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Re: [PSUBS-MAILIST] Simplist VB System

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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