Re: [PSUBS-MAILIST] Hatch pressure

[MerlinSub@t-online.de]

Hi Alan your english description is not complete clear for me. Sorry for that. 

During dive a 1atm. submarine down the hatch is hold by the dogs. 
If the oring seat is uneven - it is maybe a little untight on the first feets 
before the waterpressure press it down and tight. 

The problem is more if you come back to the surface. 
Special if you have an air leak from a internal pressure pipe or bottle or to much oxygen or/and carbon dioxide pressure in the cabin. Or the outside barometic pressure is much lower than as during start the operation.
Or you have a waterleak in the boat - which also raise the cabin pressure.

The dogs should hold this additional overpressure - otherwise - in case off for example no dogs, dogs open or rubber dogs it is possible that the hatch will open by this force with the boat still 1-2 feet under water. 

A overpressure vale will help to prevent that. And never open the hatch after a long dive allready surfaced before you have open the small ball vale or the release trigger on the overpressure vale to equal cabin and outside pressure. 
Otherwhite the hatch can open very fast with maybe damage to your ears.

If you have a hatchframe with a dome on top and the dome acryilic is just glued to the frame it is absoult recommend to have an overpressure vale in the pressure hull. Otherwise the acryilic itself can pop out of the frame trench with the frame still sealed on the oring seat.. 

vbr Carsten "Submarine are easy - in principle.."


Alan James" <alanjames@xtra.co.nz> schrieb:
> Hi all,
> I've brought up this subject before, but are tackling it from a differant angle.
> How much pressure is exerted upward on a hatch at the moment where the submarine
> just submerges below the water? This is the point of most force before external water
> pressure helps close it.
> If you took your submarine, filled it with water & hung it upside down, would this be the
> same amount of force, or close to it.
> In wich case if you have a design like Franks flying saucer that angles up to the hatch,
> you'd have a lot more force acting upward on the hatch than a K250 where the lifting force 
> would be spread more evenly along the hull.
> Am I thinking right?
> Alan
> 




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