When a jet engine is running, it's generally immune to any liquid in the incoming air as the liquid would have been evaporated in the compressor. However, when the engine is being cleaned for carbon deposits, cleaning solution mist is injected is fed to the inlet, and the water would have the chance of entering the compressor bleed. Is there any special design in the bleed path to keep the water out, or the water simply couldn't get past the labyrinthine seals around the bearings?

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    $\begingroup$ "the liquid would have been evaporated in the compressor" uhm, considering we are talking about adiabatic compression, that's not a given. you can liquefy gases by compressing them. sure, the temperature rise would work against that. $\endgroup$
    – Federico
    Jan 25, 2019 at 14:46
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    $\begingroup$ How do your car's wheel bearings keep water out when you drive in the rain? $\endgroup$
    – jamesqf
    Jan 25, 2019 at 18:30
  • $\begingroup$ Bearings are not exposed to air, they need to be lubricated and oil has to be in a closed space (sump), see How does a labyrinth seal work when the engine isn't rotating? $\endgroup$
    – mins
    Jan 25, 2019 at 21:42
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    $\begingroup$ @jamesqf Car bearings are self-contained and do not circulate its lubricant in an open loop or intentionally mix its precious lubricant with ambient air, nor do car bearings rotate at 10,000 rpm. $\endgroup$ Jan 27, 2019 at 7:04

2 Answers 2


To keep dirt out, bearings with exposed faces have rotary seals on them. Those seals will also keep water out, as long as the bearing is not rotating when wetted and not completely immersed. If immersed for days or weeks, even well-sealed bearings will eventually allow water in.


Water is kept out because the oil is supplied to the bearings at a higher pressure than the surrounding air, so the oil mist is blowing away the air, not the other way around.


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