Our chipmunk has always tended to draw slightly more fuel from one tank than the other. We have completed a five year re build (C of A May 2007), which included new 12 gallon tanks, removing and stripping both the sumps, the one way valves and the on off valve together with the associated plumbing, also the breather valves were removed cleaned and checked and the inverted flight breather pipes removed and refitted. However, the aircraft now draws about 2 gallons from the starboard tank before commencing to draw from the port tank. Thereafter it appears to draw frrom both tanks. The difference on refuelling is usually about 10 to 12 litres.
It does not matter whether circuits are left or right; the aircraft is in balance and in trim (flies straight and level hands off). We have checked all the breathers, swopped over the one way valves and the filler caps and checked for leaks. The differential consumption remains a constant whether on cross country or in the circuit. I have spoken to another chipmunk operator at my location who says he has the same problem and has had it since he took over the aircraft.
I think it must be an air pressure problem since the one way valves have no spring and rely purely on pressure differential. The on off valve is after the tank feeds join up and therefore cannot be a part of the problem. Any ideas please??
