Good O-360 FFW Fuel Line info

[Junglepilot]

For those like me with a non-certified parts built O-360 this Zenith site has some of interesting FFW fuel line routing photos you may or may not agree with.

Photos are OK, but mainly my interest was in the listed part numbers etc for O-360 specific fittings etc.

I found this very helpful.

http://www.zenithair.com/stolch801/d...el-lines-3.pdf

[osxuser]

That is pretty good. The biggest thing on the Carb'd Lycomings is to plumb the fuel pumps in parallel. The electric pump in the Van's kit especially is prone to clogging from small debris, and can make a really bad day if it restricts fuel flow too far. I also like that install, as it keeps everything (including the electric pump) forward of the firewall. The less fuel in the cockpit, the better in my opinion.

On an injected setup, they pumps have to be in series because of the higher pressures involved, unless you want to spend the extra money on some high quality check valves. The pressure on the outlet of the electric pump when it is turned off is enough to start fuel back-flowing through that pump and dropping the system pressure. The high pressure electric pump has a bypass built into it so fuel can be drawn through if it is plugged.

I always suggest a good quality fuel strainer such as Steve's:

http://www.stevesaircraft.com/gascolator.php

or Andair's...

[Walt]

Originally Posted by osxuser

That is pretty good. The biggest thing on the Carb'd Lycomings is to plumb the fuel pumps in parallel. The electric pump in the Van's kit especially is prone to clogging from small debris, and can make a really bad day if it restricts fuel flow too far. I also like that install, as it keeps everything (including the electric pump) forward of the firewall. The less fuel in the cockpit, the better in my opinion....

All I can say about this is that redesigning the Van's fuel system should not be taken lightly. I would caution anyone making such changes as noted above to proceed with extreme caution, and personally I do not recommend the above alterations! The only thing I do recommend is a prefilter after the fuel valve of 74 microns which is also recommended by Facet.

Originally Posted by osxuser

On an injected setup, they pumps have to be in series because of the higher pressures involved, unless you want to spend the extra money on some high quality check valves. The pressure on the outlet of the electric pump when it is turned off is enough to start fuel back-flowing through that pump and dropping the system pressure. The high pressure electric pump has a bypass built into it so fuel can be drawn through if it is plugged.

Sorry to disagree again but this is not accurate, either pump is 100% capable of suppling the required flow and pressure if the other fails. They are in series in both FI and carburator systems as designed for a reason and I caution anyone about redesigning the fuel system without EXPERT advice.

Looking at some of those install examples on that Zenith make me cringe !!!

[Junglepilot]

Hey on the parallel pump set up do you have any photos or diagram of such a set-up? Where does the parallel plumbing occur exactly?

[DanH]

Originally Posted by Junglepilot

...this Zenith site has some of the best FFW fuel line routing info which should for the most part transition to the RV program.

I'd suggest the line from electric pump tee to engine pump inlet is a bit short.

The line to the carb is zip-tied to an engine mount tube about 6 inches from the carb....too little slack; something is going to be sawed.

The mixture cable is attached to a motor mount tube with a pair of adels....when the engine shakes due to torque reaction the mixture lever is going to move with it. The shaft into the carb will wear out quickly.

[osxuser]

Originally Posted by Walt

Sorry to disagree again but this is not accurate, either pump is 100% capable of suppling the required flow and pressure if the other fails. They are in series in both FI and carburator systems as designed for a reason and I caution anyone about redesigning the fuel system without EXPERT advice.

Looking at some of those install examples on that Zenith make me cringe !!!

Yes either pump can supply full pressure, I made no claim otherwise. IF the high pressure pumps were in parallel, AND the electric is turned off, the pressure from mechanical can bleed back through the electric, and thus reduce the total system pressure to lower than acceptable. That is why certified aircraft FI fuel systems are in series.

As for the low pressure pumps being in parallel for a carb'd setup, most if not all certified airplanes are set up this way. Van's setup is actually the anomaly here.

Check out the fuel diagram in this Cherokee 180 flight manual as an example.

http://www.freewebs.com/defence_aero...el%20PA28E.pdf

Fuel systems should be modified with caution, but I've had experience with an RV-6 that had a partial loss of power due to the Van's design, that would've never had that problem if they had been parallels. It's a pretty small modification all things considered, you don't have to change the routing of anything, just mount the pump to the firewall, and use a T at the inlet of the electric pump and at the inlet of the carb.

And I also think that we can all agree the craftsmanship on the Zenith isn't A+ work, hopefully that was just testing, not flying that way. I don't see the mixture as being a problem honestly. Once again, that is pretty standard with certified airplane, and I don't see them wearing out carb mixture shafts often... I think I've only ever replaced one, on a Cessna 150. The should have a wire type control on it though, not the stiff shaft type, that would probably absorb more vibration.

[rocketbob]

Actually the fuel system design in the pdf is p***-poor. If one of the two diaphragms in the mechanical pump ruptured and failed open, there would be no way for the electric pump to pressurize fuel going to the carb...it would just recirculate.

If the check valve in the Facet pump failed....it would also cause a lack of pressurization.

[osxuser]

Bob, I respectfully disagree. I've seen a diaphragm fail, and the electric kept up just fine. I've also seen the Facet get plugged on an RV, which the mechanical couldn't do anything about. The pilot was lucky to make it around the pattern and land.

Once again, I reference the way certified airplanes do it... there is a reason they do it that way. I suppose a catastrophic failure of the mechanical could induce enough of a problem that pressure might drop. But remember, all you need is 3 PSI at the inlet of the carb with some volume, and you are fine. The problem with the series setup is the failure mode doesn't provide for any volume.

[airtractor8]

No one has mentioned the use of an aluminium fitting on the carb inlet shown in the pdf...a BIG no no, should be a steel fitting. Thought you guys would have picked that one up straight away.

[L.Adamson]

Originally Posted by airtractor8

No one has mentioned the use of an aluminium fitting on the carb inlet shown in the pdf...a BIG no no, should be a steel fitting. Thought you guys would have picked that one up straight away.

I picked it up right away, and mine is steel (because of the location). But there are those who say that every fitting should be "steel" firewall forward...... including the fitting on the firewall. Mine are not.

L.Adamson --- RV6A