by pschwenn » Thu Oct 14, 2021 12:56 pm
As with many/most fuel injected engines, Rotax 912i, 914 & 915T require a return circuit of excess gasoline - not delivered by the injectors. The excess fuel returns to the fuel tank. This circuit requires a backflow cutoff - a one way valve - to prevent fuel coming from the tank into the return circuit. Rotax recommends such a circuit but does not detail one or provide one.
When I look at schematics of examples of such circuits I can't fully understand them because it's not just a single path: source, fuel line, one-valve, fuel line, tank. There's more going on, some kind of parallelism in lines of the circuit.
Who knows of a explanatory example? And of a particular type/capacity/... of valve to use?
[Related: I'm going to route the return thru the overflow space (small metal box at the top of the firewall) that contains the tank neck and then directly thru that neck not too far below the gas cap, on the theory that feeding it back lower in the tank risks putting it below the surface of the fuel and thus providing a back pressure. On the other hand, routing as I am means that return fuel will be running down the non-liquid gas above the fuel. Since the tank has a breather this means that highly aromatic gasoline may be constantly mixing with some air and thus either degrade (e.g. lose oxygen or additives) or increase the fire risk at the breather.]
Thank you,
Peter Schwenn
6514 41st Ave
University Park MD 20782
240-602-6931
N16XN under construction
N32SX @ KCGS (912iS being installed)
http://www.schwenn.comEaa4 - KCGS College Park MD