"One-way" fuel line valve..?

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French demon

French demon

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Hi all
My 198 slant starts very easily and fast when hot, but when it has been shut off for a couple of days, I have to crank several times to get it back to life. The time required for the mechanical pump to refill the fuel line and the carb bowl.

I planned to install an electric fuel pump, but I would like to try an alternative and easier solution : a "one-way" valve (or "non-return" valve) on the fuel line. It's cheap and very easy to install.
But is it efficient? Will it prevent the fuel line from emptying (or will the gasoline evaporate anyway?)..? And where's the best location to install it on? Just before the fuel filter?

A typical "one-way" valve :
valve anti-retour.jpg

François
 
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French demon said:
(or will the gasoline evaporate anyway?)..
Click to expand...
Yes, After a few days it will. I install electric fuel pumps along with the mechanical as a primer/booster using a manual switch.I don't drive my old car and truck daily. Before starting,hit the switch and allow the electric pump to prime and after it starts, several seconds later,turn the switch off. The mechanical pump will draw fuel thru the electric pump with the electric pump not running. Done this for years on many cars.Just my 2 cents.
P.S. Sounds like a very cool Demon you have !
 
Interesting primer-booster solution.
But is there any risk that the not-running electric pump does block the gazoline coming from the mechanical pump?

Maybe a parallel installation of both pumps (using "Y" connectors) would be better than a serial installation?

Something like that :
Fuel booster.jpg

What do you think about?
 
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French demon said:
Hi all
My 198 slant starts very easily and fast when hot, but when it has been shut off for a couple of days, I have to crank several times to get it back to life. The time required for the mechanical pump to refill the fuel line and the carb bowl.

I planned to install an electric fuel pump, but I would like to try an alternative and easier solution : a "one-way" valve (or "non-return" valve) on the fuel line. It's cheap and very easy to install.
But is it efficient? Will it prevent the fuel line from emptying (or will the gasoline evaporate anyway?)..? And where's the best location to install it on? Just before the fuel filter?

A typical "one-way" valve :
View attachment 1716161250

François
Click to expand...
It's probably just evaporation. Trying a check valve wouldn't hurt. We have had many discussions here about the subject and the only fix people rave about is the electric charge pump. Those that have tried the check valve don't say much about it after it's installed. Here's a link to the pump thread. Hook it up near the tank with fused power and a momentary pushbutton. Electric primer pump for fuel
 
French demon said:
Interesting primer-booster solution.
But is there any risk that the not-running electric pump does block the gazoline coming from the mechanical pump?

Maybe a parallel installation of both pumps (using "Y" connectors) would be better than a serial installation?

Something like that :
View attachment 1716161295

What do you think about?
Click to expand...
Just use a rotary vane pump that the fuel can flow through.
 
Mike and Darter, thanks for the tip
As the check valve is already ordered, I will try it and if it's not efficient, I will install an electric pump as a cold start booster...

I have a '68 Valiant instrument cluster installed into my Demon, and it has a very nice on/off switch ready for use (initially the flasher switch). Would be perfect for a momentary fuel pump boost. :)

68 Valiant cluster.jpg
 
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French demon said:
not-running electric pump does block the gazoline coming from the mechanical pump?
Click to expand...
No, and a 198 Slant just sips fuel. I even run that set up on a 472 Dual Quad Hemi. But I will say with all 8 barrels open it needs the electric pump on feeding the mechanical pump.
 
French demon said:
Interesting primer-booster solution.
But is there any risk that the not-running electric pump does block the gazoline coming from the mechanical pump?

Maybe a parallel installation of both pumps (using "Y" connectors) would be better than a serial installation?

Something like that :
View attachment 1716161295

What do you think about?
Click to expand...
Many years ago I started to put together a fuel system similar to this. My plan was to run a second 3/8” fuel line that started inside the tank. My plan was to run a fuel pressure sensor in the original fuel line. Once the pressure dropped to a certain point the electric fuel pump would energize. The fuel line with the electric fuel pump also had a check valve in it. My reasoning for dual fuel lines was that if the pumps were in series and the vanes in the electric pump could block or part block off the flow of fuel. The other thing is that the check valve would stop any fuel from the mechanical fuel pump to back feed through the electric fuel pump while the electric was not running. I never followed through with it though and I may have over complicated it.
 
Darter6 said:
No, and a 198 Slant just sips fuel. I even run that set up on a 472 Dual Quad Hemi. But I will say with all 8 barrels open it needs the electric pump on feeding the mechanical pump.
Click to expand...

As the slant-six fuel only sips fuel, is it possible to install the electric pump just ahead of the mechanical pump, on the rubber inlet hose? It's a lot easier than near the gas tank, especially for the power wiring.
 
French demon said:
As the slant-six fuel only sips fuel, is it possible to install the electric pump just ahead of the mechanical pump, on the rubber inlet hose? It's a lot easier than near the gas tank, especially for the power wiring.
Click to expand...
Those electric pumps are made to push the fuel. They have pressure not suction. You want them near the tank.
 
My pump :
EP-500.jpg
Isn't it able to aspire gas from the tank? It's given for 3-5 psi and 30 gallons per hour.
And if the mechanical pump is just behind it, the combined suction of both pumps won't be enough to quickly fill the fuel line toward the carb?
 
Any pump should push through the following pump, or pull through the upstream pump. I ran a REAR mounted NON energized pump on the street for years. ALL pumps have check valves. Whether or not they properly "check" is due to design, quality, dirt and debris, and wear

TWO things (or more) have changed since the old days. Quality of components, and the chemistry of the fuel. Alky gas evaporates, vapor locks, and boils more easily than the fuel we knew as kids
 
French demon said:
My pump :
View attachment 1716161399
Isn't it able to aspire gas from the tank? It's given for 3-5 psi and 30 gallons per hour.
And if the mechanical pump is just behind it, the combined suction of both pumps won't be enough to quickly fill the fuel line toward the carb?
Click to expand...
In theory, that should work. I would mount the pump near the tank simply because that's the way it's designed to work.
 
toolmanmike said:
Those work great if you are having vapor lock issues while the engine is running.
Click to expand...
Also helps with fuel evaporation and pressure on the seat after shutting the car off when hot. Start the car up when cold and shut it right off, Then let it sit you'll see the difference. I didn't believe it either until it was shown to me.
 
After all these good advices, in order, I am going to try the installation of a check valve. Then, if not efficient, I'll try the electric pump into the engine bay. And then, if it still doesn't work, I will mount the pump under the gas tank.

:thankyou: for all, Sirs

François
 
Once the motor cranks 2 revolutions, stop cranking.
The mechanical pump has been cycled, the spring and diaphragm inside the mechanical pump is still sucking fuel by way of the diaphragm and spring, adding an electric pump to pump fuel already being sucked is not nec.
By waiting a few seconds not cranking, the fuel keeps moving by the vacuum/spring pressure, - then crank another 2 revolutions, that recycles the mechanical pump to re-supply the suction vacuum.
Crank- crank- crank- cranking is like continuing to pull the trigger on an emptied chamber, - wait .


Study how a mechanical fuel pump works, it already has 2 one-way/check valves built into it !

Once the spring is pulled, that cycles the diaphragm .

Have you Ever pulled a fuel line off, a long time after the engine was running, and get a shot of pressurized fuel, - that same spring holding pressure is the same spring pulling/holding vacuum to the fuel tank, - even when the engine is NOT turning ! !

IMG_20231102_155107.jpg
 
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The fuel pump itself—the original mechanical one—already contains the valve you have in mind, in the form of the fuel pump's output check valve. Sometimes they grow leaky with age (and these days, with the poor quality of available fuel pump, sometimes they're leaky from new).

An electric fuel pump requires thoughtful installation, or it's unsafe; see here.
 
c
French demon said:
Hi all
My 198 slant starts very easily and fast when hot, but when it has been shut off for a couple of days, I have to crank several times to get it back to life. The time required for the mechanical pump to refill the fuel line and the carb bowl.

I planned to install an electric fuel pump, but I would like to try an alternative and easier solution : a "one-way" valve (or "non-return" valve) on the fuel line. It's cheap and very easy to install.
But is it efficient? Will it prevent the fuel line from emptying (or will the gasoline evaporate anyway?)..? And where's the best location to install it on? Just before the fuel filter?

A typical "one-way" valve :
View attachment 1716161250

François
Click to expand...
called a check valve ........
 
Ok, I tried a check valve, and the result isn't very probant.
I installed a pressure gauge onto the fuel line (just between the rigid line and the fuel filter) and the pressure with the engine running is good : 5 psi.
pressure.jpg
But when I shut the engine, the pressure goes down from 5 to 0 in a one minute delay.
If the fuel pump has integrated check valves, is this pressure drop normal?


Another question : my fuel pump has a vacuum port, directly connected to the carb. Is it an ECS requirement (my Demon is an ECS equiped car)..? What's the purpose of this vacuum port?
fuel pump ECS.jpg

:thankyou:
 
I would say losing that pressure in about a minute could be considered normal. Some pumps leak, some have actually tiny bypasses in the valves. Otherwise the line , hot, between the pump and the carb will heat and raise pressure, and force fuel past the needle and seat
 
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