Aux fuel pump revisited - aargh, what to do?

[Grant4ever]

I have a Series 7 that was built with an aux electric fuel pump. The aux pump was plumbed in parallel to the engine driven fuel pump

The addition of the aux pump complicates the fuel system by adding -

One electric fuel pump.
Two check valves.
An electrical circuit for the pump.
12 additional fuel line breaks secured with hose clamps.

Yes, I gain the redundancy of an aux fuel pump but I feel like that is somewhat offset by the more complicated system and potential for leaks/fires.

I have given serious consideration of simplifying the system with engine driven fuel pump only or by plumbing the pumps in series to eliminate the need for check valves and reduce the number of fuel line breaks by 8.

Having poked around the internet and read old posts here, I was looking for any additional input on the subject that anyone may want to add.

Thank you.

[N981MS]

Which engine do you have.

Our fuel injected IO-240 requires a pump to start the engine (So I am told. I never tried without one) so why not have one that will run the engine if needed.

[Paul Z]

I only have one fuel pump but I am contemplating putting in a electric fuel pump as a back up. It is a trade off of more complexity, & safety. I personally would keep it and check the fittings for leaks, inspect it annually, and replace the hoses every 5 to 6 years.

[kmach]

I like the redundancy of the electric pump.

On my model 5 , 912 ULS , I have from the firewall connection , a fuel filter, the facet square electric pump(I believe 2.2 - 4.5 psi), fuel flow sensor , this then connects to the mechanical pump "IN".

This is all in a line ,NO check valves or parallels.

I turn it on in the preflight checks, fuel pressure rises, as does the fuel flow.

I also have it on for TO and climb out . cruise OFF . On for landing in case of a go around.

[HighWing]

My system is similar to Kevin's but the inline pump is just after the header tank. When I built my first IV, I hired a guy to do the first few flights and he recommended pump on at takeoff. I did that for a while, then stopped mainly because at that time very few 912 owners had the aux pump and I don't ever recall anyone having an emergency due to mechanical pump failure. And that impression persists today. I personally did use the aux pump once on TO because I had unknowingly over tightened a firesleeve clamp that reduced fuel flow resulting in poor engine power. My switch is on the thumb side of the throttle and the pump was on instantly.

I certainly respect the redundancy idea but complexity can sometimes introduce failure modes as well, as has been suggested - My reason for using oil cooler shutters vs. an oil thermostat. Though I do use a coolant thermostat with an internal bypass. The internal bypass again to reduce complexity.

[TahoeTim]

I am curious to know if the engine will run with at least partial power without the mechanical pump. I guess I could destroy the diaphragm in an old pump and test the theory that it will continue to run.

Hal Stockman sticks a fuel filter on the high pressure side only. His theory is that he can see the pressure start to drop as the filter gets plugged.

[kmach]

Hal Stockman sticks a fuel filter on the high pressure side only. His theory is that he can see the pressure start to drop as the filter gets plugged.[/QUOTE]

Isnt part of the reason to have a fuel filter , is to ensure clean fuel goes through your pumps , mechanical and electric , as well as the fuel flow sensor to reduce wear and problems ?

[TahoeTim]

agree 100% with you, I was just letting everyone know what an engine builder does on his personal plane.

I have almost decided to install two fuel filters at the inlet to the header tank. That way if one filter gets plugged, the other wing can feed the header tank AND I will possibly see the fuel drop in one wing and not the other (don't know if they will balance out too fast to see the imbalanced flow).

[Grant4ever]

agree 100% with you, I was just letting everyone know what an engine builder does on his personal plane.

I have almost decided to install two fuel filters at the inlet to the header tank. That way if one filter gets plugged, the other wing can feed the header tank AND I will possibly see the fuel drop in one wing and not the other (don't know if they will balance out too fast to see the imbalanced flow).

I just deleted two in-line fuel filters (one from left and one from right) that were just before the header tank. I didn't care for the fuel line breaks and potential for leaks in the cockpit.

I'll be filtering firewall forward.

Failed to mention yesterday that this is all on a Rotax 912.

I have decided to replumb the Facet electric aux pump in series with the engine driven pump. Doing so simplifies the current parallel setup which eliminates the two check valves and only adds 4 additional fuel line breaks. Not much more complex with fuel pump redundancy.

[TahoeTim]

interesting on the filters. You are only adding one additional connection since you have one connection to the header, no matter what. I looked at filters with AN fittings but I haven't decided on anything yet. Heck, I haven't even figured out what micron sizing is best!