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Finally got that 737's persistent bleed air leak sorted after three days of chasing ghosts.
Turns out the O-ring on the precooler control valve was just slightly out of spec, something you'd miss unless you pulled the whole assembly in Dallas. We replaced it with a fresh one from the kit and the pressure held perfectly. Ever have a gremlin that was just a simple part wearing out a little early?
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margaretf401mo ago
Weird how something so tiny can cause that much headache. Did you check the torque on the bolts when you put it back in or just button it up?
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the_amy1mo ago
Just cranked em down till they felt snug and called it a day lol. Learned that lesson the hard way a few years back though. Had a buddy who torqued everything to spec and still had the same leak because that backup ring was twisted like a pretzel. Spent like 3 hours pulling it all apart again just to fix a 5 cent piece of plastic. Tiny stuff like that always comes back to bite you when you least expect it.
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the_luna1mo ago
Oh nah, torque on those bolts is kinda forgiving actually. The real trick with those pre-cooler valves is making sure the Teflon backup ring isn't rolled when you seat the new O-ring. If that ring is twisted even a little it'll let air bleed past again within a few cycles.
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