Teeing Into Flared Fittings

[Zac Weidner]

I'm working on installing an oil pressure sensor on the Twin Comanche for an engine monitor upgrade, and trying to figure out the best way to tee into the oil pressure line for a sensor mounted in the engine compartment. I have Aeroquip hose with 491-3 flared type fittings on the hose between the accessory housing and the firewall fitting. The sensor I'm looking to install has a male 1/4" NPT. I can't seem to find a good fitting to make this work without taking up too much space and having to shorten the hose. The restrictor is built into the 90 degree fitting in the accessory housing, so I have to tee in behind that, and there's no room at the engine end of the hose for anything, let alone a wrench to get the hose installed. So basically I need something with a female and male flare on the straight part of the tee, and a female 1/4" pipe thread on the side of the tee.

Thanks in advance.

[Vagabondblues]

Assuming that your engine monitor system is redundant to the primary oil pressure indication, why don't you just put the oil pressure switch on the 1/4" NPT thread fitting on the main oil galley fitting on the front of the lycoming engine and just remove the need for a " t" fitting altogether?

[Zac Weidner]

The installation manual states that it should NOT be screwed directly into an oil galley as was the oil temperature probe. (Right front oil valley plug which is documented as Lycoming's pick for an alternative location). I can only assume, but I'd take it to be either because of the lack of a restrictor in this manner, and/or too much vibration directly on the engine.


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[Steve Pierce]

Every one I have seen had a line attached to the galley Todd referenced and the transducer attached to that. Which unit did you end up getting?

[Zac Weidner]

I don't remember those other ports being listed by Lycoming as alternate pressure-sensing ports, but only for temperature. Wouldn't the pressure be lower up there after it has a chance to drop out of that galley on the way to the front? I'd also have to come up with another restrictor in the new line that would be acceptable. Wick's had a fitting that would work, but I'm not comfortable with aluminum. I can't seem to find one in steel anywhere. It's a CC-303 which is a female 37° flare on both ends.
We ended up installing the Insight G4 Twin. Have been happy with it so far after only a few flight hours and getting the few bugs worked out. The amazing thing is that both engines had the CHT probe on the coldest cylinder. The right engine #3 is almost 100°F colder than the rest.


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[dgapilot]

Can you T in aft of the firewall in the nacelle?


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[andya]

A friend of mine installed a low pressure switch in the oil pressure line aft of the firewall. Not sure what kind of "T" fitting he used
but it apparently was not a problem. The pressure switch illuminates a warning light if pressure is below a given value (per the switch spec)

[Zac Weidner]

I've thought about teeing in behind the firewall, and there is definitely room back there so I could easily make that work. I just wasn't sure it was a good idea to have an opportunity for a leak back there where you don't inspect as often, and where a fire would be right on top of the fuel cells. Although there is probably a lot less vibration and harsh environment back there. Maybe I'm over thinking this, but I don't like the idea of a preventable fire.


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[andya]

Zack, off topic but preventable fires.
My line from the fuel distribution "spider" that goes to the Fuel Flow gage
was a solid line that went thru the baffle above the oil cooler using a
bulkhead fitting. It broke one day and the indication was EGT rising
and indicated FF decreasing. The line cracked and sprayed fuel on the
engine side of the baffling.

Lucky no fire. Replaced that line with steel braided hose so that will
not be a problem again.

FWIW