[PSUBS-MAILIST] thruster vacuum fill

[Jon Wallace via Personal_Submersibles]

I assumed Hank was suggesting the vacuum simply as a means of displacing 
air from the motor housing to achieve a complete filling of the cavity 
with oil.  How would you seal the motor in this manner after all the 
cavity is filled with oil and you want to remove it from the vacuum 
chamber...a one way valve perhaps?

Jon


On 3/22/2016 8:35 PM, Stephen Fordyce via Personal_Submersibles wrote:
> Hi guys,
> I've got a reasonable working knowledge of vacuum from being involved 
> with design and fabrication of vacuum-insulated pipes and vessels for 
> cryogenic fluids, and have a couple of comments on this:
>
> 1. I'm missing how it will help having vacuum in a pod when you are at 
> depth.  Ie. there is still a very large pressure on the outside trying 
> to get in (in fact, even more than if the inside was at ambient).
> 2. There's a potential benefit from vacuuming the pod before filling 
> with oil (ie. pull a vacuum, then release the vacuum with oil) as it 
> means there will be no possibility of condensation from any remaining 
> air, and oil will fill all the spaces where air might otherwise get 
> trapped.  Realistically, the amount of moisture you'd save from the 
> air would be pretty negligible, possibly the removal of airspace will 
> help with preventing water leaks from the outside.
> 3. Vacuuming the pod with oil or water in it may have weird effects.  
> Ie. water will boil (creating residue buildup from salt, tannins, or 
> whatever else was dissolved in it).  Oil will also evaporate/boil, to 
> a much lesser extent, but the thin oil typically used 
> for compensating will probably evaporate quite significantly under 
> vacuum for long periods.
>
> Cheers,
> Steve
>
>