Re: [PSUBS-MAILIST] K250 to K400 modification

[Jon Wallace <jonw@psubs.org>]

Sorry Alan, I missed the "emergency situation" part.  So yes, in an emergency where you are sinking in water beyond your normal operating depth you could certainly counter some amount of outside pressure by increasing the pressure within.  That may delay (possibly prevent depending upon depth) hull failure but of course has the potential for some other nasty biological side effects and I'm guessing in such an emergency you're probably going to be at the increased ambient depth well beyond no-decompression limits.  We had a similar discussion a few years ago about standardizing on a specific valve so that divers could feed air into the cabin of disabled sub that did not have life support capability, until that sub could be raised.  I believe the discussion started with "schrader" valves (tire valves) which were determined to be too small to be useful.  Many of the same issues were raised at that time ie...decompression upon surfacing, additional pressure in the cabin affecting instruments, etc.

Jon


On 7/4/2010 12:29 AM, Alan James wrote:

Thanks Hugh & Jon for the vote of confidance.

I did qualify this with " In an emergency situation". I think I have been misunderstood.

You take your sub down to its 250ft limit with several extra dive tanks on board.

At this point the outside of your hull is experiencing round 125psi.

For every 33ft further you go down you add 14.7psi. The hull would always be experiencing

125psi from the outside as the pressure you're adding would be countering the additional

pressure from additional depth.

So no pressure as such from the inside would be pushing your view ports out.

The reason I said to increase the O2 flow into the hull is the "bellows add" system based on

sensing a drop in pressure wouldn't work. In that system the O2 flow is set below the users

normal O2 consumption & then topped up from the bellows add system because if the O2

was set too high there would be a continual pressure build up & 02 % increase.

You could safely bump up the O2 a tad as it would be safer to have too much O2 than not

enough. This, as Jon said wouldn't matter much because your time would be constrained by

decompression tables, & there would be enough air in the hull to breath from.

So in a life or death emergency you could take several air tanks into your hull & a set of

dive timetables, open the tanks by hand at the 250ft mark & go to 400ft.

Alan