Re: [PSUBS-MAILIST] K250 to K400 modification

[MerlinSub@t-online.de]

Hi Alan - In General you can go that way. 

A sub designed for 150 ft max dive deepth can double there operation depth with that way. 

The only real problem is if the boat is in this condition and you pop up (surface fast).  

There are two possible failtures: 

- Overpressure vale to small and hatch and windows pop out.

- Over pressure vale has the right huge size and crew gets heavy decrompression tickness, blown ears etc.. 

- In case of a fire or anything else in the sub - you can not surface in short time and probably get problems in it. 

We discuss this way some years ago but never go this way. 
Its a way only for crew with real expierence with there sub and also real scuba divers with expierence with decompression dives. 

If you double the cabin pressure just with air this means you double the amount of o2 atoms per volume. 
The fire risk increase.. If you increase the pressure with helium this will work. The problem starts than when you lower later the pressure - you have to feed o2 back. 

By the way what shall a K250 do in 400ft on a stricken sub? 

vbr Carsten


"Alan James" <alanjames@xtra.co.nz> schrieb:
> Hi Jon,
> The emergency I was thinking of was along the lines of
> a stricken sub entangled at 400ft & the nearest help was
> a sub capable of 250ft depth.
> Alan
>   ----- Original Message ----- 
>   From: Jon Wallace
>   To: personal_submersibles@psubs.org
>   Sent: Sunday, July 04, 2010 5:41 PM
>   Subject: Re: [PSUBS-MAILIST] K250 to K400 modification
> 
> 
> 
>   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
> 
> 
> 
> 




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