[NA-ish] Probably a stupid question, but...

ArrowFlyer86

ArrowFlyer86

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I have many recurring questions that are probably really dumb and individually definitely not worthy of a thread, so I'm going to create a thread to house them all and periodically add to it... Feel free to ask your own...

First question...
Why is a car gas pump so much slower than an air aircraft one? When I use self-serve fuel for the airplane, I'd estimate I can fill up 25gal for the wing in about 30 seconds if I left it rip (and don't care about spilling).

Meanwhile.. In my Elantra with a 12.4gal tank, it takes a solid 1-1.5 minutes to fill. Half the gas and much longer fill time..

I know it's typically a somewhat wider diameter hose on the the avgas pump, but the nozzles on the two looks like a similar-ish diameter, which I would think is the limiting factor for flow rate? So why is one so much faster than the other?
 
It'd be cool if car gas tanks could report to the pump its current fuel level so the pump could bulk-pump quickly to 80% then taper off slowly to limit spills. Like EVs do :)

I do that by "ear" on mine so I have to assume we could do this with some clever code and a microphone.
 
schmookeeg said:
It'd be cool if car gas tanks could report to the pump its current fuel level so the pump could bulk-pump quickly to 80% then taper off slowly to limit spills. Like EVs do :)

I do that by "ear" on mine so I have to assume we could do this with some clever code and a microphone.
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Oh man, I forget if it was the last truck, or the one before, but it would start "overfilling" at half full. The nozzle had to be absolutely perfect or the auto-shutoff would kick in.
 
At the car gas pump, I just lock the trigger and it stops at some point I can’t add any more without causing an overflow.

At the airplane pump, I carefully balance on a ladder and manually decide when to stop.

Why can’t I have the same trigger on the 100LL pump/hose?
 
schmookeeg said:
It'd be cool if car gas tanks could report to the pump its current fuel level so the pump could bulk-pump quickly to 80% then taper off slowly to limit spills. Like EVs do :)

I do that by "ear" on mine so I have to assume we could do this with some clever code and a microphone.
Click to expand...
You do it by ear? You should probably share your research with this scientific body.
1745256915981.png
 
ArrowFlyer86 said:
You do it by ear? You should probably share your research with this scientific body
Click to expand...

Isn't that the same scientific body that spent years researching the Thermos bottle? They could not answer the age old question of how it keeps the hot things hot...yet, it keeps the cold things cold! But....how do it know?????
 
ArrowFlyer86 said:
I have many recurring questions that are probably really dumb and individually definitely not worthy of a thread, so I'm going to create a thread to house them all and periodically add to it... Feel free to ask your own...

First question...
Why is a car gas pump so much slower than an air aircraft one? When I use self-serve fuel for the airplane, I'd estimate I can fill up 25gal for the wing in about 30 seconds if I left it rip (and don't care about spilling).

Meanwhile.. In my Elantra with a 12.4gal tank, it takes a solid 1-1.5 minutes to fill. Half the gas and much longer fill time..

I know it's typically a somewhat wider diameter hose on the the avgas pump, but the nozzles on the two looks like a similar-ish diameter, which I would think is the limiting factor for flow rate? So why is one so much faster than the other?
Click to expand...

It seems to me that there is more back-pressure filling a car than filling the airplane. Isn't back-pressure how the nozzle "knows" to shutoff the flow?
 
There's all different sizes of pumps. Here at the farm I've got a 15 gal/min pump on the gas tank and 25gpm on the diesel. It also requires a bigger nozzle and hose. If you go to a truck stop, you'll find that the diesel pumps got the trucks are similar in size & speed to the pump at the airport.

Most cars are only taking 10-20 gallons, and you also have to accommodate motorcycles. The bigger nozzles are harder to stop for small amounts, and cars have limiters to limit the size of the nozzle anyway, for the same reason jet a nozzles have a duckbill that prevents putting it into an avgas tank.

Meanwhile semis and airplanes are taking 50-100 gallons, so a 10gpm flow rate would be tedious. I'd bet there's an SAE standard for fueling stations that describes all this. Maybe NFPA.

I don't know what kind of flow rates the central fill jet a trucks are pushing. 50gpm? 100?
 
EdFred said:
Oh man, I forget if it was the last truck, or the one before, but it would start "overfilling" at half full. The nozzle had to be absolutely perfect or the auto-shutoff would kick in.
Click to expand...
That's reason enough to sell the vehicle.

asicer said:
Does your state mandate the use of vapor recovery nozzles and hoses for automotive pumps?
Click to expand...
Great question, no idea!

Bob Noel said:
It seems to me that there is more back-pressure filling a car than filling the airplane. Isn't back-pressure how the nozzle "knows" to shutoff the flow?
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Hmm, that sounds scientific and correct...
With the airplane you're kinda just pouring it into a big empty container. The nozzle wouldn't get any backpressure right? At least for my aircraft. It's just a wide open inlet where fuel can go in and air can come out.
 
I think the center point refueling is 300+ gồm. But they have a 4 to 6 inch diameter hose. I know I've taken on 40,000 lbs in less than or right at 10 minutes, so about 3300 gallons or so.
 
asicer said:
Does your state mandate the use of vapor recovery nozzles and hoses for automotive pumps?
Click to expand...
Illinois does not. Some Chicago area counties may, but if they do, I haven't seen them.
 
ArrowFlyer86 said:
Why is a car gas pump so much slower than an air aircraft one?
Click to expand...
There's a lot more going on with a city-based vehicle refueling system in general than with an aircraft refueling system.

TCABM said:
Why can’t I have the same trigger on the 100LL pump/hose?
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They're available and have tried them before. But they tend to need more preventive mx than regular refuel nozzles and for the extra price not worth it.
 
Mikey52 said:
Slower pumps. They are set to about 12 gal per minute.
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The leaves more time for you to head inside and get that "cold pop" (thanks Sweet Brown) and hotdog that's been on the roller for 4 days.
I've seen it said that's where the money is vs. gas sales.
 
my class C motohome's gasoline tank is 55 gallons...I use the same slow pumps made for cars and motorcycles and 1 gallon lawn mower gas cans....
 
None of this is important.
What we should be rant-discussing is why so many operators can get away with pumps that promise, then fail to provide printed receipts!
I must have them for so many reasons.
Do they think I am really likely to buy any snacks or drinks if I have to storm inside, fume in line to get my receipt?
I just found a valid reason to block the pump while I go inside. (any other reason is annoyingly invalid)
 
Maybe an unreasonable concern, but it feels like the flow out of some nozzles could rip the bladder!
 
The last time I took a cross country trip in the Dodge diesel Ram (25+ years ago) I noticed that while some truck stops had gasoline fuel pumps, if you wanted diesel, you had to go to the pumps for the big rigs. Those were more like avgas dispensers. Actually, probably the same nozzles. Filled a 35 gallon tank in about ten seconds.
 
Sac Arrow said:
The last time I took a cross country trip in the Dodge diesel Ram (25+ years ago) I noticed that while some truck stops had gasoline fuel pumps, if you wanted diesel, you had to go to the pumps for the big rigs. Those were more like avgas dispensers. Actually, probably the same nozzles. Filled a 35 gallon tank in about ten seconds.
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At least in the years I was driving 15-25 years ago, the truck diesel pumps were bigger nozzles than avgas. In fact, I bet you could fit an avgas nozzle inside a truck diesel nozzle.

A box truck may only have a 40-gallon diesel tank, but over-the-road semi tanks are 200-300 gallons. Even with relay pumps (filling both sides simultaneously) it's not quick enough when you're getting paid by the mile.
 
It's a EPA thing. They restricted the flow of car gas years ago to try reduce over fills to protect the ozone.
 
flyingcheesehead said:
At least in the years I was driving 15-25 years ago, the truck diesel pumps were bigger nozzles than avgas. In fact, I bet you could fit an avgas nozzle inside a truck diesel nozzle.

A box truck may only have a 40-gallon diesel tank, but over-the-road semi tanks are 200-300 gallons. Even with relay pumps (filling both sides simultaneously) it's not quick enough when you're getting paid by the mile.
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Yup our RV has dual 100 gallon tanks, one inch nozzles are needed for trucks. Spilled diesel doesn't eat the ozone. Just pollutes the ground water.
 
Last edited:
So funny thing. I was out flying today and decided to stop for gas. I grounded the plane, swiped my card and dragged the hose out to the wing. As I pulled the trigger, I noticed that the grip felt different. Plus, the nozzle was curved and had a coil around the outlet. Yup, somebody put an automotive nozzle on the 100LL pump. And BAM, it stopped even though it was still below the tabs. I guess the auto-shutoff is still enabled.

Anyway, as I was pumping I counted 5 seconds per gallon (12 gallons per minute) if anybody is curious.
 
Gary Ward said:
It's a EPA thing. They restricted the flow of car gas years ago to try reduce over fills to protect the ozone.
Click to expand...
I think it’s been a slow step by step process starting in 1974 when they made the hole in the filler tanks smaller so leaded gas fill nozzles couldn’t be put into cars with catalytic converters and render them inoperable. The biggest change I noticed was a while ago when the price of gas spiked and all the gas stations around my area “upgraded” their pumps to smaller diameter hoses. I assumed at the time it was a subtle marketing ploy (the numbers weren’t spinning up so fast so the consumer didn’t notice as much). My gas v-10 3500 has big tanks and I run it almost dry then fill them, seems to run better that way (each batch is a bit different and takes a while for the computer to remap). I’ve gotten to the point now I just put in the hose, latching the nozzle, and read the news on my phone while it fills sitting in the cab, it’s going to take a while.
(And for the false “full” people, when it clicks off and clicks off like it’s full when it’s not, and you have to further slow your filling, the charcoal fuel vapor absorber is plugged up. Stop topping it off and let it rebalance, after a few tanks of gas it should fill normally again. Or you can take it to a shop, pay a few hundred bucks to get it replaced and have it do it again in a few months if you keep topping the tank off like in old school cars).
 
ArrowFlyer86 said:
Why is a car gas pump so much slower than an air aircraft one?
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You spend more time at the gas station that way. They play an ad at the pump and convince you to come inside and buy some overpriced item you don't need.
 
AV8R_87 said:
You spend more time at the gas station that way. They play an ad at the pump and convince you to come inside and buy some overpriced item you don't need.
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The first time I saw an ad playing at a gas pump, I stared in disbelief at what was undoubtedly the harbinger of the fall of our civilisation. Is nothing sacred? Can I not now even have that 30 seconds of zen-like mental disengagement as I watch numbers scroll ever upwards, bathed in gasoline fumes that tick a few minutes off my life? And why, back when I lived as a small boy on a small island and it was properly called "petrol", did it smell so good? And when did that change? And why? And who is responsible?
 
AvNavCom said:
The first time I saw an ad playing at a gas pump, I stared in disbelief at what was undoubtedly the harbinger of the fall of our civilisation.
Click to expand...
I punished that gas station chain by not buyng gas there. I even told the manager why I'd rather drive two miles to their competitor.
If more people did the same, that stupidity would stop.
 
Jim K said:
There's all different sizes of pumps. Here at the farm I've got a 15 gal/min pump on the gas tank and 25gpm on the diesel. It also requires a bigger nozzle and hose. If you go to a truck stop, you'll find that the diesel pumps got the trucks are similar in size & speed to the pump at the airport.

Most cars are only taking 10-20 gallons, and you also have to accommodate motorcycles. The bigger nozzles are harder to stop for small amounts, and cars have limiters to limit the size of the nozzle anyway, for the same reason jet a nozzles have a duckbill that prevents putting it into an avgas tank.

Meanwhile semis and airplanes are taking 50-100 gallons, so a 10gpm flow rate would be tedious. I'd bet there's an SAE standard for fueling stations that describes all this. Maybe NFPA.

I don't know what kind of flow rates the central fill jet a trucks are pushing. 50gpm? 100?
Click to expand...

Sac Arrow said:
The last time I took a cross country trip in the Dodge diesel Ram (25+ years ago) I noticed that while some truck stops had gasoline fuel pumps, if you wanted diesel, you had to go to the pumps for the big rigs. Those were more like avgas dispensers. Actually, probably the same nozzles. Filled a 35 gallon tank in about ten seconds.
Click to expand...
I believe there are some diesel nozzles at the big rig stations that won't fit in the hole that normal auto-diesel does. A common solution to that was to use tin snips to the fuel fill and enlarge the hole so that the semi-truck fuel nozzle could fit and you could take advantage of the higher flow rate at truck stops. My Excursion has that modification since it has a factory 44gal tank and the standard auto diesel pumps take quite a while to fill it up.
 
AvNavCom said:
The first time I saw an ad playing at a gas pump, I stared in disbelief at what was undoubtedly the harbinger of the fall of our civilisation. Is nothing sacred? Can I not now even have that 30 seconds of zen-like mental disengagement as I watch numbers scroll ever upwards, bathed in gasoline fumes that tick a few minutes off my life? And why, back when I lived as a small boy on a small island and it was properly called "petrol", did it smell so good? And when did that change? And why? And who is responsible?
Click to expand...
These questions sound like the musings of an old, nostalgic man. Wishing for the simpler times of our yesteryears when a man could pump his gas in peace :D
But yeah the BP station by me starts their ads almost right away, often with the most ridiculous videos: called "better together" (with some C-List celebrity whose best job prospects was making ****ty videos to annoy you at the gas pump)
 
The idiot marketeers will drive me (no pun) to the plug-in hybrid.

I've told various stations that I won't put up with the ads... but they don't care... I guess there are enough sheep in the world that it won't cost them a dime (or at least they won't notice).
 
This thread made me think of this. My gas station took it to a new level with these ads on the pump.
It's a mobil right by my home airport that advertises the happy hour at the bar/restaurant inside the gas station
Don't know how much of an alcoholic you have to be to stop off for gas and get tanked on $4 margaritas. But a new cross selling opportunity... I guess.

1745422830229.png
 
SoonerAviator said:
I believe there are some diesel nozzles at the big rig stations that won't fit in the hole that normal auto-diesel does. A common solution to that was to use tin snips to the fuel fill and enlarge the hole so that the semi-truck fuel nozzle could fit and you could take advantage of the higher flow rate at truck stops. My Excursion has that modification since it has a factory 44gal tank and the standard auto diesel pumps take quite a while to fill it up.
Click to expand...
Right. My '95 Ram had a hole that would work for the big rig nozzles.
 
Flatiowa said:
My gas v-10 3500 has big tanks and I run it almost dry then fill them, seems to run better that way (each batch is a bit different and takes a while for the computer to remap). I’ve gotten to the point now I just put in the hose, latching the nozzle, and read the news on my phone while it fills sitting in the cab, it’s going to take a while.
Click to expand...
1) With many vehicles, it is better to refuel at 1/4 to avoid issues with the in tank fuel pump over heating.

2) Getting back into your vehicle while fueling was found to be the cause of most of the gas station fueling fires, not cell phones. Getting in and out can build a static charge on your, so when you touch the nozzle, you get a spark, right there with gas vapors. Interestingly, what lead to figuring this out was that most gas station fires occurred with women. It seems women are more likely to get back in their cars while fueling.
 
Pinecone said:
1) With many vehicles, it is better to refuel at 1/4 to avoid issues with the in tank fuel pump over heating.

2) Getting back into your vehicle while fueling was found to be the cause of most of the gas station fueling fires, not cell phones. Getting in and out can build a static charge on your, so when you touch the nozzle, you get a spark, right there with gas vapors. Interestingly, what lead to figuring this out was that most gas station fires occurred with women. It seems women are more likely to get back in their cars while fueling.
Click to expand...
You know, I've heard that quoted many times but not sure how much data is really behind it. I almost put it in the realm of automotive folklore. The fuel pumps that are cooled that way are typically at the bottom of the fuel sump and would be submerged with a gallon or two of fuel in the tank. Many of the fuel pumps don't sit in the fuel at all unless you've got a full tank as the motor itself is the top and uses a pickup tube to draw from the bottom of the tank.

Example of modern fuel pump on F-150:
1745432974011.png
 
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