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  #1  
Old 10-27-2009, 09:19 AM
Heckity Heckity is offline
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Why do some gas pump nozzles click off?

My lack of scientific understanding is showing. Why is it when I'm self-pumping gas sometimes the nozzle clicks off . . . repeatedly. . . driving me crazy?

Is there some kind of vapor lock? Is there air in the line? Is there anything I can do to correct the problem whilst using the pump?

Thanks!
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  #2  
Old 10-27-2009, 09:27 AM
beowulff beowulff is online now
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The nozzles measure back pressure. Your gas tank is supposed to be vented, but if the vent is blocked, it might cause this problem (although it would probably set the Check Engine Light). I find that pulling the nozzle out of the filler neck a bit helps.
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  #3  
Old 10-27-2009, 09:43 AM
johnpost johnpost is online now
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don't click to the highest flow position and the pressure will be less. a slower rate should be OK. leave the nozzle fully in the filler tube, you don't want it to fall out or not trigger the shutoff well below the top of the tube.
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  #4  
Old 10-27-2009, 09:57 AM
JerseyFrank JerseyFrank is offline
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Move to NJ or Oregon where a pump jockey wouldn't deal with it for long before having it fixed. When I moved out of NJ I was amazed at the number of pumps that were bad. In my travels I thought it was my car or a random problem, but no... once you start going to the same self-serve station you remember that a particular pump is bad; and it never seems to get fixed.

I've had overflows, random shut-offs, broken pump clips, and the like when I pump my own. Now that I'm back in NJ, I never have these issues. All the pumps work amazingly well; but I can't say the same for the attendants.
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  #5  
Old 10-27-2009, 10:48 AM
KCB615 KCB615 is offline
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Quote:
Originally Posted by JerseyFrank View Post
I've had.... broken pump clips, and the like when I pump my own.
Per nearly every fire code in the country, you should never find a hold-open clip or other similar device on the dispenser nozzle at any self service filling station. The whole purpose of not having that clip (which in many cases is "broken" by the gas station management) is to require you to stand there holding the nozzle, so if something happens, you run, let go of the trigger, and the fuel flow stops.
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  #6  
Old 10-27-2009, 11:11 AM
MikeS MikeS is offline
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Quote:
Originally Posted by KCB615 View Post
Per nearly every fire code in the country, you should never find a hold-open clip or other similar device on the dispenser nozzle at any self service filling station. The whole purpose of not having that clip (which in many cases is "broken" by the gas station management) is to require you to stand there holding the nozzle, so if something happens, you run, let go of the trigger, and the fuel flow stops.
In my experience, it's not that universal. Nearly every gas station I've ever been to in the state of Indiana has the built-in hold-open clip; my recollection (from a road trip this summer) is that this is the case in Michigan & Illinois too. This may be because most of my refueling is done in towns and rural areas, rather than big cities — the fire codes in such areas probably aren't as stringent. Of course, the hold-open clip is designed so that the "kick" from the fill sensor disengages it automatically.

Last edited by MikeS; 10-27-2009 at 11:12 AM..
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  #7  
Old 10-27-2009, 11:46 AM
Xema Xema is offline
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Quote:
Originally Posted by KCB615 View Post
The whole purpose of not having that clip (which in many cases is "broken" by the gas station management) is to require you to stand there holding the nozzle, so if something happens, you run, let go of the trigger, and the fuel flow stops.
And yet essentially every pump used by a gas station employee has a hold-open clip, which is almost always employed - and which reliably shuts off the flow when the tank is nearly full, with no spillage. So somehow the gas pump knows when its being used by a common customer vs. a trained expert?
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  #8  
Old 10-27-2009, 12:51 PM
beowulff beowulff is online now
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Quote:
Originally Posted by KCB615 View Post
Per nearly every fire code in the country, you should never find a hold-open clip or other similar device on the dispenser nozzle at any self service filling station. The whole purpose of not having that clip (which in many cases is "broken" by the gas station management) is to require you to stand there holding the nozzle, so if something happens, you run, let go of the trigger, and the fuel flow stops.
Clearly wrong. At least in Phoenix.

I almost never visit a gas station without the hold-open latch.
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  #9  
Old 10-27-2009, 01:10 PM
3waygeek 3waygeek is offline
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Quote:
Originally Posted by KCB615 View Post
Per nearly every fire code in the country, you should never find a hold-open clip or other similar device on the dispenser nozzle at any self service filling station.
In my experience, the exact opposite is the case -- I can't remember the last time I found a pump without a working clip, even in California, whose consumer protection laws are generally very strong.
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  #10  
Old 10-27-2009, 01:15 PM
suranyi suranyi is online now
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Originally Posted by 3waygeek View Post
In my experience, the exact opposite is the case -- I can't remember the last time I found a pump without a working clip, even in California, whose consumer protection laws are generally very strong.
Agreed. In California, working clips are commonly found on self-service pumps.
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  #11  
Old 10-27-2009, 01:37 PM
Balthisar Balthisar is offline
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Even with the clip (or a wallet or gas cap jammed in), the pump will still turn off in the same circumstances as it turns off it you're standing there holding it.
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  #12  
Old 10-27-2009, 01:38 PM
pulykamell pulykamell is online now
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Quote:
Originally Posted by beowulff View Post
Clearly wrong. At least in Phoenix.

I almost never visit a gas station without the hold-open latch.
Same with the Chicago area. There are a number without the hold-open latch, but more than often I find them with the hold-open latch intact. I haven't paid enough attention to see if this is a suburbs vs. city thing, but not that I know of. The gas station nearest me requires me to stand there or jam my gas gap into the pump to hold open, but that's the only one I can think of off the top of my head that forces me to do that.

Last edited by pulykamell; 10-27-2009 at 01:39 PM..
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  #13  
Old 10-27-2009, 01:53 PM
BrotherCadfael BrotherCadfael is offline
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In our area most self-serve pumps have clips. There is one local convenience store chain which does not, and I avoid them for that reason. Unless they're the cheapest in town, which sometimes happens.
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  #14  
Old 10-27-2009, 02:37 PM
Irishman Irishman is offline
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At one time, I couldn't find gas stations with the clips intact. Now, they are back to being used. I have no idea what changed to make them disable them or what changed to make them start using them again. I just know I witnessed the difference.

The automatic shutoff when full kicks off even though the handle stays clipped. It's a separate mechanism.

For the OP, there is this
http://www.straightdope.com/columns/...hut-itself-off

Here's one with a (low quality) diagram.

http://www.answerbag.com/q_view/137434

And the best
http://science.howstuffworks.com/gas-pump5.htm

Quote:
Unfortunately, this shutdown can sometimes happen before the tank is full as the rapidly flowing gas backs up on its way into the tank. This can cause the gas handle to spring open before pumping is complete, leaving the annoyed customer to squeeze the handle again and risk the possibility of overflow. Pausing briefly will allow the gas to continue into the tank and the pump nozzle to start pouring gas again.
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  #15  
Old 10-27-2009, 10:21 PM
Askance Askance is offline
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Quote:
Originally Posted by beowulff View Post
The nozzles measure back pressure. Your gas tank is supposed to be vented, but if the vent is blocked, it might cause this problem (although it would probably set the Check Engine Light). I find that pulling the nozzle out of the filler neck a bit helps.
My experience is that it's the pump or the fuel, not the car. At my local petrol station I can literally never properly fill the tank, every pump either has a problem or is just set wrongly, or the fuel is excessively foamy perhaps. At it's worst you can squeeze and have it click off 20 times in a row with only a tiny amount of fuel getting through each time, drives us crazy and you usually give up with the tank only maybe 80% full. If I go to some random other station there's about a 50% chance I can properly fill up.
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  #16  
Old 10-27-2009, 10:33 PM
johnpost johnpost is online now
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Quote:
Originally Posted by Askance View Post
My experience is that it's the pump or the fuel, not the car. At my local petrol station I can literally never properly fill the tank, every pump either has a problem or is just set wrongly, or the fuel is excessively foamy perhaps. At it's worst you can squeeze and have it click off 20 times in a row with only a tiny amount of fuel getting through each time, drives us crazy and you usually give up with the tank only maybe 80% full. If I go to some random other station there's about a 50% chance I can properly fill up.
fill at a lower flow rate and the pressure will not build up and trigger the shut off.
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  #17  
Old 10-27-2009, 11:32 PM
Xema Xema is offline
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Quote:
Originally Posted by johnpost View Post
fill at a lower flow rate and the pressure will not build up and trigger the shut off.
Ah, but pumps increasingly exhibit a minimum flow rate that's actually rather high, which (probably by design) frustrates attempts to properly fill a tank. I have a van that routinely takes 5 gallons after the pump clicks off - and it can be a struggle to get that 5 gallons out of many pumps.
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  #18  
Old 10-27-2009, 11:55 PM
Darryl Lict Darryl Lict is online now
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Quote:
Originally Posted by Askance View Post
My experience is that it's the pump or the fuel, not the car. At my local petrol station I can literally never properly fill the tank, every pump either has a problem or is just set wrongly, or the fuel is excessively foamy perhaps. At it's worst you can squeeze and have it click off 20 times in a row with only a tiny amount of fuel getting through each time, drives us crazy and you usually give up with the tank only maybe 80% full. If I go to some random other station there's about a 50% chance I can properly fill up.
Exactly. The problem only occurs at shitty podunk stations. It rarely happens at any major brand gas station. I end up holding the lever in just barely and fill the tank at some ridiculously slow rate.
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