Patrick,
As the question is specific to an ambient dry sub which is my design profile, I will answer you in that regard. Whereas a semi-dry or open ambient has a direct connection to the outside ambient pressure, to remain a truly dry ambient requires the use of check valves.
The pressure is equalized by a constant flow of air introduced into the cabin which opens the check valves and dumps the overpressure outboard. The outside ambient pressure does not directly impact the cabin as you noted. There is a delay in compensation, which limits descent rate to design structural capability.
To oversimplify the 1 atm vessel keeps the pressure out by the brute force of it's designed structural integrity.
Joe
From: "Patrick" <pat_man_ta@hotmail.com>
Reply-To: personal_submersibles@psubs.org
To: <personal_submersibles@psubs.org>
Subject: [PSUBS-MAILIST] Ambient / 1ATM Q?
Date: Thu, 19 Jan 2006 11:21:48 -0500
I am having some trouble wrapping my head around HOW the outside pressure influences the inside pressure in an ambient dry sub and how a 1ATM sub keeps the pressure out. Could someone explain this to me?-patrick