Dual tank fueling configuration

marc

Lifetime Supporter
So I finalized the fuel configuration for the RCRP4. This is a dual tank (one in each "sponson", and will be feeding a hungry LS7 with fuel injection. I have -10 AN fittings for the supply side at the bottom back of tanks, -6 AN fittings 5" above the supply for the return lines. I am connecting a 100 micron fuel filter (SS Mesh) before a Aeromotive A1000 pump then a 10 micron filter after the pump with a checkvalve. This will connect from each bank and meet between the rails at a regulator that will feed back to either tank via manual selector. Pumps will be run individually and electrically from the cockpit. I will see if I can setup a cable operated tank selector rather than run the fuel into the cockpit. I confirmed this setup with Aeromotive, and I just need to get the check valves as I bought the rest of this stuff (and it is $$$) already.
 
Marc, Been there, done that. The A1000 pumps don't like being starved for fuel, even for a few seconds. It is cumulative and even though you can starve the pump multiple times, it wears them out very quickly. I destroyed two of them.

The starvation in my case happened when the fuel level was low in the tank and under braking. Fuel would run away from the pickup. Problem solved by going to two low pressure Walbro lift pumps (one for each fuel tank) feeding a small tank which holds about a gallon. The A1000 feeds out of that tank. Overflow from the small tank goes back to whichever main tank is in service via a Pollak valve. I use two toggle switches to select which tank. An LED on the dash tells me that the Pollak valve has shifted properly. See the attached document for fuel and wiring connections.

The Walbro pumps I use are no longer made, but I think they have a new substitute pump. These lift pumps don't mind being starved for short amounts of time. I've had no further failures since going to this system.

Dave
 

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Ian Anderson

Lifetime Supporter
Dave

I too use a Pollack cross over valve - works great but I'm at 250 hp and run 8mm pipes throughout.

I'm not sure the Pollack would flow enough fuel for a thirsty LS7

Ian
 

Julian

Lifetime Supporter
The Pollack valve is normally used on the return side of the high pressure feed tank, so only has to flow the excess fuel back to the respective fuel tank.
 

Ian Anderson

Lifetime Supporter
Hi Julian

Not so

If you return from fuel rail to main tank and the LP pump is sucking air (Braking on low tanks or long downhill section)- the HP pump will drain the swirl pot very quickly.

The return from the fuel rail should return to the swirl so as not to get into this situation.

I look at it as 2 systems
1)
Tank - pollack to filter - LP pump to swirl (2nd from bottom outlet)
Return from swirl (Top most outlet) to tank


2)
Swirl ( Bottom outlet)- filter to HP Pump, to rail
Return to swirl (2nd from top outlet)
(Unless the LP pumps stop the HP pump should always have some fuel)

But I cannot see a really thirsty lump being able to be sufficiently fed through the 8mm Pollack fitting. - But I may be wrong.

IAn
 
Referring to the drawing I attached above, I run 10AN from the swirl pot, through a 100 micron filter, the pump, and a 10 micron filter. From the 10 micron, I use an 8AN that Y's into each fuel rail. From the opposite end of each fuel rail, I use 6AN to the pressure regulator, and 6AN from it back to the swirl pot. This is the high pressure loop that flows only from the swirl pot to the engine, and back to the swirl pot. Suction is from the bottom of the swirl pot.

The low pressure loop uses an 8AN line from each tank to the suction of a Walbro pump for each tank. There is 1 LP pump for each of the main tanks. They are connected with check valves so fuel cannot transfer from one tank to the other. Either of the LP pumps (but interlocked so only one LP pump can run at a time) fills the swirl pot with any excess from the swirl pot running through the Pollack valve back to the correct tank.

The Pollack valve has barbed fittings that fit well in 6AN rubber hose. I use Aeroquip SS braided rubber hose with screw type hose clamps on the Pollack valve. The Pollack valve is however made of a plastic/composite type material. I would never use one on a high pressure application.

6AN anywhere on the fuel supply side would be pretty small for a thirsty engine. In my case, the Pollack's job in life is to simply route excess fuel from the swirl pot back to the correct tank.
 

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Julian

Lifetime Supporter
Ian,

I think we are almost on the same page, agreed the HP regulator should feed back to the swirl pot.


I look at it as 2 systems
1)
Tank - pollack to filter - LP pump to swirl (2nd from bottom outlet)
Return from swirl (Top most outlet) to tank [\Quote]

This is where I got confused, as I would have the LP pumps (one per tank) to feed directly from their fuel tank (via filters) to the swirl pot and the pollack be on the outlet side of the swirl tank. The pollack then switches with the respective LP pump selected to direct fuel back to the tank it came from so you cannot cross fill independent fuel tanks.

Is your way utilizing a fuel tank balance crossover effectively providing one tank?
 

Ian Anderson

Lifetime Supporter
Ian,

I think we are almost on the same page, agreed the HP regulator should feed back to the swirl pot.


I look at it as 2 systems
1)
Tank - pollack to filter - LP pump to swirl (2nd from bottom outlet)
Return from swirl (Top most outlet) to tank [\Quote]

This is where I got confused, as I would have the LP pumps (one per tank) to feed directly from their fuel tank (via filters) to the swirl pot and the pollack be on the outlet side of the swirl tank. The pollack then switches with the respective LP pump selected to direct fuel back to the tank it came from so you cannot cross fill independent fuel tanks.

Is your way utilizing a fuel tank balance crossover effectively providing one tank?


Hey I'm a tight arse! (Must be something about my Scottish ancestry)

I actually ony have 1 Low pressure pump (Facit Red top)
I run
Tank - Pollack - filter - facit - swirl - pollack - tank (So I am "sucking" through the pollack.

I let the pollack switch from tank to tank and the Facit runs and draws from either.

Ian
 
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