Monday, June 1, 2009

Pump Reflux Disease

Shwonk. Click.
Shwonk. Click.
Shwonk. Click. Shwonk. Click. Click. Click.
The man on the other side of the gas pump continued rounding up to the nearest dollar. I could feel the reverberations in the hose on my side as I filled my own gas tank. Finally satisfied the older gentleman closed his gas cap, took his printed credit card receipt from pump, climbed into his truck and drove off. My disbelief increased.

He did not need exact change.
He paid with plastic.
He did not need a number easy to remember.
He got a receipt.

At $2.45 and 9/10ths for a gallon for gas I don't understand rounding up. In the days when the service man would still pump your gas for you I remember rounding up. We paid cash then. It was easier not to hand coins through the window. It made sense to round up -- then. But times have changed. Now you can play pump-price games like these: I just paid $18.63 for less than half a tank of gas. What happened in the year 1863? (The Battle of Gettysburg was that year in the American War Between the States.) Or I just filled up for $42.34. Which Star Trek Generation would that be? (I don't actually know the answer to that one, although I know people who could figure it out.) But I digress.

The biggest reason for my astonishment at the man's persistence in rounding up is a little something I once heard about pump reflux. A little bit of internet research seems to confirm it so I'm going to pass it along:

When the vehicle tank nears full the pump uses several hidden components to shut itself off. One of these is a small hole near the end of the nozzle. Air flows from the hole through a thin tube within the hose back into the pump. As long as it can get air every thing's going to flow just fine. Gas goes into your tank, air flows out back to the underground storage tank.

As your tank fills the level of gas rises until it reaches the nozzle. As soon as the tiny hole in the end of the nozzle is blocked by gasoline the pressure in the tube drops shutting off the pump. If you keep clicking the pump you feed gasoline -- not air -- into that tiny hole/tube system (in other words, back into the gas pump). It's called reflux, like heartburn.

Putting it in less technical terms: Each time that guy clicked to round up, he basically pumped some of that gas back into the stations storage tanks, not into his truck. And seriously, isn't the price of gas high enough already?

The next time you're out pumping gas and it shuts off, take your receipt, climb back into your car, look at that odd number and try to figure out if the Mayan calender has that many years in it. Save yourself the shwonking, the clicking, and the extra 27 cents. You didn't really want to spend that much at the pump anyway, did you?

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