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Originally Posted by Kento
When the gas station tanks are full, the pressure at the nozzle is usually pretty high when you pull the pump handle all the way, and if the nozzle is at a hard angle in the fill tube, the splashing will often cause enough pressure to trigger the shut-off valve.
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I own a Chevron station in South Miami and the above statement is incorrect. The levels of the underground tanks have absolutley no correlation with the pressure at the dispenser hose. What causes the variation between a fast dispenser & a slow one is the actual fuel filter inside the dispensers. Cheapr station owners don't ever change the fuel filters, which causes a nasty buildup of residue in the filters, causing a slower flow of fuel to the hose & nozzle, just like an old fuel filter in your car would ceuse the same symptoms.
I actually test my dispensers on my jeep every month and using a stopwatch, if I can't pump 10 gallons under a minute, I change the filters....this tends to happen normally every 6 months. Regardless of which dispenser is slow, I change them all. Each grade in each dispenser has it's own filter (12 filters in my station). It's a pain in the ass to do, but well worth it when customers with SUV's comment on how nice it is to fill up & leave in under 5 minutes. I used to have a Tahoe and some stations it took me 20 minutes to fill up 30 gallons.
That said, when a dispenser is well maintained, the pressure from the nozzle can be extremley high, causing a little gasoline to splash up into the little holes around the tip of the nozzle. These holes are meant to vacuum the fumes being pushed out of the vehicle's tank and send them back in to the tanks underground to minimize air pollution. The hoses we use are two-way hoses. One line inside the hose delivers fuel to the car, the other sucks up fumes using an air/vapor pump. When liquid gas is splashed into these holes, the pump sucking the fumes out triggers and stops the flow of gas to the car.
Another problem that causes the dispenser to stop, is an old or damaged nozzle. These things are somewhat sensitive and if they are slightly bent (from being dropped or when some genius drives away with the hose in the tank and the line breaks away) the assembly in the nozzle might get a small drip of gasoline into the holes causing the same to happen. A similiar thing happens with some certain car models that either have kinked fill tubes, or poor designs from the factory. A lot of customers with the new Ford Mustangs & Escapes complain about the dispensors clicking off.
Sorry for the Gas Station 101 course...just thought someone might benefit from this basic knowledge of how a gas dispenser works (by the way, there are no gas pumps above ground...only underground. That's why up top they are now called dispensers, not pumps. When a customer pulls the lever to pump gas, it triggers the pump in the tank underground on and the gas flows under the pavement from the tanks up througt the dispensers & into your car.)
Enough.
-Ian
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