One finger over fuel pump nozzle hole prevents foam! Who knew?

[NarfBLAST]

I can not remember who mentioned this recently on these forums, I would like to thank them!

I tried covering the small 3/16ths inch hole on the underside near the tip of the fuel pump nozzle at my favorite Sunoco station and presto! The fuel came out clear without foam! Mind you it will only work at half speed without shutting off but that is perfect for venting! I topped up the tank in no time with no foam! And my finger did not get covered in diesel fuel, my hands were no more smelly than usual.

Why have I not heard of this before? Anyone else try this?

edit: added a video I made:

" title="YouTube video player"

edit: Here is a link to post #168 with thanks to @03TDICommuter for sharing this video:

edit: Here is a link to post #154 where the internal workings of the pump handle are explained:
http://forums.tdiclub.com/showpost.php?p=3307293&postcount=154

 

[Bob_Fout]

'Twas Whitedog.

 

[NarfBLAST]

Thanks Whitedog!

Bob, you ever try it?

 

[Bob_Fout]

I thought about it when I filled up a few days ago. I'll try it next time I fill.

 

[Powder Hound]

With my luck, I'll be swimming in diesel if I try this. I don't know how or why, but that's what'll happen.

 

[mrGutWrench]

With my luck, I'll be swimming in diesel if I try this. I don't know how or why, but that's what'll happen.

__. It's the port for the auto cutoff. I tried it. It just cut off the fuel flow, just like fuel had backed up in the filler neck.

 

[mrchaotica]

I found out the other day that B100 doesn't foam up either, even when it's pumped at full-speed.

 

[kcfoxie]

I found out the other day that B100 doesn't foam up either, even when it's pumped at full-speed.

Thats one of the reasons I loved B100. it was easier to hand calc your MPGs because it never foamed and thus you got accurate fills every time.

D2, not so much!

 

[Sip'n Diesel]

IIRC whitedog said he heard about it from... a female!

I still need to try this

 

[NarfBLAST]

__. It's the port for the auto cutoff. I tried it. It just cut off the fuel flow, just like fuel had backed up in the filler neck.

Yes it will cutoff if you request too much flow. I found that I could ease back to half flow and get a perfect stream with no foam, as soon as I let my finger off, it sucked in air and foamed, when I covered the hole again, it turned to clear within seconds... I repeated this three times to my amazement and before I was done having fun I could see clear fuel in the neck! I am not sure if it is important to rotate the nozzle 90 degrees or if some nozzles are different.

 

[Sip'n Diesel]

maybe someone could take a picture of the hole we're talking about... or is it blatantly obvious once you turn the nozzle sideways?

 

[mrGutWrench]

Yes it will cutoff if you request too much flow. I found that I could ease back to half flow (snip)

__. I tried it with the lowest perceptible flow possible. Still kicked off. In fact, I couldn't get it to flow at all - it just kept kicking off.

 

[40X40]

There are people with drivers' licenses that don't know how the automatic fuel shutoff works at the 'gas' station. Who Knew?

LOL

Bill

 

[weedeater]

Somebody named 'StinkFinger' came up with this?

 

[NarfBLAST]

There are people with drivers' licenses that don't know how the automatic fuel shutoff works at the 'gas' station. Who Knew?

LOL

Bill

I understand how it works, but I did not know that by covering the hole I could eliminate foam at flow rates as high as 50%. In all my experience trying to flow fuel at a "gas station" without foam I have never been able to get clear fuel to come out the end of the nozzle at more than maybe a 5% to 10% flow rate. I thought this would be of interested to people who fill their tanks until they can see "clear fuel without foam" at the top.

edit: okay, I have no idea how the automatic fuel shut off works other than it has something to do with the little hole.

 

[40X40]

I understand how it works, but I did not know that by covering the hole I could eliminate foam at flow rates as high as 50%. In all my experience trying to flow fuel at a "gas station" without foam I have never been able to get clear fuel to come out the end of the nozzle at more than maybe a 5% to 10% flow rate. I thought this would be of interested to people who fill their tanks until they can see "clear fuel without foam" at the top.

edit: okay, I have no idea how the automatic fuel shut off works other than it has something to do with the little hole.

It's difficult to put into words, but I will give it a try. The mechanism itself is simple, however.

When fuel flows at high speed through the nozzle it creates a vacuum or air flow INTO the 'little hole on the bottom' of the fill spout. This air flow is caused by a venturii effect and results in the air that goes into the 'little hole' going into the fuel stream inside the nozzle/handle... hence FOAM. It happens to gasoline too, but the bubbles burst immediately, ULSD foams less than the older LSD did.

When the fuel level in the tank rises it cuts off the airflow into that 'little hole' creating a temporary and sudden vacuum which acts on a diaphragm which in turn trips the cutoff.

If you use the auto-latch on a very, very low speed it might not shut off when the tank gets full..... the flow was too low to create enough vacuum to trigger the cutoff.

Did that make the operation clear? If not, ask...

I took lots of things apart that I found in the junkyard when I was a kid.

Growing up on the farm, we did not have an auto-shutoff on our pumps, but they had me (6 or 7 years old) and one of my earliest tasks was to sit on top of what ever was being filled and watch that it did no run over. We had a 100 gallon tank (gas) in the bed of out 1/2 ton PU and a pull behind two wheel trailer that held 250 gallons of D2. Both of these were filled with electric pumps at home and emptied (into tractors, etc.) by hand pump in the field. Any time a tractor came through the area where the electric pumps were at it was topped off since that was faster than hand pumping it later.. While the pump was running you hit the whole thing with a grease gun of course!

HTH

Bill

 

[NarfBLAST]

I am not sure it is as simple as no air in hole=pump shuts off. I think differential pressures between the hole and the nozzle come in to play or the mechanism doesn't work properly when the nozzle is rotated 90 degrees to reveal the hole...

Can't wait to experiment some more, and take a picture for poor Sip'n Diesel.

 

[40X40]

I am not sure it is as simple as no air in hole=pump shuts off. I think differential pressures between the hole and the nozzle come in to play or the mechanism doesn't work properly when the nozzle is rotated 90 degrees to reveal the hole...

Can't wait to experiment some more, and take a picture for poor Sip'n Diesel.

It's not 'no air in hole=pump shuts off"

It is SUDDEN stoppage of air flow pulls on diaphragm... Or a large enough vacuum from a big enough fuel flow.

Would you believe Cecil?

http://www.straightdope.com/columns/read/230/how-does-a-gas-pump-know-to-shut-itself-off

How does a gas pump know to shut itself off?
May 29, 1981
Dear Cecil:

Cecil, old buddy, even though I am receiving a doctorate this spring, the old adage that the more you learn the less you know still holds true. So tell me this: how does a gas station pump know when to turn off before spilling gallons of gas onto the pavement?

— Ethel Pumper, Dallas

Cecil replies:

Pal, you're going to need a doctorate to understand the following, so cleanse your mind of distracting thoughts. 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. Simple, huh? Sure, just like nuclear fission. Stick with English lit.

— Cecil Adams

How things work covered it too. They mention a vacuum pump but this vacuum is commonly generated by a venturi that needs no moving parts.

http://www.howeverythingworks.org/page1.php?QNum=1187
How does the automatic cutoff valve on a gasoline pump work? How is it able to shut off the gas before the nozzle has become immersed in the liquid? I don't see how the pump could be so sensitive to back pressure in the gasoline. — NG, Bloomsburg, PA


As you suspect, the pump isn't able to detect the change in gasoline pressure that occurs when the fill level reaches the nozzle. Instead, the nozzle uses several hidden components to shut itself off when the tank is full. There is a small hole near the end of the nozzle that becomes blocked by the liquid gasoline as soon as the fill level reaches that hole. Blocking this hole with gasoline is what shuts off the valve. There is actually a thin tube inside the main gasoline delivery hose that operates this valve system. That tube runs from the hole in the nozzle to a vacuum pump inside the gasoline-pumping unit. While the pump is dispensing gasoline into a partially filled tank, air flows easily into the nozzle's hole and the pressure inside the thin tube remains close to atmospheric pressure. But when the level of gasoline rises high enough, it essentially blocks the hole and the pressure inside the thin tube drops. This pressure drop is what triggers the valve and stops the gasoline flow. Look for the hole near the end of the metal nozzle next time you fill your car with gasoline. In most cases, it's easy to see.

HTH

Bill

 

[fitzski]

OK... filled up on the way home... it took 3min 15s to fill "normally" (i.e. no finger on the nozzle) for just shy of 58 litres and clear fuel right to the lip. That just doesn't seem like a whole lot of time to me to risk the stinky finger mod. How much time are you actually saving?

Had a look at the nozzle as well, and the hole is only about 1/2" from the tip on the underside. Seems kinda awkward to keep covered while filling. I wonder if the diameter of a wine bottle drip catcher would fit well (with a safety string attached!)?

 

[Sip'n Diesel]

OK... filled up on the way home... it took 3min 15s to fill "normally" (i.e. no finger on the nozzle) for just shy of 58 litres and clear fuel right to the lip. That just doesn't seem like a whole lot of time to me to risk the stinky finger mod. How much time are you actually saving?

well, I suppose that's where gloves enter the equation. also, note that sometimes you will get a lot more (or less) foaming sometimes depending on the circumstances

3min 15s sounds FAST to fill to the lip with no foam!

I haven't tried this yet, but for me this wouldn't be a time saver. I would only do it to avoid foaming. I don't like standing and waiting for the foam to go down to pump 0.10 gallons at a time. maybe it's just my imagination, but I seem to always get the really foamy stuff!

 

[Crazy Jetta TDi]

I did this the other day. I set the pump at full speed and then once it popped allowed it several seconds to let the foam settle. I then removed the nozzle and put my finger over the stink hole and preceded to full up at about 50% force. No foam was present out the nozzle tip and whoops out popped some D2 at me because I wasn't paying close enough attention to how fast it was filling up. Luckily none got on me. But, no foam and filled to the filler neck within seconds. In my opinion the small amount of D2 I got on my finger wasn't enough to shy me away from trying it again. Thanks for the tip.

 

[NB_TDi]

I just wait. Check the oil, fill the washer fluid.

Then finish off till I see the diesel. Guess I'm alone on that. Not sure why you'd want to smell like fuel.

 

[Got Bearings?]

I just wait. Check the oil, fill the washer fluid.

Then finish off till I see the diesel. Guess I'm alone on that. Not sure why you'd want to smell like fuel.

+1....

 

[Crazy Jetta TDi]

funny thing is, I didnt smell like fuel after filling up. It got such a small amount, no more than touching the pump handle with your bare hand, that to me it made the job faster and was worth it. But to each their own

 

[Thunderstruck]

Yuck, you touch pump handles with your bare hands? A toilet seat is cleaner than touching a pump handle. I always wear gloves. No glove, no ummm fill up love.

 

[Got Bearings?]

Yuck, you touch pump handles with your bare hands? A toilet seat is cleaner than touching a pump handle. I always wear gloves. No glove, no ummm fill up love.

I suppose you wear gloves each time you handle money.....

 

[Thunderstruck]

I do wash my hands after I handle it if I'm going to be touching food. If I get a sandwich and I'm not paying with my debit card, you're darned right I clean them.

 

[lekolite]

There's gotta be a tool in the making for this task. Toungue depressor with E-Tape on it? Toothpick held by pliers?

 

[truman]

There's gotta be a tool in the making for this task. Toungue depressor with E-Tape on it? Toothpick held by pliers?

How about a small diameter wide rubber band? When I tried putting my finger over the hole, the pump immediately shut down, at the lowest fill rate- first notch on the trigger handle.

 

[Thunderstruck]

Why not carry a little throw away piece of duct tape?