O-540 Fuel pump

[zkelley2]

Finally got around to doing my fuel flow test today as per the AC. Flowed 31gph from the left tank, 25 gph from the right and 32gph from both. No fuel pump.

Since that doesn't quite meet the 35.75gph they want from a gravity system I'll be installing pumps.

Funny that with a pump it gets the gph at 125% without the pump.

[jaredyates]

Reviving the old thread here, I need to replace the Facet pump that goes in series with the engine driven pump. But I'm confused about the check valve. The existing pump has a little ball that acts like a check valve. The Vans folks seem to run without check valves. Has anyone gotten to the bottom of what the ideal arrangement is here?

(edited to add)
After googling enough to make my eyes bleed, this is what I've gathered so far.
The Facet pump that I'm removing is a 40108. This is a pump that has 3/8 37-degree flared fittings molded onto it permanently. Facet decided to do us a favor and discontinue that pump. While the pump does have a little white ball inside that acts like a check valve, apparently they don't consider this pump to be a check valve pump. If you blow into one end, nothing comes out. If you blow into the other end, it flows freely. But that's not a check valve.

The Vans folks are recommending a 40135 pump, and adding AN818-6-2, which is a nipple fitting with 1/8 pipe threads on one end and 3/8 flare on the other. The only problem with this is that now the fuel system is going to have a 1/8" flow restriction instead of the old 3/8. They say it's good to about 150 horsepower, but it is rated for 32gph flow. The flow varies with the pressure but I haven't been able to find out how yet.

In the cube-type Facet pumps, it looks like there is only one model that has anything bigger on the inputs. The 40109 has 3/8 pipe thread inputs, which is great, except that this pump has a check valve.

Maybe there's a better option for carbureted boost pumps than these facet cubes?

[zkelley2]

What do you see as the downside to the checkvalve? In our application, at least off the top of my head, it doesn't seem like it'd matter one way or another.

[jaredyates]

The only thing that worries me is that the check valve might reduce the flow rate when the pump is off. But I don't have data to support this yet.

[Battson]

jaredyates you asked about possible alternatives.
I used an electric pump made by EFII to supplement the engine driven pump (which is a diaphragm pump in my case).
The EFII pump has a large bypass built in with a check valve, and they claim it offers very low resistance to fuel flow. But it does require a fuel filter, and the resistance to flow all adds up.
It is not small by any means, and retrofitting it may be somewhat involved - but no problem for an experienced builder.

[jaredyates]

Thank you Jonathan, do you run it all the time or only for low altitudes? I have ordered a couple of different Facet cubes to study the check valve situation.

It looks like the EFII pump puts out 30 psi which would not be compatible with the carb, but probably a nice option for fuel injection.

[Battson]

Ahh - I was not aware of that requirement.
We only run the boost pump during critical flight phases, near ground, or (rarely) when changing tanks.
Interestingly, while the pump is rated to 30psi and the engine driven pump develops around 25psi, if conditions are right the pressure in the fuel lines can exceed 40psi while priming before a hot start. I try and depressurize the lines when this occurs, by allowing fuel to flow through the servo briefly.

[Rollie]

Hey Jared, I'm running the Airflow performance fuel pump and it seems to work great. Not sure if it will work with your set up but might be worth checking out.

[zkelley2]

The only thing that worries me is that the check valve might reduce the flow rate when the pump is off. But I don't have data to support this yet.

I'll look at what facet pump I'm running when I'm at the airplane next. I can't remember the exact model number, but I suspect it's the same one you're replacing. I know facet is not happy about how much their pumps are used on aircraft, so it doesn't surprise me they discontinue the best one for aircraft. If none of the current facet pumps work, I guess 1/2" lines are always an option.

Hey Jared, I'm running the Airflow performance fuel pump and it seems to work great. Not sure if it will work with your set up but might be worth checking out.

That runs too high of pressure as well. Carb aux fuel pumps should run 5-7psi.