Fuel return port in gas tank lower than maximum fill level?
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Ian Anderson
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Alex
Something I was told years ago that still makes sense
Put a fuel pickup into the tank from a high point - that way if your fuel hose becomes disconnected you do not empty your tank on the floor (You may, on some systems get a "syphon" effect but that is rare
I know - I clumbed under my Formula V - cut off the connecting hose for the fuel filter and then remembered I had not drained the tank - I lay under the car for half an hour with my finger over the tank outlet till my brother came out to see what I was doing!
Ian
Something I was told years ago that still makes sense
Put a fuel pickup into the tank from a high point - that way if your fuel hose becomes disconnected you do not empty your tank on the floor (You may, on some systems get a "syphon" effect but that is rare
I know - I clumbed under my Formula V - cut off the connecting hose for the fuel filter and then remembered I had not drained the tank - I lay under the car for half an hour with my finger over the tank outlet till my brother came out to see what I was doing!
Ian
Ron Earp
Admin
Ding ding ding!
My Jensen Healey (RIP that POS) race wagon had a "cell" in the trunk with a low pickup point. When the driveshaft cut the tunnel in half and most of the cockpit it also cut the fuel line in half too. I still remember the dead quiet once the car came to rest track left and hearing the sound of fuel pouring out while the vapor wafted up around the cockpit.
I pull from the top and return to the top. Z and Lola both have this setup, with fuel safe plates, check vents, and rollover valves. Neither car has exhibited fuel related issues.
Alex,
I think you need to step back and take a look at what you want and consider fluid dnamics a little. If you have a carb setup, the return can be a little below the fuel level without any harm. A little back pressure is not going to affect the regulator with the flow you will have cosidering the fuel pump. If it does your only talking 1 maybe 2psi max. If you are using EFI, you have a 40# regulator and you would have to have the return lower than the height of your tank to be an issue.
Considering the vent. You will have a sealed fuel filler cap and you have to have a vent somewhere. It needs to be somewhere above the fuel level when full. otherwise when the fuel is heated, say after a casul drive somewhere, and the heat of the engine affects the air above the fuel level, the air has to have somewhere to go. Thus the vent. So if it is below the fuel level at any time(think parking on a slight incline) it will be forced out onto the roadway which is not a good thing. So I would think it needs to be above the highest level the fuel would ever be. That or you need two vents, one on each side of the tank, or front and back. This will keep the fuel in the tank where it belongs.
I also think you need to give the discriminator valve another thought. Its purpose is to let air in and out of the tank as the level changes. The valve will close when the fuel rises up in the line from a surge or from a bad parking angle. Under that senario though, the tank would become pressurized, requiring a second line. If you dead set on not using a discriminator valve, then you should think of a system like an overflow tank for the radiator, where there is a way to suck the fuel back into the tank keeping it off the street!!
Bill
I think you need to step back and take a look at what you want and consider fluid dnamics a little. If you have a carb setup, the return can be a little below the fuel level without any harm. A little back pressure is not going to affect the regulator with the flow you will have cosidering the fuel pump. If it does your only talking 1 maybe 2psi max. If you are using EFI, you have a 40# regulator and you would have to have the return lower than the height of your tank to be an issue.
Considering the vent. You will have a sealed fuel filler cap and you have to have a vent somewhere. It needs to be somewhere above the fuel level when full. otherwise when the fuel is heated, say after a casul drive somewhere, and the heat of the engine affects the air above the fuel level, the air has to have somewhere to go. Thus the vent. So if it is below the fuel level at any time(think parking on a slight incline) it will be forced out onto the roadway which is not a good thing. So I would think it needs to be above the highest level the fuel would ever be. That or you need two vents, one on each side of the tank, or front and back. This will keep the fuel in the tank where it belongs.
I also think you need to give the discriminator valve another thought. Its purpose is to let air in and out of the tank as the level changes. The valve will close when the fuel rises up in the line from a surge or from a bad parking angle. Under that senario though, the tank would become pressurized, requiring a second line. If you dead set on not using a discriminator valve, then you should think of a system like an overflow tank for the radiator, where there is a way to suck the fuel back into the tank keeping it off the street!!
Bill
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