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Old November 1st 04, 07:42 AM
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Default Attn: Hydraulic experts - oil pressure relief fix?

Okay, here's the deal. Lycoming O-320 in a Glasair. On full power, whether
oil is hot or cold, oil pressure will be higher than the regulator is set for.
(Shoots to top of yellow arc - 90 psi. I think all Lyc's do that.) Upon power
reduction, say turning downwind, you can "see" the ball jump off the seat when
the oil pressure gage goes "sproing" and the pressure suddenly drops to the
regulated 60 psi in a classic 2nd order damped sinusoidal response. It will
stay at regulated pressure until the ball seats itself again, say on final
approach with the engine at idle where the pump isn't making as much pressure.
Then the process starts over again, on the next touch 'n' go. I'd like to have
regulated oil pressure all the time.

I'm theorizing that there's some kind of venturi effect, where the ball is
actually sucked down harder on the seat when lots of oil is flowing past it on
the engine side. Seems counter-intuitive, I know, but what else could be
holding the ball down?

Anyone got a simple fix I can try? Larger ball bearing? Smaller ball bearing?
Cutting groves in the seat to help ball break free? Different angle on the
face of the seat?


Mike Palmer
Excellence in Ergonomics