piclist 2008\07\11\103543a >
Thread: Fuel economy measurement across the globe
www.piclist.com/techref/index.htm?key=fuel+economy+measurement
face picon face BY : Sean Breheny email (remove spam text)



Hi Olin,

I may be relatively young (28) but I've been driving for 10 years and
certainly have filled up a car before :)

Let me try to rephrase my question by giving an example.

Let's say I go to fill up. First, I slide my credit card and select
the type of gas I want. Then I remove the nozzle and place it into the
filler tube in the car. Next I squeeze the handle and the pump starts
pumping fuel.

When the tank fills and the nozzle detects gas next to the small holes
on the outside of the nozzle, it closes the valve at the nozzle and
the gas stops flowing. I could "top it off" by continuing to cycle the
handle through open and closed.

Now, I put the nozzle back into the holder on the pump and complete
the transaction. At this point, the entire tube from the pump to the
nozzle is still full of gas, right?

Now if I remove the nozzle from the holder again, without swiping my
card again, and then squeeze the handle, how come I don't get the
contents of the tube spilling out? Sure, the pump will not deliver
more gas into the tube, but I would think that the gas inside the tube
could still come out.

I can only think of a few ways this could be prevented:

1) suck the fuel back out of the tube into the pump
2) somehow enable the pump to signal the valve at the nozzle to remain
closed when there isn't an active transaction going on.
3) Have the entire connection from pump through to nozzle be so air
tight that no air could get back in to displace the gasoline so that
it will not come out unless the pump is pumping (I'm having trouble
trying to determine whether this would work as it seems that normally
even a tube which is sealed at one end and filled with liquid can
still be emptied from the other end).
4) have the valve at the nozzle end require a minimum pressure to open
(which is greater than the pressure developed by gravity on the
vertical height of gasoline in the tube)

My question is which of these is done (or what possibility did I not consider)

Thanks,

Sean


On Fri, Jul 11, 2008 at 8:48 AM, Olin Lathrop <olin_piclistKILLspamspam.....embedinc.com> wrote:
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