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Jeff if you're installing a Lyc O-235 you do not need a fuel pump on either the engine or electric, gravity will work perfectly. If you want a pump anyway I would opt for the electric since you can control it, whereas an engine mounted pump is always on. I'm actually not sure that if you have an engine mounted pump and it failed that gravity would be able to take over (you'll have to research this with Lycoming) and in that case you would want an electric back up. Easiest would be gravity but no harm in adding a Facet pump like the one that Joe Spencer uses...40108, that will allow fuel to flow even if it fails.
The previous comment about always needing a check valve would apply only to certain specific engine installations and would not apply to a Lyc O-235.
Agree with Don.
Here's some info from I think it was Tony Bingelis.
>>>Just keep this in mind. A failed engine driven fuel pump can create a serious fire hazard if the diaphragm ruptures and if the vent has not been connected to a line routed away from the hot exhaust pipes to a safe overboard location. Furthermore, the engine won't run any more . . . not without the help of a back-up fuel pump.
Such an auxiliary pump can keep your engine running even with a failed engine driven pump. This is possible because the AC type engine driven fuel pumps (and the Thompson and the Romec pumps as well) have an internal bypass valve that allows the fuel to flow through the engine driven pump even after it has failed./p>
Obviously he's talking about a non gravity system but the main points still apply.
IIRC the straight thread inlet/outlet fittings for the pump have a significantly smaller I.D. that the 3/8 line. Not only what Tony said above but I wouldn't want any restricted I.D. fittings. I may remembering that wrong...somebody correct it if so. And the Lyc pumps are heavier than the Facet. I definitely wouldn't want that pump on my plane
>>>The previous comment about always needing a check valve would apply only to certain specific engine installations and would not apply to a Lyc O-235.
Agree. I think many of us realize that but Bob spoke with such authority about needing a check valve that it sounded like he may know something the rest of us don't. Apparently not, since he hasn't told us what that might be. Along with his statement that all the Facets have a failure prone check valve and 1/4 ports. Looks like all that has been cleared up by the info we've been able to dig up.
I think valid info is what we're all after.