How does a gas pump know when your tank is full?

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[ARCHIVED THREAD] - How does a gas pump know when your tank is full?

Posted: 5/19/2005 5:33:18 PM EDT

How does a gas pump know when your tank is full? ...then it shuts off preventing spillover?

Posted: 5/19/2005 5:34:35 PM EDT

[#1]

pressure build up shuts off an eternal switch is my guess.

That or you only paid for $60 in gas.

SGat1r5

Posted: 5/19/2005 5:35:29 PM EDT

[#2]

A midget inside the pump station.

Thats all I can divulge at this time.

ETA Midget sounds funnier than dwarf

Posted: 5/19/2005 5:36:25 PM EDT

[#3]

Quoted:
A dwarf inside the pump station.

Thats all I can divulge at this time.

So THAT's where DoubleFeed lives!

Sgatr15

Posted: 5/19/2005 5:36:55 PM EDT

[#4]

Burning question I had.

Posted: 5/19/2005 5:38:10 PM EDT

[#5]

I have no knowledge of that, and if I did know about that, I cannot confirm nor deny that.

Posted: 5/19/2005 5:38:38 PM EDT

[#6]

The speed of the air displaced back out the tube I believe.

My .02

Posted: 5/19/2005 5:39:16 PM EDT

[#7]

Quoted:
pressure build up shuts off an eternal switch is my guess.

That or you only paid for $60 in gas.

SGat1r5

One that never goes bad.

Posted: 5/19/2005 5:40:12 PM EDT

[#8]

Quoted:
How does a gas pump know when your tank is full? ...then it shuts off preventing spillover?

You sure do come up with stupid shit!

Posted: 5/19/2005 5:43:02 PM EDT

[#9]

gas nozzles have sensors to detect rising liquid as a safty precaution

Posted: 5/19/2005 5:45:34 PM EDT

[#10]

From what I understand, the pumps have a vapor recovery system to vacuum out the evaporated gas from your tank as it fills with liquid. When the recovery hose takes more vacuum to draw vapor, it knows its hit liquid and cuts off.

Kharn

Posted: 5/19/2005 5:48:12 PM EDT

[#11]

Yahoodie tells it.

Posted: 5/19/2005 5:49:37 PM EDT

[#12]

Quoted:
From what I understand, the pumps have a vapor recovery system to vacuum out the evaporated gas from your tank as it fills with liquid. When the recovery hose takes more vacuum to draw vapor, it knows its hit liquid and cuts off.

Kharn

That makes perfect sense.
As the gas fills up the tank it would displace the gas vapors.
Those vapors need to go somewhere.

I wonder how many exploding smokers it took for them to come up with a system like you explained.

Posted: 5/19/2005 5:50:14 PM EDT

[#13]

Quoted:
Quoted:
A dwarf inside the pump station.

Thats all I can divulge at this time.

So THAT's where DoubleFeed lives!

Sgatr15

I live off of beer and and those wierd little cheesecake thingies, but I consume just below the "notice" threshold.

Posted: 5/19/2005 5:50:31 PM EDT

[#14]

When you fill your gas tank, some of the displaced air flows through the hole in the nozzle into the pipe. When the tank is full, the hole will be below the gasoline level and no air will pass through the pipe. A mechanical switch inside the nozzle detects when the flow of air stops and shuts off the gas.

You may have noticed that, after the pump shuts off, you can get more gas in your tank by pulling the nozzle out of the tank a bit. This is because you’re moving the position of the hole relative to the gas level and allowing the mechanical switch to reopen.

Posted: 5/19/2005 5:51:24 PM EDT

[#15]

Quoted:
Quoted:
pressure build up shuts off an eternal switch is my guess.

That or you only paid for $60 in gas.

SGat1r5

One that never goes bad.

Its a heavenly switch, made of gold.

Posted: 5/19/2005 5:53:30 PM EDT

[#16]

When your gas gauge reads empty, your tank is filled with air instead of fuel. As you add fuel, the air must move out of the tank to make way for the gas. Next time you fill your car at the gas station, take a look at the pump nozzle. You will find a hole about a half inch from the end of the nozzle. This hole is connected to a small pipe that travels through the nozzle to the handle.

When you fill your gas tank, some of the displaced air flows through the hole in the nozzle into the pipe. When the tank is full, the hole will be below the gasoline level and no air will pass through the pipe. A mechanical switch inside the nozzle detects when the flow of air stops and shuts off the gas.

You may have noticed that, after the pump shuts off, you can get more gas in your tank by pulling the nozzle out of the tank a bit. This is because you’re moving the position of the hole relative to the gas level and allowing the mechanical switch to reopen.

Posted: 5/19/2005 5:55:15 PM EDT

[#17]

Quoted:
When your gas gauge reads empty, your tank is filled with air instead of fuel. As you add fuel, the air must move out of the tank to make way for the gas. Next time you fill your car at the gas station, take a look at the pump nozzle. You will find a hole about a half inch from the end of the nozzle. This hole is connected to a small pipe that travels through the nozzle to the handle.

When you fill your gas tank, some of the displaced air flows through the hole in the nozzle into the pipe. When the tank is full, the hole will be below the gasoline level and no air will pass through the pipe. A mechanical switch inside the nozzle detects when the flow of air stops and shuts off the gas.

You may have noticed that, after the pump shuts off, you can get more gas in your tank by pulling the nozzle out of the tank a bit. This is because you’re moving the position of the hole relative to the gas level and allowing the mechanical switch to reopen.

looks like we both googled the same article....

Here's another explanation

In a gas pump handle you have two valves: the main valve, which is actuated by the oversize trigger you squeeze to make the gas flow, and the check valve, which lets gas flow out but won't let anything back in again, thus reducing fire hazard. In the seat of the check valve you have a little hole. To the backside of this hole is connected a Y-shaped tube. One branch of this tube runs down the nozzle and exits at the tip while the other runs back to a diaphragm connected to a release mechanism on the main valve. When you squeeze the gas pump trigger, gas running past the hole in the check valve sucks air out of the Y-shaped tube. (This is because of the Bernoulli principle: a moving stream of fluid tends to pull things in from the sides. Take my word for it.) As long the end of the Y-shaped tube exiting at the spout is unobstructed, air is simply pulled into the tube and nothing much else happens. However, as soon as the gas in your car's fill-up pipe gets high enough to cover the end of the tube, a partial vacuum is created therein, which yanks on the diaphragm, releases the main valve, and shuts off the gas. If the gas happens to be especially foamy one day, it may actuate the release mechanism prematurely, with the result that you end up with less than a full tank of gas.

Posted: 5/19/2005 5:57:21 PM EDT

[#18]

Quoted:
From what I understand, the pumps have a vapor recovery system to vacuum out the evaporated gas from your tank as it fills with liquid. When the recovery hose takes more vacuum to draw vapor, it knows its hit liquid and cuts off.

Kharn

Not all states' EPA's require vapor recovery. In fact, california was the only state between there and michigan that I filled up in that did have vapor recovery nozzles. All the other states I've been in don't have them.

If you look down the nozzle you'll see a tiny tube that goes to an opening on the side of the pipe. This small pipe does indeed sense the backpressure created by filling a tank, and trips the handle to stop pumping (the mechanism inside is very similar to a trigger/sear/hammer setup which is why regripping the handle keeps pumping).

Yeah, 5 years of pump jockeying. The amazing thing is that the station I worked at payed $80 per pump handle and $100+ for the hoses (vapor recovery in CA) between the handle and the quickrelease. I hate it when people drive off with the nozzle still in their tank. Stupid people.

ETA that my answer was without googling and I started before the copy/paste crowd up there started replying

Posted: 5/19/2005 6:01:19 PM EDT

[#19]

Quoted:
Quoted:
From what I understand, the pumps have a vapor recovery system to vacuum out the evaporated gas from your tank as it fills with liquid. When the recovery hose takes more vacuum to draw vapor, it knows its hit liquid and cuts off.

Kharn

Not all states' EPA's require vapor recovery. In fact, california was the only state between there and michigan that I filled up in that did have vapor recovery nozzles. All the other states I've been in don't have them.

If you look down the nozzle you'll see a tiny tube that goes to an opening on the side of the pipe. This small pipe does indeed sense the backpressure created by filling a tank, and trips the handle to stop pumping (the mechanism inside is very similar to a trigger/sear/hammer setup which is why regripping the handle keeps pumping).

Yeah, 5 years of pump jockeying. The amazing thing is that the station I worked at payed $80 per pump handle and $100+ for the hoses (vapor recovery in CA) between the handle and the quickrelease. I hate it when people drive off with the nozzle still in their tank. Stupid people.

ETA that my answer was without googling and I started before the copy/paste crowd up there started replying

Many states don't have the vapor recovery, none of them around here do.

Posted: 5/19/2005 6:03:57 PM EDT

[#20]

Quoted:
If the gas happens to be especially foamy one day, it may actuate the release mechanism prematurely, with the result that you end up with less than a full tank of gas.

This can also happen on vapor recovery systems when people 'top off' their gas tanks and force liquid gasoline back into the vapor part of the hose. Enough liquid fuel in the bottom of the hose and a pump will constantly shut off. One of my jobs was to empty the vapor hoses whenever they got too full. Regular, plus and supreme all went back into the regular underground tank. wheefun.

Posted: 5/19/2005 6:07:02 PM EDT

[#21]

lektricity

or maybe magic.

Posted: 5/19/2005 6:07:18 PM EDT

[#22]

Quoted:
When your gas gauge reads empty, your tank is filled with air instead of fuel. As you add fuel, the air must move out of the tank to make way for the gas. Next time you fill your car at the gas station, take a look at the pump nozzle. You will find a hole about a half inch from the end of the nozzle. This hole is connected to a small pipe that travels through the nozzle to the handle.

When you fill your gas tank, some of the displaced air flows through the hole in the nozzle into the pipe. When the tank is full, the hole will be below the gasoline level and no air will pass through the pipe. A mechanical switch inside the nozzle detects when the flow of air stops and shuts off the gas.

You may have noticed that, after the pump shuts off, you can get more gas in your tank by pulling the nozzle out of the tank a bit. This is because you’re moving the position of the hole relative to the gas level and allowing the mechanical switch to reopen.

NO, NO, NO, The person at the register has a chart that shows how much gas each model of car holds. When it gets close to full, they shut of the pump.

Maybe I don't know what I'm talk'n 'bout

Posted: 5/19/2005 6:10:28 PM EDT

[#23]

Quoted:
Quoted:
When your gas gauge reads empty, your tank is filled with air instead of fuel. As you add fuel, the air must move out of the tank to make way for the gas. Next time you fill your car at the gas station, take a look at the pump nozzle. You will find a hole about a half inch from the end of the nozzle. This hole is connected to a small pipe that travels through the nozzle to the handle.

When you fill your gas tank, some of the displaced air flows through the hole in the nozzle into the pipe. When the tank is full, the hole will be below the gasoline level and no air will pass through the pipe. A mechanical switch inside the nozzle detects when the flow of air stops and shuts off the gas.

You may have noticed that, after the pump shuts off, you can get more gas in your tank by pulling the nozzle out of the tank a bit. This is because you’re moving the position of the hole relative to the gas level and allowing the mechanical switch to reopen.

looks like we both googled the same article....

Here's another explanation

In a gas pump handle you have two valves: the main valve, which is actuated by the oversize trigger you squeeze to make the gas flow, and the check valve, which lets gas flow out but won't let anything back in again, thus reducing fire hazard. In the seat of the check valve you have a little hole. To the backside of this hole is connected a Y-shaped tube. One branch of this tube runs down the nozzle and exits at the tip while the other runs back to a diaphragm connected to a release mechanism on the main valve. When you squeeze the gas pump trigger, gas running past the hole in the check valve sucks air out of the Y-shaped tube. (This is because of the Bernoulli principle: a moving stream of fluid tends to pull things in from the sides. Take my word for it.) As long the end of the Y-shaped tube exiting at the spout is unobstructed, air is simply pulled into the tube and nothing much else happens. However, as soon as the gas in your car's fill-up pipe gets high enough to cover the end of the tube, a partial vacuum is created therein, which yanks on the diaphragm, releases the main valve, and shuts off the gas. If the gas happens to be especially foamy one day, it may actuate the release mechanism prematurely, with the result that you end up with less than a full tank of gas.

I wrote that one too!

Posted: 5/19/2005 6:11:16 PM EDT

[#24]

Quoted:
How does a gas pump know when your tank is full? ...then it shuts off preventing spillover?

The trunk monkey tells the pump when its full!

Posted: 5/19/2005 6:14:32 PM EDT

[#25]

Cool replies! it looks like there is alot of ways to get'er done.

I asked the question because im trying to find a better way to fill wine barrels. I would like to leave them un-attended because it takes about 15 minutes to fill a 60 gallon barrel..and if you are filling alot of barrels thats a whole DAY of sitting next to a barrel trying to guess when its full so it doesnt overflow...and when it does overflow it shoots wine all over the damn place.

the way we do it now is stick a long stainless pipe into the top of barrel and use the speed control of the wine pump to to turn it on and off to filll the barrel. the pipe has to extend all the way down to the bottom of the barrel into the liquid so that it doesnt aerate the wine.

any ideas for an auto shut off?

Posted: 5/19/2005 6:16:25 PM EDT

[#26]

Quoted:
lektricity

or maybe magic.

It's magic as AeroE said but he wasn't supposed to tell. I am calling for the immediate suspension of AeroE from the magicians guild. Turn in your rabbit and top hat immediately!

Posted: 5/19/2005 6:17:30 PM EDT

[#27]

Quoted:
From what I understand, the pumps have a vapor recovery system to vacuum out the evaporated gas from your tank as it fills with liquid. When the recovery hose takes more vacuum to draw vapor, it knows its hit liquid and cuts off.

Kharn

Correct.

I found this out the long way when I got to dissect a nozzle from a gas station in Berkeley that went out of business and donated a nozzle to the cause.

Posted: 5/19/2005 6:31:13 PM EDT

[#28]

Quoted:
Quoted:
If the gas happens to be especially foamy one day, it may actuate the release mechanism prematurely, with the result that you end up with less than a full tank of gas.

This can also happen on vapor recovery systems when people 'top off' their gas tanks and force liquid gasoline back into the vapor part of the hose. Enough liquid fuel in the bottom of the hose and a pump will constantly shut off. One of my jobs was to empty the vapor hoses whenever they got too full. Regular, plus and supreme all went back into the regular underground tank. wheefun.

doesnt suprise me since all the octane reading is what the minimum is.

but as for the shut off I always wondering about that. Hmm learn something new every day.

Posted: 5/19/2005 6:36:22 PM EDT

[#29]

A mechanical switch inside the nozzle detects when the flow of air stops and shuts off the gas.

OK, can anyone explain why early to late 80's Toyotas don't work well with that sensor? When I started working at my current job, we had a couple of early 1983 Toyota Celicas, six 1985 Toyota pickups, six late 80's Camry's, and three late 80's 4Runners. I also personally owned a Tercel and a Corolla from the same time period. On all of them, the sensor on the nozzle would trip dozens of times before the tank would fill. We ended-up driving a few extra miles and paying more per gallon at an older gas station that had an old gravity fed tank. I never did figure-out why Toyotas caused that problem with the sensor. Any ideas?

gaspain, a better solution for you might be to make something with a float and a limit switch. How large is the opening in the barrel?z

Posted: 5/19/2005 6:45:33 PM EDT

[#30]

Quoted:

gaspain, a better solution for you might be to make something with a float and a limit switch. How large is the opening in the barrel?z

a hole the radius of a can of soda and the filler nozzle takes up 3/4 of that. And the barrel needs to be filled within 1.0" - 0.5" of the top

Posted: 5/19/2005 7:09:20 PM EDT

[#31]

Quoted:
Cool replies! it looks like there is alot of ways to get'er done.

I asked the question because im trying to find a better way to fill wine barrels. I would like to leave them un-attended because it takes about 15 minutes to fill a 60 gallon barrel..and if you are filling alot of barrels thats a whole DAY of sitting next to a barrel trying to guess when its full so it doesnt overflow...and when it does overflow it shoots wine all over the damn place.

the way we do it now is stick a long stainless pipe into the top of barrel and use the speed control of the wine pump to to turn it on and off to filll the barrel. the pipe has to extend all the way down to the bottom of the barrel into the liquid so that it doesnt aerate the wine.

any ideas for an auto shut off?

If not a float switch, maybe a capacitive fluid detector hung around the bung of the barrel and protruding an inch or two into the barrel? This could be set to shut off a solenoid valve, or just shut off the pump motor, depending how precise you need to be. Piece of cake.

Posted: 5/19/2005 7:23:01 PM EDT

[#32]

a hole the radius of a can of soda and the filler nozzle takes up 3/4 of that.

Here's a cheap hack. Attach one wire to a small 12V power supply through a fuse and run it down one side of the nozzle. Attach another wire to the other side of the nozzle and run it to a normally closed relay that controls the power to the pump. When the wine hits the wires and starts conducting, the relay will trip and shut-off the pump. You then flip the power off to the pump before removing the nozzle. I did this for a system that filled-up 55 drums of soapy water. It worked very well as long as we made sure the drum wasn't grounded.

ETA:

filled within 1.0" - 0.5" of the top

The length of the wire can be adjusted control this.z

Posted: 5/19/2005 7:31:23 PM EDT

[#33]

a sensor at the end of the nozzle senses when it becomes summerged in gas instead of air and will shut it off

as the bubbling gas settles, continue to fill till the almount is rounded to the nearest dollar

Posted: 5/19/2005 7:32:52 PM EDT

[#34]

Quoted:
A mechanical switch inside the nozzle detects when the flow of air stops and shuts off the gas.

OK, can anyone explain why early to late 80's Toyotas don't work well with that sensor? When I started working at my current job, we had a couple of early 1983 Toyota Celicas, six 1985 Toyota pickups, six late 80's Camry's, and three late 80's 4Runners. I also personally owned a Tercel and a Corolla from the same time period. On all of them, the sensor on the nozzle would trip dozens of times before the tank would fill. We ended-up driving a few extra miles and paying more per gallon at an older gas station that had an old gravity fed tank. I never did figure-out why Toyotas caused that problem with the sensor. Any ideas?

The angles inside the fill pipe can cause gas to splash back into the nozzle. Holding the nozzle up or at a different angle than just sitting in the pipe normally. The sensor tube is usually at the bottom of the nozzle, but various cars' designs can make it register false positives. It really depends on the angle of the downward turn after the gas cap, and each model/year/make is different. Just don't pull the nozzle out too far or you'll end up negating the sensor alltogether and splashing gas all over the place, which isn't good for you, the car's paint, or the environment.

as for the wine filling thing... a float and a microswitch (and a relay to cut the pump power) makes the most sense to me, and it'd certanly be cheaper than the $80/nozzle that a gas pump runs.

Posted: 5/19/2005 7:39:54 PM EDT

[#35]

Quoted:
Quoted:
How does a gas pump know when your tank is full? ...then it shuts off preventing spillover?

You sure do come up with stupid shit!

Wow. Maybe you shouldn't waste your time here.

Posted: 5/19/2005 7:43:26 PM EDT

[#36]

in Oregon, it's done by the pump monkeys. But I guess that keeps unemployment down in that state.

Posted: 5/19/2005 7:46:42 PM EDT

[#37]

It's MAGIC!!

Posted: 5/19/2005 8:12:13 PM EDT

[#38]

As a technician in the petroleum field, one who repairs gas dispensors, and service stations in general
You guys are doing o.k. in your explanation of how nozzles work.

Posted: 5/19/2005 8:28:52 PM EDT

[#39]

www.straightdope.com/classics/a1_263.html

Posted: 5/19/2005 8:30:05 PM EDT

[#40]

It didnt work last week I looked back and saw about 4 gallons of $2.03 a gallon gas on the car and ground.

I had to use my people skills with the manager.

Posted: 5/19/2005 8:38:46 PM EDT

[#41]

I had to use my people skills with the manager.

Did you show him your war face?z

Posted: 5/19/2005 9:23:00 PM EDT

[#42]

Quoted:
When you fill your gas tank, some of the displaced air flows through the hole in the nozzle into the pipe. When the tank is full, the hole will be below the gasoline level and no air will pass through the pipe. A mechanical switch inside the nozzle detects when the flow of air stops and shuts off the gas.

You may have noticed that, after the pump shuts off, you can get more gas in your tank by pulling the nozzle out of the tank a bit. This is because you’re moving the position of the hole relative to the gas level and allowing the mechanical switch to reopen.

Correct. They had auto shutoffs LONG before the EPA was conserend about idiotic vapor recovery systems. Even back in the '70's

[ARCHIVED THREAD] - How does a gas pump know when your tank is full?

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