Hi, Joseph . . .
Short answer: the cabin is at less pressure
(partial vacuum) than the surrounding water. Greater pressure outside
pushes in on the reg's diaphram since the lesser pressure is on the mouthpiece
side. Essentially the cabin is like your lungs: drawing in
air.
The regs will be mounted on the bulkhead with the
diaphram on the water side and the mouthpieces on the cabin side.
I had a long answer but the short one
works!
Rick L
----- Original Message -----
Sent: Friday, January 20, 2006 7:17
AM
Subject: Re: [PSUBS-MAILIST] Ambient /
1ATM Q?
Rick wrote:
"I'd like to add to this by saying that a semi-dry ambient can also
use this system. How? Once the required amount of
ballast water is admitted, you seal off the cockpit so that the regs take
over. Open the valve, the cabin is exposed to surrounding water and the
regs are disabled by default. Close the valve, and the cabin pressure is
now isolated and available to the regs."
I'm sorry Rick, "explain it to me like I'm a two year old" Where the
cabin environment is concerned, where is the negative pressure
required to trigger the regulators on descent?
I can see Chips membrane trigger working but, this I don't get yet.
Joe
From: "Rick and Marcia" <empiricus@telus.net> Reply-To:
personal_submersibles@psubs.org To:
<personal_submersibles@psubs.org> Subject: Re:
[PSUBS-MAILIST] Ambient / 1ATM Q? Date: Fri, 20 Jan 2006 00:23:40
-0800
Hi, Patrick, Bill, et al . . .
I did not realize Rick and Joe
were using constant air flow in their ambient designs. Now I see why their
hull interiors are almost devoid of water vapour.
Regarding
constant flow: I'm not sure if Joe is
intent on using constant flow in his sub or if he was
using the term by way of explanation.
My ambient will use a bank or manifold, if you
will, of regulators. There will be no constant flow.
The regs I'm talking about are standard scuba and are sometimes referred to
as DEMAND regs (as opposed to CONSTANT FLOW). By only
demanding air when you need it you save your supply.
As Rick pointed out earlier this
can be handled by dessicant absorbant which is a powder which absorbs
water.and basically wicks water out of the air. The air in their
tanks is much dryer than normal air also so this helps too.
I've used the
term "bone-dry" in previous posts and, as Bill
has pointed out, there really is little likelihood of anything being
bone-dry in a sub cabin. I spoke in relative terms. Desert air
is considered "bone-dry" yet actually contains a significant amount of water
vapour. Just ask anyone who's had to do a miliary survival
course.
Magiacl Child's system will
be similar to using Barolyme to absorb CO2. Initially I had
intended on venting our (breath) exhalations directly from our oral/nasal
masks to the surrounding water. I've since experienced an
epiphany and am now thinking of simply exhaling straight into the
cabin. In this scenario, the dessicant would simply absorb the water
vapour from the cabin air (but wouldn't purify it). The cabin's
overpressure valve would occasionally burp the excess pressure to the
surrounding water.
The down side, of course, is that the cabin
air would be perennially stale and would support us for less time
should we need to stop using our masks. Exhaled CO2 still contains a
lot of O2 since the body doesn't metabolise all the oxygen. So, there
is still some breathing room so to speak. Mind you, that's what pony
bottles are for.
What all ambients have in common
whether they have an opening to the water (like in an upside down glass) and
use the rising water level to trip a float, valve or sensor which then activates their air tanks
to vent, or whether they are closed to the
water and use a valve or sensor, is that they use internal air pressure to
push back against the external water pressure
A
sealed cockpit obviates the need for a sensor of any kind since the
regulators themselves do the job for you (hence, the term
"regulator"). The demand regulator is a valve in itself. The
rubber diaphram in front of the mouth piece physically pushes a
lever that opens the valve.
I'd like to add to this by saying that a semi-dry ambient can also
use this system. How? Once the required amount of
ballast water is admitted, you seal off the cockpit so that the regs
take over. Open the valve, the cabin is exposed to surrounding water
and the regs are disabled by default. Close the valve, and the cabin
pressure is now isolated and available to the regs.
Confused yet?
Rick L
.
----- Original Message -----
Sent: Thursday, January 19, 2006
11:40 AM
Subject: RE: [PSUBS-MAILIST]
Ambient / 1ATM Q?
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
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