[PSUBS-MAILIST] thruster vacuum fill

[Sean T. Stevenson via Personal_Submersibles]

The procedure in the linked document doesn't alleviate the need for volume compensation, but rather seems to be employed for the purpose of degassing the compensating oil (driving out dissolved oxygen), or replacing any such oxygen with nitrogen, prior to proper compensator fill and placement into service. I'm not sure why - perhaps the dissolved oxygen contributes to corrosion in the motor?

Sean


On March 23, 2016 9:22:00 AM MDT, Jon Wallace via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>Hank, another question on this procedure...with the cavity filled with 
>oil don't you still run into the issue of fluid expansion due to 
>temperature rise either through operation or sitting in the hot sun for
>
>a few hours?
>
>Jon
>
>
>On 3/23/2016 11:17 AM, Jon Wallace via Personal_Submersibles wrote:
>>
>> 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
>>>
>>>
>>
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