Installing a standby Electric Fuel Pump

[Cloud Warrior]

DH - I have been told that the mechanical pump cannot handle more than 2-3 bar pressure on it from the Facet pump. I have since discovered that there are several different models of facet pump with some of them being able to supply up to 9 bar pressure. The kit that I got from the auto shop is the 40242 kit which contains the pump as well a two hose fittings. The pump itself is the 40105 model which only delivers about 3 bar so should be fine for this application. Just check the small print on the box - the pump might end up doing more harm than good!

[DarkHelmet]

The only thing on the box is 50106N - cannot see it on the spec sheet, that is why I posted the link - Have not had too much time to hunt for more.

Cannot see any ID on the unit either - how heavy is the one you got? Also 2 brass hose fittings

Tearing the 50106N off I see it is a 40242 box but that says nothing - eek...

No ID on the unit ...

[Morph]

I've only ever seen one size. I have no idea on the weight but the size is about 40mm by 50mm by 50mm, It has a black, negative to earth and two brass fittings.

[Cloud Warrior]

That's the problem - they all look the same but some of them are more powerful than others. If the box says 40242 then you should be fine. That is a kit which contains the 40105 pump and the brass fittings. 40105 pump pressure is 2.5 - 3 Psi. There are no actual markings on the pump istelf except that it is 12 v (there are 24 v models as well) - not very clever if you ask me.

[ACE]

The best was Big-G, engine cut 14 Km from the neastest strip in the berg, and he managed to glide back from 12000 ft

I figure this is how Big-G(lide) got his nickname

[Morph]

I like that fuel filter you have fitted too morpheus - what is it called and where can it be found?

I had a good look at the fuel filter and all I can see is Made in Italy and the manufacturer is 'Malpassi Seregno'

[DarkHelmet]

w000t - The filter I have seems to be a 40105 - I was about to mount it and noticed the number on the mounting plate! The other footplate is marked C 05....

[DarkHelmet]

Bump an old post - but this is relevant

I have installed my pump but after convo with PastMaster we think it might be better to split the fuel pipe at the tank, into the two pumps and then join again?

Any thoughts?

We would need to source 6mm Y-splits for the fuel line, preferably stainless steel - anyone know where these can be found?

[Morph]

DH,

there are many different thought processes on this and one consensus is that running parallel systems adds unnecessary complexity to the entire system. It also adds additional piping and joints that could introduce problems. The electric fuel pump is a free-flow device, so of it is not running the fuel passes through it easily. All the planes I know of except one have it in series and it works like a charm. Whether you put it before or after the fuel filter is a moot point.

Your average Midas should have all the joints you would need.

One of the guys at our airfield needed it comimg back over the Franschoek pass where the engine started coughing at the worst time. Everytime he switched it on the engine note came back to normal, causing him to switch it off again. He had to do this 10 times before reaching the airfield. I would have left it on. Anyway the point is that after replacing pipes, servicing the pheumatic pump and carbs it was found that the breather hole in the top of the tank still had the little plastic burr on from when it was drilled. The sucking of the air would cause the burr to close the hole and starvation would occur. The electric pump saved him here. BTW this is in series.

Don't overcomplicate things, go in series, it works perfectly.

[Aviation Engines]

Morpheus,

Well Done! and I must say that you have installed and wired it very professionally,

May I use your wiring diagram for training courses? I'm not a regular "Picasso"

I would also like to add that electric pumps must always be installed in series to the standard Rotax fuel pump and NEVER in parallel.

The efftive pressure of the parallel installation is the sum of both pumps, however the effective pressure in a series installation is equal the maximum pressure of one of the pumps.

The auxiliary pump should only be used during take-off, landing and emergency situations.

Regards
Niren

[Morph]

Morpheus,

May I use your wiring diagram for training courses? I'm not a regular "Picasso"

You're welcome to use it anytime Niren

[Abe]

Hi Niren and all listening,

Maybe you would like to rephrase that? No offence, but it takes awhile to get up to speed coming back from vacation?
You said "I would also like to add that electric pumps must always be installed in series to the standard Rotax fuel pump and NEVER in parallel."

Please motivate? For true redundancy the pumps would have to be in parallel, with seperate fuel filters. The Mikuni pulse pump standard to Rotax 2-strokes is one-way free-flow at low pressure through two reed valves if unoperational, but many electric fuel pumps are positive-displacement or have formidabable springed valves that if not working will leave the pulse pump gasping. A parralel electric pump will continue fuel supply if at least one of the valves in the Mikuni pump is still more or less resisting on overpressure.

Then you added: "The efftive pressure of the parallel installation is the sum of both pumps, however the effective pressure in a series installation is equal the maximum pressure of one of the pumps."

My logic says the opposite? (But OK, an ambient-pressure powered pulse pump will not add pressure, just sit on the sideline if overpowered.)

Best regards and fly safe, you all!
Abe

[Pumba]

All

In deciding on whether to install the electric pump in parallel vs series with your Mikuni diaphragm pump, it is crucial that you understand how both pumps are likely to fail. If either of them shuts of closed when it fails it creates a blockage in the line and renders the other pump absolutely useless, and the right way of doing the installation is to have the pumps in parallel. This way, a failed pump will only block of one line, and the functional pump can continue supplying through the other line.

If the pump fails to the "open" position, you need to have them in series as the functional pump can continue supplying fuel straight through the failed pump. With parallel pumps you create return to the tank that may jeopardize the correct functioning of the system as the fuel flow will always follow the easier route, and it may starve the carbs.

Niren, your statement that pumps in parallel will supply the sum of the pressures delivered by both, and pumps in series supplying at the pressure of the highest pressure producing pump is wrong. A study of Hydraulics or Fluid Mechanics will tell you that theoretically parallel pumps supply twice the volume at the same pressure while series pumps raise the pressure to the sum of both pumps. In practice, this does not materialize and is dependant on a whole bunch of factors.

As it happens, the Mikuni fuel pump will most likely fail in the open position as it contains 2 small diaphragm valves, but you need to take a carefull look at the electric pump you intend to use. If its one of the types that you can look right through, it will fail open. If it contains spring loaded valves, its likely to fail closed.

I once experienced an engine out caused by an outboard engine primer bulb that I had installed in the fuel line on my trike to facilitate easier starting. These things have 2 little plastic one way valves in them, and the one got stuck into its seat. Anyone who has these installed, please ensure you have a bypass line installed with "tee" pieces before and after the primer bulb. I was told to buy a good quality bulb to ensure that it is reliable, but that's not good enough.

[Morph]

The Facet pumps are straight through pumps with no valves. Most of the time the pump is switched off (thus simulating a functional failure in a way) and I only switch it on in an emergency, when neccessary. The Mikuni sucks fuel through the switched off electrical pump with out any problems. My plane has 530 hours on it and in the last 350 hours (previous owner and myself) it has never had a fuel starvation problem from the electric fuel pump inhibiting the fuel flow while switched off. The mikuni has had a few problems where old electrical has saved the day. I personally have had to use it once in the last 120 hours due to a clogged fuel filter and and it saved my bacon. Well worth it


So if you are installing a Facet Pump, it must be in series. Other pumps, using valves that restrict the fuel flow when off should be in parallel but I believe this is far too complicated. Keep it simple

[Pumba]

To those of you who are interested in the fuel filter as can be seen in Morpheus' original post, check out this website. I do not know if they have agents in SA, but it may be worthwhile e-mailing them and finding out. Its all in Italian, but easy enough to follow.
http://www.officinamalpassi.it/

It sure looks like a worthwhile investment.