounding air that is sucking out forces the gas inside the pipe upward even as gravity is pushing it down.

Scott Benjamin: So this is like an unequal pressure thing that forces the fluid up?

Ben Bowlin: Exactly.

Scott Benjamin: You know what? I know how to do this. I've mistakenly found out how to do this when I was a kid.

Ben Bowlin: How so?

Scott Benjamin: Juice box. You ever make the mistake of blowing air into a juice box?

Ben Bowlin: Oh, yeah.

Scott Benjamin: Oh, my gosh, what a mess.

Ben Bowlin: Good point because it comes back after you blow.

Scott Benjamin: It comes right back out. It usually goes all over your shirt, so don't try it, but it's no fun. Anyway, that's about the best I've got that can -

Ben Bowlin: Actually, that's a great example of unequal pressure.

Scott Benjamin: Yeah, I've recently experienced it again because you can't resist when something like that -

Ben Bowlin: Well, when the chance comes up.

Scott Benjamin: I know.

Ben Bowlin: Juice boxes don't come up that much anymore.

Scott Benjamin: No. A lot less dangerous than gasoline!

Ben Bowlin: Yes. And so we have to have a way to stop these pumps, right, before they just spew gas everywhere.

Scott Benjamin: Oh, sure, like the garden hose.

Ben Bowlin: Like a garden hose, sure. So we have some valves there to stop the gasoline from going everywhere and flooding the world. So there's a check valve and it's located inside the pipe, but it's above the gas, and it makes a seal above the gasoline. This is kind of used to hold the gas inside the pipe, but also to sort of - well, they call it "priming the pump" because the gas is still there inside the nozzle.

Scott Benjamin: Ah, maintains the pressure.

Ben Bowlin: Yeah. Precisely.

Scott Benjamin: Okay, I got it. Yeah, you've got the primary shutoff with your hand, right? That's where you stop the flow, really, but what's going on behind the scene is that further down the tube, so that the gas doesn't just flow all the way back down into the tank, the check valve stops that from happening and it keeps the gasoline ready to go, so it's there at a moment's notice, right?

Ben Bowlin: Yes.

Scott Benjamin: That's, I guess, the way I think of a check valve is something that blocks the flow because I've dealt with well systems before.

Ben Bowlin: It's similar.

Scott Benjamin: Very similar, yeah, so you don't have to prime that well system every time, unless you have a bad check valve and that's trouble, also.

Ben Bowlin: Well, if you think about it, though, the pause that it would take for it to come back up from the tank, in my opinion, is not that long.

Scott Benjamin: Oh, I think it would be a long time.

Ben Bowlin: It's like 10-20 seconds.

Scott Benjamin: Wouldn't it be longer the more fuel has gone from - especially in the type that you're talking about with the draw up, I guess. What was that? Not the submersible, but the other one.

Ben Bowlin: The suction.

Scott Benjamin: The suction tube. That would take a long time because you'd have to pump all the air out of the system. Those are giant tanks.

Ben Bowlin: Touché. Yeah, good point.

Scott Benjamin: I think the other type might be a little faster.

Ben Bowlin: But still, there's a wait.

Scott Benjamin: And it would be a wait, and it would be several seconds, I think. You're probably right, though. Negligible, I guess, on the first type. The other type - I keep forgetting the type. Not submersible.

Ben Bowlin: Oh, suction.

Scott Benjamin: Suction. I'll get that in my head. Suction.

Ben Bowlin: It's because they both start with an "s." You were right, though, when you talked about how the real point, the first point to stem the flow of the gas should be the driver's hand or whoever's pumping the gas. One thing that's kind of weird in Tennessee, they still have full service for a long time.

Scott Benjamin: You know what? You just reminded me. There are a few places still in the United States that are full service.

Ben Bowlin: Like on the Jersey turnpike you'll find some.

Scott Benjamin: You're exactly right, but what's weird about this, is I've been to New Jersey before. I went to Atlantic City a long time ago, and I swear I pumped my own gas, but maybe I was just across the border. I think we've talked about this.

Ben Bowlin: We have.

Scott Benjamin: I thought I pumped my own gas there.

Ben Bowlin: I think maybe you stole gas, bro.

Scott Benjamin: No, I don't think so. I paid for sure, so I had to have been on some weird, jagged border where I thought I was in New Jersey and I wasn't.

Ben Bowlin: But that's the law, right? All New Jersey is full service?

Scott Benjamin: It is, apparently, yeah. I think there are other states that are like that, as well. You'll still find that full service in small towns. I've seen that in little, tiny towns, real small, and you just reminded me of something.

Ben Bowlin: What?

Scott Benjamin: This is from a long time ago. I apologize on one of the details. I don't know one of the details in this.

Ben Bowlin: I gotcha.

Scott Benjamin: I don't remember if this was my uncle - this is on my dad's side, okay? I don't know if it was my uncle or my grandmother who did this, but back in the early '60s, I guess, early to late '60s, small town in Indiana, full service gas station, not because it was a law, but because that's what they did. They'd check your oil and that type of thing, right? I guess the end of the procedure, when you were done with eve rything, is when you pay the person. They handed you back your change.I'm going to say it was my uncle because he was a new driver at the time, so I think it was him, drove off from the gas station with the pump still in the filler. It didn't like blow up or anything. I think there was a fire. There was damage, but because this was before the days of the check valve, you didn't have to have this. They had them, but you didn't have to have them installed. So there was a fire, there was a big incident, I know, and there were damages. They didn't have to pay them because as it turned out, the transaction had occurred, where the money had gone back and forth. If it had not been for that, my grandparents would have had to buy a gas station pretty much.

Ben Bowlin: Wow. I'm glad they lucked out.

Scott Benjamin: That was a long time ago, yeah.

Ben Bowlin: Pay first.

Scott Benjamin: I don't remember if it was my grandmother or if it was my uncle. I'll have to investigate that.

Ben Bowlin: And get back to us.

Scott Benjamin: Yeah, exactly.

Ben Bowlin: Hey, here's one. We should answer this before we get to gas pumps in the future. This is a question that people wonder more so than you think - how does the gas pump know when your car is full?

Scott Benjamin: Ah, good one.

Ben Bowlin: Because it's at different times different levels, for every vehicle and every driver.

Scott Benjamin: Sure. You can't just say - well, other than getting a prepay, you can't say, "I need 10 gallons," or $10.00 or whatever you want to do. So how does it do it?

Ben Bowlin: Well, let's talk about our good friends the flow meter. So as gas passes through the control valve that regulates its speed, it uses this sort of plastic diaphragm that gets squeezed more and more tightly into the pipe as the flow increases.Stay with me here on this one. It always leaves just enough room for the proper amount of gas to get through, so if you've set a predetermined amount of gas to be pumped, the flow will slow down as you approach this limit, which is like what happens when you go into the service station and you say, "Give me $10.00 on pump number three," or whatever.So this pipe also has the actual flow meter, an iron and sometimes aluminum chamber - I guess now, it would be aluminum, sometimes iron chamber - containing gears and a rotor that ticks off units of gas as they pass through, so it's keeping count the way - do you ever see those people who walk around with pedometers to count their footsteps?

Scott Benjamin: Yes.

Ben Bowlin: Kind of like that. It measures a tenth of a gallon, and so as the temperature of the gas changes, the density of the gas can change, which can cause an error in the measurement.

Scott Benjamin: Ah ha, which gets to the point where I wonder am I really getting a gallon's worth of gas when I buy a gallon's worth of gas?

Ben Bowlin: You should be, theoretically, if you have a modern gas pump that has a computer system because it is supposed to compensate for this.

Scott Benjamin: So it adjusts to the temperature?

Ben Bowlin: Theoretically, again. I just keep thinking about that one guy who had the one tank and two pumps.

Scott Benjamin: Well, I've got something to say about that in a moment. So this thing adjusts, it keeps the flow, it knows the temperature, it knows how the gas is reacting to the outside temperature, how it's reacting to being pumped through the system and what it's going to be like when it gets to the end of the system, how much to allow to pass through, right?

Ben Bowlin: Yes. That's how it counts, and then there's the blend valve that also - am I reading your mind?

Scott Benjamin: You are, but go ahead.

Ben Bowlin: No, no, you do it.

Scott Benjamin: Well, this is the thing - the blend valve - this was probably the most interesting part of this article to me, just to me. I thought that for whatever reason, for many, many years, I thought that there were three grades of gasoline, there's going to be three tanks underneath the ground. Like you were saying with the one tank, right? That's a problem.If there's one tank that it's drawing from and it's giving both premium unleaded and regular unleaded, that's a problem. If you have two tanks, just a minimum of two tanks, you're able to do that. And I'm not just saying that there's premium and there's regular unleaded - you could do any number of octane levels with only two tanks.

Ben Bowlin: By mixing the two, right?

Scott Benjamin: Exactly, with the blend valve or the mixing valve. What do we call that thing? I've got it right here. I think it's called the blend valve. It mixes it right at the pump. It doesn't do it underground. It's not something that the guy that pumps the gasoline into the ground is doing. He's not measuring out how much he wants in each one. Well, he is, but he's not mixing them into some big concoction, saying 10 gallons of this, 20 gallons of that.

Ben Bowlin: Better mix up some midgrade before bedtime.

Scott Benjamin: Something like that, yeah. With a minimum of two tanks, you can get the highest octane; you can get the lowest octane that's in those tanks, of course.

Ben Bowlin: So 89 to 93 or whatever.

Scott Benjamin: Yeah, just by going straight 93 octane, straight 87 octane, and you can do anything in between using this mixing valve, which is just a simple mechanical thing that opens up. It can adjust, and it's just one moving part. I think the example in the article is if it's 90 percent open on the high test and 10 percent open on the other side, or it can adjust to 80/20 or 50/50 or 60/40 - anything that equals 100 - that moveable valve is what really gives you the octane level that you're seeking.

Ben Bowlin: The point we're trying to make here is it's not always four tanks under there. If they have diesel it'll be three tanks, probably.

Scott Benjamin: And I would guess if you have E-85 ethanol, I would think that they're going to have to have a separate tank for that.

Ben Bowlin: Which is happening more and more now?

Scott Benjamin: And of course, there's kerosene and there's different grades of diesel. I don't know how they do that, but we'll have to dig into that.

Ben Bowlin: I have to go on a tangent. I know this is weird, but this is something that kind of bothers me. I want to talk to you, the guru of all things automotive, about this.

Scott Benjamin: Oh, no.

Ben Bowlin: Why oh why do we insist on still saying "unleaded" gasoline? Where is the one guy still selling gasoline with lead in it?

Scott Benjamin: All right. I've worked for landscaping companies in the past. We had several machines, and I mean big, big trucks that took leaded gasoline. You had to buy a special mixture. You've probably seen these in the auto parts store. It's a plastic container, usually pretty large, really, maybe a liter or so, and it has a cup at the top and you squeeze fluid up into the cup to measure it out?

Ben Bowlin: Yes.

Scott Benjamin: And you pour that into your gas tank. It's a lead additive. It's very dangerous stuff.

Ben Bowlin: Seems like it.

Scott Benjamin: You add it into the unleaded fuel that you pump in at the pump, and that's how you keep these older machines still going. It all has to do with the seals, and its internal parts of your engine that require that lead for lubrication and for keeping them the right softness or hardness. That's why you still hear people say "unleaded" gasoline, which really it's just - at this point, you're just getting gasoline.

Ben Bowlin: All gasoline is unleaded, though. It bothers me.

Scott Benjamin: Yeah, I know.

Ben Bowlin: How much money could we save, I guess, on the cost of paint by not putting unleaded? It's like "drug-free school zone." It gets me. Where's the school where all these kids are doing drugs?

Scott Benjamin: I understand what you're saying, but there are machines out there that still require lead fuel. Very few, probably. You're talking mostly like farm implements and things like that that are just old, old engines, but it's required for them and that's why we're going to hang onto that type of stuff for a while.

Ben Bowlin: We're probably going to keep that label long after those vehicles.

Scott Benjamin: Yeah.

Ben Bowlin: Okay, so when you put the gas pump - you've pumped your gas, and when you put it back, it automatically shuts off the dispenser using a switch. Now, these switches are probably familiar to most people in my generation. As I was growing up, we always had the mechanical switches that you actually push the switch up when it's time for you to pump gas; you push it down -

Scott Benjamin: They're still around.

Ben Bowlin: Or something like that. They are still around.

Scott Benjamin: Just a few.

Ben Bowlin: Are we getting old?

Scott Benjamin: Yeah, we are. Most of them - you know what? It's the same exact thing that's operated by the nozzle when you put it in the pump. That's all. It's the exact same thing. It just takes your hands out of the procedure, which helps.

Ben Bowlin: And seems kind of fancy.

Scott Benjamin: Well yeah, I guess, but you don't have to get gasoline all over your hands.

Ben Bowlin: So what a long, convoluted answer I gave you, my friend, when you said, "Let's talk about the gas pumps of the future," and I went on like a 20-minute rip about how they work.

Scott Benjamin: I know, and I intro'd with that whole thing about the history of them and everything, but we didn't really even get much into the history of the gas pumps.

Ben Bowlin: We should do the history.

Scott Benjamin: Because I really like the old gas pumps, and I know they are highly collectible. A lot of people are really into these things - make, model, the advertising that's on them, the type of pump they are, the era that they come from. I think there's a lot to talk about there. The restoration of these things because they're still out there, and they're still hanging around and I know a lot of them are just decoration at this point, but the restored ones may end up in someone's home or garage, or even at a gas station outside as a display.

Ben Bowlin: And people steal some of the old ones becaus e they are the kind of things where if you paint them and fix them up a little, you can sell them.

Scott Benjamin: They're very valuable.

Ben Bowlin: So people have been taking them.

Scott Benjamin: Yeah, you're right. You're right. So I bet some of the ones that did exist at these old, broken down gas stations, they're owned by somebody. Somebody owns that property still. I bet a lot of them are disappearing. I bet you're right.

Ben Bowlin: It's true.

Scott Benjamin: That's about all I got, man.

Ben Bowlin: That's all you got?

Scott Benjamin: Yeah, that's about all I've got. As far as gas pumps and the new stuff, like I said, I do want to talk about old gas pumps someday, so look forward to that.

Ben Bowlin: Oh, so we're advertising? We're cheesing a little bit of a future episode.

Scott Benjamin: I think so.

Ben Bowlin: Yeah, there's so much in there. I'm sorry, man. I didn't mean to leave you hanging. I thought you were about to go on it.

Scott Benjamin: No, no. I'm done.

Ben Bowlin: Okay, story for another day.

Scott Benjamin: We'll hang onto it for later.

Ben Bowlin: We'll hang onto it.

Scott Benjamin: And I'll get the scoop if that was my uncle or my grandmother. The gas station fire!

Ben Bowlin: All right. That'll be your homework. My homework will be not to be involved in an accident, and I think I can get it. Knock on wood, right? So in the meantime, while we head out to take care of these things, why don't you guys take a second and give us your opinion about gas pumps, not just how they work, but the history or the future of them and what do you think about those ethanol pumps? I've never really worked with one.

Scott Benjamin: You know I've seen one.

Ben Bowlin: You've seen one?

Scott Benjamin: One.

Ben Bowlin: Just the one?

Scott Benjamin: Just one. That's it.

Ben Bowlin: Well, we live here in Georgia.

Scott Benjamin: I know. I bet the closer to the Midwest we get, if we go up a little bit further north, we'll find some.

Ben Bowlin: So guys can hit us up on CarStuff@Facebook, CarStuff@Twitter. You can always check in with our blog. You can look at the article that we're raving about by Christopher Lampton. They're on our website, "How Gas Pumps Work," and if we somehow did not cover what you really wanted to hear about, please send us an email at -

Scott Benjamin:

Announcer: For more on this and thousands of other topics, visit The HowStuffWorks iPhone app is coming soon. Get access to our content in a new way - articles, videos, and more all on the go. Check out the latest podcasts and blog post, and see what we're saying on Facebook and Twitter. Coming soon to iTunes.