Pump in Tank

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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.
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hyundaitech wrote:

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
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taters2 wrote:

Less chance of vapor lock is one reason.
Matt
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Matt Whiting wrote:

Fuel injection pretty much eliminated that problem, though your point is still valid.
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Brian Nystrom wrote:

I haven't seen a fuel injector yet that takes fuel direction from the tank and injects it into the engine. The fuel needs to get from the tank to the point of injection so there is still lots of fuel line that can vapor lock if not under pressure or with sufficent flow. Fuel injection doesn't change much with respect to vapor lock.
Matt
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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.
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Bob wrote:

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
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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.
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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-
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