Electric pump failure on fuel injected engine

[Boomer506]

So I am getting ready to make my engine choice on my RV8 project, and I've decided that fuel injection is the way to go. The RV6 I built had a regular carb and fixed pitch prop. But I'm going with IO and CS on this one. I have some time behind fuel injected engines but I guess I don't fully understand them particularly wrt electric pump failure.

I'm getting ready to plunk down $600 for the Van's ES Airflow pump and filter, but what happens if that pump stops when I'm flying? Is there an engine driven pump that will keep me in the air? At all altitudes? Can I get a restart on the engine driven pump at lower altitudes or am I just going to have to find a place to set it down

[David-aviator]

The engine driven pump will save your bacon 24/7, have no fear.

Some 6 cylinder engines which produce more heat than 4 cylinders, may required the electric pump until climbing into cooler air. It is an issue of vapor lock before the engine driven pump.

[Boomer506]

Thanks David, I'm glad you have confidence in the system. The RV-8 plans ES Airflow pump show a recirc line from just forward of the pump but still aft of the firewall, back to the fuel selector. But I would think the recirc return line should be from inside the cowling where the heat is. It doesn't seem to make sense to recirc from an area that is already cool. You also see installations where the recirc line goes back to one of the tanks. I wonder if that makes a big difference?

[Toobuilder]

Just as a point of reference, I rarely use the boost pump in the Rocket. Cold starts to prime, momentarily when switching tanks, and right after a hot start is about it anymore. For the most part, the electic pump is a backup to the engine driven pump - it's normally not used in cruise flight.

[SHIPCHIEF]

I went the other route, I have 2 electric fuel pumps and no engine driven pump.
I keep a sharp eye on the voltage while in flight. Alternator failure would limit remaining flight to the questionable capacity of the battery.
There is an advantage though. Starting is always easy, because shutting down is done by running the RPM up to about 1500 then turning of the fuel pump. The fuel servo and spider are empty when the engine dies, so there is no fuel leakage into the intake manifold which causes a rich condition and difficult hot starts.
I have an Airflow Performance FM-150 system, and use 2 automotive fuel pumps and a turn down pressure regulator which routes unused fuel to the fuel return selector valve, then to a tank. It's a residual from my Mazda Turbo Rotary engine, but it works so well I kept it.

[xblueh2o]

Yep, The engine driven mechanical pump will work just fine. Consider the electric one as a back-up in case the mechanical one fails.

As for the pump itself, you could get the one from EFII that does not require a return line.

[DanH]

Originally Posted by Boomer506

Thanks David, I'm glad you have confidence in the system. The RV-8 plans ES Airflow pump show a recirc line from just forward of the pump but still aft of the firewall, back to the fuel selector. But I would think the recirc return line should be from inside the cowling where the heat is. It doesn't seem to make sense to recirc from an area that is already cool. You also see installations where the recirc line goes back to one of the tanks. I wonder if that makes a big difference?

That's an old diagram. No current boost pump (Airflow Performance, Andair, or EFii) requires an external re-circulation line. Flow for pressure regulation is internal.

The line back to the tanks, as used with a purge valve or a Continental-style fuel injection, is an entirely different issue.

Last, do not redesign the fuel system without a very through understanding. Time and time again, poor (but well intended) redesigns result in fuel supply failure. I share David's confidence in the standard arrangement.

[BillL]

Originally Posted by DanH

That's an old diagram. No current boost pump (Airflow Performance, Andair, or EFii) requires an external re-circulation line. Flow for pressure regulation is internal.

The line back to the tanks, as used with a purge valve or a Continental-style fuel injection, is an entirely different issue.

Last, do not redesign the fuel system without a very through understanding. Time and time again, poor (but well intended) redesigns result in fuel supply failure. I share David's confidence in the standard arrangement.

+2 - Stick with the standard. The electric pump is backup for TO when fuel, lines, under-cowl temps, and fuel flow (pressure drop) is most likely the highest, and would present the greatest risk to power interruption. It also can provide full flow in the sad event of a mechanical pump failure. Like Toolbuilder says, TO & landing and possibly (I don't understand the theory for this one) during a tank switch.

If you use auto gasoline, then it's necessity will be greater for same conditions.

I too, and quite satisfied with the Vans configuration. Oh exception: red cube (fuel flow meter) to be located between the servo and distribution block (spider)