Reason for electric fp at rear

[Karl Wescott]

Originally Posted by 34PKUP

Aren't all electric pumps mechanical?

No. There is such a thing as a magnetohydrodynamic pump. But that requires an electrically conductive fluid, which gasoline should not be. https://en.wikipedia.org/wiki/Magnetohydrodynamic_drive.

[Jack E/NJ]

>>>rubber fuel line on either side of the pump>>>

Rubber fuel tubing should be avoided on pump's pressure side if possible. On single line supply, safest is shortest pressure-side line as possible using all-metal flared tubing/fittings. Jack E/NJ

[FL&WVMIKE]

If a person does not want to rely on an electric pump, but wants to have one in case their mechanical one goes out, or use it to prime the carb, supplement the old mechanical unit, etc... a check valve can be used!

A check valve only allows the fuel to travel in one direction. In the picture, it is situated to only allow the fuel to travel towards the engine. Therefore, when the electric pump is turned on, it doesn't just push the fuel back to the tank. When the electric pump is turned off, the mechanical pump can draw the fuel around the electric one. The bold areas where the lines split are simple tees. Clever, eh?

Oh, Google 'check valve gasoline' and you will find plenty. They're also cheap.



Good Luck!

[JM 35 Sedan]

Originally Posted by JSeery

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.

JSeery, If you look at the history of this members previous postings, I think you will see a similar pattern on most every post. No problem with your post.

[FL&WVMIKE]

Originally Posted by JSeery

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.

This totally nailed the reason a pump works best at the tank. Fuel vaporizes/evaporates, and turns into a vapor. Putting it under pressure helps keep this from occurring. Putting it under suction actually helps it vaporize.

Engine driven (suction) pumps can only draw liquid fuel. If there is a big pocked of vapor in the line, they stop functioning, and are 'vapor locked'.

Engine driven (mechanical) pumps need to be at the 'engine'. Electric pumps are free to be placed anywhere, and the most effective/efficient place to put them is near the tank.

[JM 35 Sedan]

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@Mike Jr, I miss your Dad and his posts here. Met him about 7/8 years ago at one of Vic Piano's Florida gatherings. I used to kid him about selling me his 35.

[Tom Walker]

Originally Posted by FL&WVMIKE

If a person does not want to rely on an electric pump, but wants to have one in case their mechanical one goes out, or use it to prime the carb, supplement the old mechanical unit, etc... a check valve can be used!

A check valve only allows the fuel to travel in one direction. In the picture, it is situated to only allow the fuel to travel towards the engine. Therefore, when the electric pump is turned on, it doesn't just push the fuel back to the tank. When the electric pump is turned off, the mechanical pump can draw the fuel around the electric one. The bold areas where the lines split are simple tees. Clever, eh?

Oh, Google 'check valve gasoline' and you will find plenty. They're also cheap.



Good Luck!

Mike,
would it work if you just put a check valve between the original Ford pump and the carb?

Then the fuel never drains back, and there would not be a problem with the old mech pump running dry? Seems alot simpler than all these elecric pump solutions, or what am I missing?

Cheers, Tom.

[FL&WVMIKE]

Originally Posted by Tom Walker

Mike,
would it work if you just put a check valve between the original Ford pump and the carb?

Then the fuel never drains back, and there would not be a problem with the old mech pump running dry? Seems alot simpler than all these elecric pump solutions, or what am I missing?

Cheers, Tom.

A person could try that! It is a pain when the fuel drains out of the lines and back to the tank after sitting for a long time. I usually get out the starting fluid or pour some gas down the carb to avoid all the cranking.

With a Holley, you can pour some gas down the bowl vents to fill up the bowls. Might be able to do that on a flathead as well. Never tried.

My diagram was if a person wanted to mount an electric pump at the rear, but didn't want to rely on running it all the time. The check valve just kept it from pumping the fuel right back to the tank... so it turns into an 'optional' electric pump, that can also be used to prime the carb, or come into use when a mechanical pump goes out, driving down the road.

When we would take these old cars on long trips in the 1970's when I was a kid, we traveled from WV to Hershey, Charlotte, and all over the places. My parents even took the '35 to Vermont when I was a baby. Dad packed tools and spare parts for any long trip, and more often than not, we would end up having to fix something. lol On the V8's it was usually fuel pumps... sometimes the generator. For the Model A, it was usually a leaky water pump. The 'box' in the floor of the back seat of the '34 contained basic tools, an extra fuel pump, generator, distributor and water pump. At least, that's what I can remember.

The auxiliary electric fuel pump would have saved some time beside the road, changing out fuel pumps. lol