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Transfer Pumps and Fuel System Configuration

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wsimpso1

Super Moderator
Staff member
Joined
Oct 18, 2003
Messages
11,353
Location
Saline Michigan
I have a couple questions for folks.

My fuel system has a header tank on centerline to feed the engine and along slender wet wing tank on each side to supply to the header. I am planning on using a paired selector valve to both pick the tank to draw from and to send excess fuel back. The idea is that a full header tank just overflows back to the tank fuel is coming from. I do plan to put the fuel into the header tank up high to prevent siphoning when pumps are off. Since it is a low wing airplane, I will have to pump to the header tank. I was figuring on a couple low pressure continuous duty electric pumps, but then the exact configuration and which pumps become the question.

Configuration - So, am I better served to put the transfer pumps in parallel or in series between the selector and the header tanks? Why would I prefer series or parallel? I imagine if the transfer pumps are in parallel, each will need either an internal or external check valve to prevent the system with only one pump turned on from driving fuel around in a circle instead of keeping the header tank full. And if the pumps are better in series, will I need any check valves at all?

Pumps - Facet makes their Solid State, Dura-Lift, Gold-Flo, and Posi-Flo pumps. I have replaced a couple of the Gold-Flo over the years in the Archer, which is not confidence inspiring. Are any of these particularly bad or good? Then there are various models for bus voltage, fuel connections, flow and head, and check valves or not. Which ones should I use and WHY? Then there are many variety of race car pumps too. Any of those to particularly stay away from or gravitate towards?

Then we move to the high pressure pump that takes header tank fuel and sends it to the fuel injectors. Ross over at Simple Digital Systems sells a pair of Walbro pumps in a yoke that he really likes. Does anyone have reason to disagree? Ross just sent me a note explaining that each Walbro has a check valve and they normally run them one at a time, so that is cleared up.

Onto the bigger system - Where should I place the filters and gascolator? Default is like the Cherokee that has been so good to me - after the selector. This means I only need one filter and gascolator, but it also means that the selector and pump can see debris that the filter/gascolator might have caught. To put the filter and/or gascolator upstream of the transfer pumps means that I will have to pull fuel through the finger screen, four feet of 3/8” fuel line, through a filter and/or gascolator, then through the selector valve before finally getting to the suction side of the fuel pump. I suspect that this may be an unwise idea – can anyone conclusively say yes or no on that topic​? If Yes, I am putting the components lower than the tank, but how much can the pump do?

For discussion, there are systems out there where they put a pump at the wing tanks, pushing fuel through the filters and gascolator, then the selector. I am reluctant to do this way for a couple reasons. The first reason is that I not only will have to select the tank electrically (turning on its pump), but I also have to work a way for overflow fuel to return to the selected tank. Pump plus selector valve means an opportunity to screw up, using solenoid valves and such give more opportunities for fuel starvation. Next reason is that if I have a pump failure, all of the fuel on that side of the airplane is inaccessible. Last is that I then have to find places for twice as many gascolators and filters. I suppose I could install a panic switch that turns on both wing pumps and a standby pump too, but then I would have to add the system I am currently planning on in the first place on top of the other system components... see my problem?

Last thoughts – there is a rather long thread on herehttps://www.homebuiltairplanes.com/forums/showthread.php?t=30050&page=9, post 128 where a manufacturer uses jet pumps to move fuel from one place to another. Anyone know where to get these jet pumps and how much flow they need to work? That would remove the need for transfer pumps by simply using the excess flow from the high pressure pump to move fuel from selected wing tank to the header tank.

Billski
 
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