Pump in Tank

The way pressure regulation is performed with fuel injection, and an
electric in tank pump prevents vapor lock. The pump pumps fuel up to the
fuel rail. The pressure is regulated by a valve which opens and returns fuel
to the tank over a second line when the desired pressure is achieved. That,
and the fact that you are dealing with a pressurized line from the tank to
the fuel rail, rather than a line where you are trying to "suck" the fuel
from the tank to the intake of the pump. So... BOTH conditions you
mentioned - pressure and flow - are always present with fuel injection. Any
fuel vapor in the line when the vehicle is turned off is instantly
compressed into tiny bubbles as soon as the pump pressurizes the line when
the key is turned on. Those tiny bubbles will be swept through the fuel
rail, and into the return line when the pump restarts when the vehicle
starts.

 

There was a spill two weeks ago at a station near my home. It was
caused by someone sticking the fuel cap in the handle as most
self-service stations in PA don't have ratchet piece in the handle to
allow the pump to be locked on. I remember wondering (as I read the
sign warning consumers of their liability for spills and warning them
not to leave the pump unattended while fueling) what the clean-up was
going to cost the guy as the station owner put containment "snakes"
around the spill and waited for the hazmat folks to arrive.

I wouldn't expect you to from what you've posted already. Some folks
don't have a lot of common sense. Fires from static caused by plastic
gas jugs and sliding across the seat in your car also rarely happen, but
they do happen and it takes little to prevent them. However, many folks
just think it won't happen to them.

Matt

 

You missed my point entirely. This has nothing to do with fuel
injection. A similar closed loop system could just as easily be used
with a carburetor.

Matt

 

I have to wonder about the details.l If the pump had a ratchet handle, it
may have actually prevented the accident. For the system to work properly,
the nozzle has to be inserted at least a little ways intot he filler neck.
How far, I don't know. If the cap sticker did not properly place the nozzle
because of the cap, it may have caused the problem. It may have fallen out
of the filler pipe completely. Could be a lot of stupid things. Some
people should not be allowed to pump gas under any circumstances.

See, that is where we differ. I have a lot of common sense. If I have to
get back in the car, I do ground myself long before reaching the filler
area. Common sense will prevent many accidents. Since many people have
none, it may be best to have full service again. Some towns in MA and the
entire state of NJ forbid SS for that reason.

 

This is not a problem of sticking the gas cap in the handle. The pump
nozzle is required to sense when fuel is up in the filler neck. That's a
defective pump nozzle, not a problem with ratchets or gas caps.

 

Boy! I'm glad I ask about why do they put the Fuel Pump in the Gas Tank!I
became very interested in the fact it turned into an open forum of about
gassing your car!Now I can talk from experience and it is the best
teacher! Do Not Put the nozzle on automatic and get back into the car!
Leaving it to wash the W/S is bad enought!I have owned Sevice stations and
Later I hauled Gasoline to Service Stations and to the Farmers! Gasoline
does not make friends!I have seen countless failures of automatic nozzles!
It scares me the most when someone smokes while pumping the gas! My son was
caught on fire with gasoline, It burns fast and terribly! Just don't take
the chance PLEASE!!!!Now back to the original thing on vapor lock! I am
very familiar with vapor lock! can be cured on the older cars very easily.
It always ocurred between the fuel pump and carbureator due to the motor
heat va[porizing the gas in the line!About 2-3 clothes pins would act as
heat sinks and stop the problem-

 

Mechanical pumps usually put out about 6-8 psi, whereas electric pumps are
typically regulated to 35 to 60 psi, while being capable of delivering up
to 90 to 100 psi. The fuel pressures necessary to operate the fuel
injectors led the way to the use of the electric fuel pump.

 

If the system is functioning as designed, it cannot vapor lock. The system
should keep 20 to 25 psi in the line forever (until the line is opened).
You have a regulator and a fuel pump check valve that should prevent the
fuel pressure from going below that level.

 

Mechanical pumps can easily be designed to put out a lot more than 6-8
psi. Think diesel injector pump. I don't think pressure had anything
to do with the move to electric fuel pumps. I don't know all the
reasons why the move was made, but I think it is simply better all
around to push the fuel rather than pull it and it would be very hard to
get a mechanically operated fuel pump back by the fuel tank!


Matt