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!

[Grant4ever]

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!

I just like reducing the fuel line breaks in the cockpit and these filters I found were clear plastic body with sintered bronze element. I prefer metal case firewall forward.

[wapelhj]

Here's my two cents. If the engine will run without the engine pump no aux is needed. If not you have to eliminate any single point of failure and the series mounted electric pump is the answer. Some engines will not run if both pumps are running at the same time.

Filters? I remember gascolators that were just a screen and a drain for any water. My V-tail Bonanza just had a screen in the bottom of the fuel selector and that was on a fuel injected engine. KISS and buy clean fuel and skip the filters(your choice of course).

[n85ae]

Story time it is:

I remember back to test flight #4 behind my stopped IO-240B at
3000 ft. trying to decide if it was the Golf Course, or the Airport for
landing ...

I decided TWO things, (1) Having a backup pump is an excellent idea
(2) Having a BIG enough backup pump to actually run an IO-240B is an
even excellent'er idea ...

A Facet (as suppplied by Skystar) is nowhere near enough pump to run
an IO-240B

N85AE has a really expensive Weldon backup pump now, AND yes IO-240B
fuel pumps actually do fail, which means ... Yes your pump can fail also.

Been there done that :)

Jeff

[Av8r3400]

FYI: The mechanical pump on a Rotax 912 has a fine screen on the intake side. This is a non-servicable filter (without a ton of monkeying around).

I have no aux pump on my flying plane and never have felt the need for one.

I did add a Facet pump just down from the header tank on my project plane. The flow will go from the header to the aux pump to an inline filter to the mechanical pump then to a flow meter then to the carbs. The mechanical pump will flow through without need of bypass in the event of failure.

In our Kitfoxes gravity will flow fuel in the event of a mechanical pump failure. The pitot tubes on the fuel caps will also aid in providing a positive flow.

The main reason I added the aux pump to my project plane was to aid in cold starting. A friend has this setup and it makes the cold start (refilling the carb floats) much quicker. The process goes: turn on the pump until you hear it change pitch (float bowls full) then he shuts it off and proceeds with the engine start.

[n85ae]

Nice theory, but not true in all Kitfoxes. Certainly not mine ... :)

Jeff



In our Kitfoxes gravity will flow fuel in the event of a mechanical pump failure. The pitot tubes on the fuel caps will also aid in providing a positive flow.

[Av8r3400]

Being fuel injected this wouldn't apply to your IO240.

I should have qualified that statement! My bad.

[kitfox2009]

Hi guys
This may seem foolish to some but I fly a Vixen with 912UL, no fuel filters,gascolator with fine screen,use non ethenol premium marked off highway fuel except when traveling and 100ll only available.
In 600 hours I have never had a fuel starvation or contamination issue.
I replaced the fuel pump at around 400 hours. New pump with overflow drain line.
So far very satisfied with the results.
Don

[Planesmaker]

Hi guys
Beware thinking fuel will always gravity flow through a failed mechanical pump. Just had a customer have a pump failure ( new style pump only done less than 40 hrs). Fuel would not gravity feed through the pump! There was no auxiliary pump! Safe landing carried out in a paddock. Even when pump was bypassed, gravity feed was marginal on climb out, could only manage very shallow climb. This was not a kitfox but still a high wing 912 aircraft.
My advice is to have an elec backup in series with mech pump.
Tom