Much as Scott said, while not located near a tank for "pushing" >it is located at the lowest point in the system prior to it's upward bend to >the engine....thus pushing. >Dana Overall +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
While not claiming my system is the way to go I'll tell you what works for me and is now flight proven with (only) two hours of flight. I have a 12 1/2 gal tank in each outer wing panel and no header tank. I have two Facet pumps that are plumbed in parallel. I have a fuel line from each tank to a shutoff valve located on the front face of the forward spar just below my knees. Between the shutoff valves is a tee that takes a single line to the two pumps (in parallel) and from there to the firewall gascolator and on to the carb. The fuel pressure gauge is in line just past the pumps. Between that fitting and the firewall is my fuel pressure regulator. This setup allows me to use either/both pumps to pump from either/both tanks and check either/both pumps with a single pressure gauge. My standard proceedure is to fly with both tanks turned on using a single pump except for takeoff and landing. Each pump has a separate switch and indicator light for "on". Because I would go into "glide" mode soon after having to turn off my electrical system I installed a backup power source for the pumps. A small motorcycle battery on the firewall feeds a separate buss and uses separate circuit brakers and switches to the pumps. The only thing in common is the pumps and the wires leading to the instrument panel. The circuits are isolated using diodes so I don't get feedback from the main to backup buss. If I have to shut down my electrical system in flight I simply turn off the fuel pump switch of the operating pump and flip a single switch to bring a pump back on line with the backup battery. A switch next to my volt meter on the panel allows me to monitor the condition of my backup battery, "up" for aux battery, "down" for main battery. Checking the condition of the backup battery and exercising the pumps on the backup system is one of the first items on my checklist before engine startup. One of the drawbacks of this system is that it requires a high number of flare fittings and thus a greater chance for leaks. I had several concerns about such a system while designing it. 1. Would the pumps be able to prime the line and draw fuel being being located that far from the tanks. I tested the pumps using water (heavier than gas) and was able to draw at a height of 30 inches. Early taxi test in the yard using a fuel can suspended from and below the wing attach fittings indicated that was not a problem. 2. Would the pumps, in parallel, simply form a loop in the system and pump fuel in a circle through the pumps without a check valve on each pump. I plumbed the pumps "head to head" and could not pump fuel "backward" through the pump. I eliminated the check valves. 3. Would the pickup in the wings "unport" in flight causing the pumps to suck air. I concluded that if both tanks were turned "on" that one tank or the other should always have fuel at the fuel pickup during any given flight mode. The unported pickup should have fuel flowing through the line from the pickup that has fuel, it being at that moment the higher of the two. My early flights had approx 5 gal in each tank and with approx two hours of flight time I have yet to see a problem. Even if both tanks unport at the same time, and I'm not sure how I'd get that to happen, I still have the fuel in the carb to keep the engine running for a short period. In several hours of running before attaching the wings, several hours of taxi test, and approx two hours of flight time, the engine has not so much as "burped" once. As always, your results may vary. Whatever system you use you must do a fuel flow test to insure you have sufficent flow in all flight attitudes. Do these test on the ground, not in the air! There is no "one perfect setup". Just make sure you consider all the possible failure modes for whatever system you have installed. Larry Flesner Carterville, Illinois www.krgathering.org
