On 04/26/2012 08:11 PM, Raimo Toivio wrote:
> I have two guestions:
> 1) would it be wise to have a 2nd fuel valve in a fuel return line also
> to get an ability to close it or one-way-valve in the case of emergency?
I have a one-way valve in the return line for exactly this reason.
> 2) why this line is connected to the fuel outlet which locates in the
> bottom of the tank? Why not to the upper corner of the (reserve side) tank?
This fuel might be quite warm. Imagine when your tank is half empty. The
hot fuel will have to make a free fall before it reaches the pool of
fuel, and it will probably evaporate before it even gets there. No big
deal as the tank will vent it away, but you might find that your fuel
consumption is a tad high. It is better that the return fuel immediately
enters the cold fuel in the tank, so even when some fuel has already
evaporated and produced bubbles, it will condensate back into useful
fuel when it contacts the cold fuel. So the bottom of the tank is the
correct position, and so it is depicted in the build manual anyway.
> So, I have noticed no problems to use my engine with return line which
> is off-line. There are also many Rotax aplications with no plans for
> return lines in use. What is a main reason we should have a fuel return
> line? To get more fresh cool fuel or what?
I can't say this for the 912, but for the 914 it is to avoid vapor lock,
so yes, to get cold fuel all the time and to avoid keeping it longer
than necessarily in the hot engine compartment.
Frans
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