Originally Posted by
joeflyer
I do mine like the second diagram above except that I install two vent lines in the center tank and plumb each saddle clunk directly to the center tank. This eliminates the tee and reduces system restriction. Also I plumb each saddle tank and up to the center tank vents with 1/8" Tygon. The center tank clunk to the UAT is then plumbed with 5/32" Tygon.
DO NOT USE SEPARATE VENTS FOR THE SADDLE TANKS. They need to be teed to a single atmospheric vent. A friend used two vents and after he filled up fuel started dribbling out one of the vents. As the plane sat while he was getting ready to fly most of the fuel syphoned out. He took off and about one minute into the flight he ran out of fuel and crashed.
Joe
For all the doubting Thomas's to Joe's statement above about fuel syphoning, let me run this across. My F-4 saddle tanks are plumbed with a vent for each tank and pickups from each tank T'd together going to a JMP accumulator then to the pump. All lines are 3/16 right up to the pump inlet. I use the JMP dual taxi tank ( fitting to each vent). On three separate occasions upon taxi out, when the taxi tank lines were removed one tank continually proceeded to dump fuel out of the vent in very heavy stream. On all three occasions ,this was caught before takeoff. If not there is no doubt that I would have been out of fuel within a couple of minutes. When I tried to defuel using the Jersey, the tank that was dumping fuel from the vent would try to collapse. Any other time when I defuel, everything is normal. Lewis Patton and Keith Yates have both witnessed this. Any ideas ?