Kitplanes FI Article

[PilotRPI]

In the latest kitplanes, there was a description of constant flow vs. pulse width mod. FI.

For the constant flow FI, it did not show a return line. Is this correct? In reading through the FI posts here, it seems that most FI systems have return lines, yet one post about bendix FI said it didn't have a return.

For the lower pressure pumps used for carbs in something like an RV7 or Cherokee, do they have any type of return lines?

If anyone has some links for fuel flow diagrams for different systems, it would be much appreciated.

Thanks!

[DanH]

Jesse,

The descriptions in the article sidebar cover the two most common arrangements, but there are variations.

As noted, Bendix-style systems have no return line . Airflow Performance systems are often installed with a purge line, which is not quite the same thing as a return line. Continental FI systems have a vapor return line, but Continentals are not often found in RVs.

Classic electronic fuel injection systems (including the SDS-based system sold by Protek) return excess fuel to the tank after flowing through a pressure regulator. Recent automotive systems control fuel rail pressure with a variable supply pump, and have no return.

No return lines on carbed systems.

[N941WR]

Originally Posted by DanH

... Airflow Performance systems are often installed with a purge line, which is not quite the same thing as a return line. ...

To clarify, the purge line is not required and many have been installed without it.

A number of builders who do elect to install the purge line, will "T" it in before or after the fuel valve, not necessarily at the tank.