[PSUBS-MAILIST] thruster vacuum fill

[Stephen Fordyce via Personal_Submersibles]

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


On Wed, Mar 23, 2016 at 7:24 AM, Alan via Personal_Submersibles <
personal_submersibles at psubs.org> wrote:

> Hank,
> the documents I gave links to on compensating systems, & seals for
> oil compensated deep sea systems, mentioned this.
>    It depends on what type of seal you are using & the orientation of them,
> as you can damage seals by putting a pressure on the wrong side.
> Have had those documents printed & bound:)
> Alan
>
> Sent from my iPad
>
> On 23/03/2016, at 8:56 am, hank pronk via Personal_Submersibles <
> personal_submersibles at psubs.org> wrote:
>
> Guys, I was wondering if anyone has looked at vacuum filling thruster
> motors.  I saw a tv program about building ROV's and that is what they
> did.  We could put the thruster motors in our pressure chambers full of oil
> and suck the air out.  That may be the solution to that pesky bit of water
> that gets in.
> Hank
>
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