The advantage of an oil bladder over an air bladder is that it isn't
compressible and thus wont change volume as depth increases. No
volume
change means no change in buoyancy.
What you're basically doing with the oil bladder system is changing
the
amount of air volume _inside_ the sub. The weight of the sub and the
oil is constant, so if you increase the volume of the combined system
you increase it's buoyancy.
The problem with an air bladder (such as a BCD) is that as depth
changes the buoyancy changes in a way that causes the depth to change
more (a feedback loop).
In SCUBA there isn't another convenient way to do it (and the diver
has
a lot of compressible flotation anyway). The SCUBA diver also has a
second variable air bladder they can use for quick small adjustments
(their lungs).
In a submarine you don't have that so it's critical to keep your
compressible flotation to a minimum. There is also the issue of task
loading on the operator, though a person could probably manage a
spongy
variable ballast system it would be a really bad idea given the number
of other things the pilot should be monitoring.
This would be applicable to both ambient and 1 atm subs since both
displace a constant volume of water regardless of depth.
mike
On Aug 11, 2004, at 8:44 PM, david cutajar wrote:
I would think that the simplist system would mimick
the BCD we use when we SCUBA. Exactly as Dave stated,
just an external Bladder; but why not just use Air -
is it too compressible and must be adjusted more often
than oil? i.e. compresses too much as you descend???
I wonder what the advantage of oil in this situation?
Is it the ability to pump it back in and it doesn't
use up all that air???
For air, just have a momentary valve for input (into
the blader) and one for output (exhaust out of the
bladder)and make small adjustments to your bouancy as
required.
just some thoughts---$.02
David Cutajar
--- Mark <gadgetsboy@ntlworld.com> wrote:
I'd be interested in a look myself
Mark
----- Original Message -----
From: JANE PATTON
To: personal_submersibles@psubs.org
Sent: Wednesday, August 11, 2004 5:50 PM
Subject: Re: [PSUBS-MAILIST] Found this article
and thought it may be ofinterest
Hi Dave
Where could I find a sketch of the oil bladder
system you speak of?
Rick
----- Original Message -----
From: Fly Deep
To: personal_submersibles@psubs.org
Sent: Wednesday, August 11, 2004 5:24 AM
Subject: Re: [PSUBS-MAILIST] Found this article
and thought it may be ofinterest
Mark, the easiest and simplest VB system I've
ran across so far is one smiler to what is used on
the Deep Workers. Its a simple oil tank on the
inside and a small hand pump like a jack that can
push the oil to the outside of the pressure vessel.
As the bellows increases in size out side the
pressure vessel it displaces water and there by
adjusting the Buoyancy....Dave
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