Reason for electric fp at rear
- Thread starter Don
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JSeery
Member Emeritus
Similar to the reason most factory installed electric fuel pumps are instilled as close to the fuel source as possible. If fact inside the tank is best of all. Vapor pressure is related to the temperature/pressure at which a liquid transitions to a vapor. This is what leads to vaper lock. The further distance you pull a liquid or raise it in height the lower the pressure. Pushing a fluid slightly increases the pressure, pulling a liquid lowers the pressure. By locating the pump near the fuel source and as low as possible you get the best performance. It has little to do with it being an electric fuel pump, it is just an option to improve fuel delivery that would not be feasible with a mechanical pump.
34PKUP
Well-known member
Aren't all electric pumps mechanical?
V8COOPMAN
Well-known member
Seery.....That was a lucid, well-broken-down, yet to-the-point description of just about ALL of the factors involved with a reasonably simple fuel system, as well as the considerations necessary to move said fuel from tank to engine. DD
JSeery
Member Emeritus
Have no idea what that is referring to, but as a guess, a pump that is powered from an electric source vs a pump that is powered by some form of a mechanical arrangement such as a push rod or lever arm. It refers to the energy source, but still not sure what the point is? One would assume that it is understood what an electric fuel pump refers to, but apparently not!
JSeery
Member Emeritus
V8COOPMAN
Well-known member
Well maybe not, appears I failed to define what an electric fuel pump refers to!
Yeah, like I said, you're an idiot! DD
34PKUP
Well-known member
It was just a simple question, no point to be made. Sorry that you could not answer it.
JSeery
Member Emeritus
Well, I attempted an answer. Really don't understand the question. Maybe if you stated it a different way it would help. The pump that sets on the back of a flathead and operates off a pushrod on the cam is commonly referred to as a mechanical fuel pump. An electric fuel pump is wired into the electrical system and can be mounted anywhere. Some electrical pumps have a motor that turns a pump and some work on impulse like a solenoid. The term "electric" fuel pump refers to the fact the pump requires an electrical connection to power it and not how the pump works internally.
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Phil Gillespie
Well-known member
Normally the electric fuel pump if mounted near to fuel tank or underneath the car, because of this location will always have a positve head pressure on suction side of pump, hence pump will normally always push fuel through provided fuel in tank, or if filter is mounted before the pump this could be a problem.
The mechanical pump on the other hand does not have a constant positve head and relies upon tight leak free connections on suction side to begin to draw fuel from the tank.
As already mentioned the motive power defines electric or mechanical and not pump design, which may be centrifical or positve displacement in its pumping action.
Phil NZ
The mechanical pump on the other hand does not have a constant positve head and relies upon tight leak free connections on suction side to begin to draw fuel from the tank.
As already mentioned the motive power defines electric or mechanical and not pump design, which may be centrifical or positve displacement in its pumping action.
Phil NZ
skidmarks
Well-known member
Electric ad on pumps. I had a napa guy say one time you want that old style SW electric pump? Why not use the electronic pump...its better.
The old style i remembered was a lot heavier and had a diaphragm . The one he called electronic was half the size and weight.
Whats the difference inside?, they both worked on 12v
Briggs and onan and im sure others had a diaphragm pump that mounted to the flywheel shround and functioned off the magnet on the flywheel that also powered the magneto
The old style i remembered was a lot heavier and had a diaphragm . The one he called electronic was half the size and weight.
Whats the difference inside?, they both worked on 12v
Briggs and onan and im sure others had a diaphragm pump that mounted to the flywheel shround and functioned off the magnet on the flywheel that also powered the magneto
Some really good answers here that's for sure especially JSerrys efforts. Most electric pumps over the years on production cars were mounted in the rear close to the fuel tank. Some were mounted in the engine bay like the SUs on Morris Minors and Oxfords etc. At the rear and at the lowest level of the tank is the best position for them to be mounted. Here they are self primed because the fuel level in the tank is higher than the pump and they will push the fuel much better than they can pull it. Regards, Kevin.
The electric pump manufacturers recommend installing a filter between the tank and the pump. That means crawling under the car to change it with a rear mounted pump. No thanks. I've had enough fuel running down my arms. I just moved my pumps, two of them in tandem,(one is a backup) and the filter into the engine bay mounted on the frame rail. I can observe the filter and change it by the side of the road if it ever came to that.
50fordcoupeman
Well-known member
I installed a shut-off valve next to the tank for the same reason. No more fuel running down my arms!!
drolston
Well-known member
Easier and more reliable way to prevent fuel down your arm. Put a service loop of rubber fuel line on either side of the pump. Pinch both sides with vice grips or a clamp before you disconnect from the filter or pump. The service loop will also allow you to bypass the filter should you be stalled without a spare.
Blurry picture, but you get the idea. The pump is protected inside the frame rail and the inlet is slanted down, as recommended by the pump manufacturer.
Blurry picture, but you get the idea. The pump is protected inside the frame rail and the inlet is slanted down, as recommended by the pump manufacturer.
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Mart
Well-known member
I buck the system and have auxiliary pumps on my roadster and 33 coupe. They are both mounted up front and pull. They pull ok. They are only used for priming to aid starting after sitting, so intermittent use rather than continuous.
Actually the roadster has an advantage as it is a 30A and retains the cowl tank so probably not a great example, but it certainly works on my 33. They are SU type diaphragm pumps.
Mart.
Actually the roadster has an advantage as it is a 30A and retains the cowl tank so probably not a great example, but it certainly works on my 33. They are SU type diaphragm pumps.
Mart.