Re: [PSUBS-MAILIST] Pressure calcul

[Ian Roxborough <irox@ix.netcom.com>]

On Wed, 05 Feb 2003 17:57:26 -0500
"Pierre Poulin" <pipo305@hotmail.com> wrote:

> 
> Hi,
> 
> I forgot who said the last word about calculating the water pressure but I 
> think that you don't have to had the 1 atm from air into the calcul because 
> the interior of the sub is at least at 1 atm. Those 2 pressure negate. So a 
> sub at 33 feet will be under 15 psi.

Your right.

At 33 feet the pressure difference between the inside of a 1ATM sub and the
external water will be 15 psi.  But the water pressure on the surface of the
sub will be 30 psi (water pressure + air pressure action on the surface of
the water).  This is the difference between the 'actual pressure', and the
'gauge pressure' (gauge pressure = actual pressure - air pressure).

If the gas in your sub cools then the pressure will drop, increasing the
gauge pressure with no change to the actual pressure.


Ian.