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SCUBA-L  February 2001, Week 3

SCUBA-L February 2001, Week 3

Subject:

Re: FYI - Cozumel Conditions

From:

David Strike <[log in to unmask]>

Reply-To:

Scuba diving discussion list <[log in to unmask]>

Date:

Tue, 20 Feb 2001 17:52:38 +1100

Content-Type:

text/plain

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text/plain (46 lines)

On Tuesday, February 20, 2001 5:05 PM, Tim wrote:


> since im a newbie, ive got some more questions. what the difference
between
> the 1st and 2nd stage for a regulator??

In simple terms the purpose of the regulator is to reduce the pressure of
gas contained in a cylinder down to a level comfortable enough to keep pace
with the diver's breathing requirements.  It achieves this in two stages.
The first stage reduces the pressure of the cylinder contents down to an
intermediate pressure that remains at approximately 10 bars above ambient
pressure.  This pressure is further reduced by the action of the regulator's
second stage, or demand valve, to provide easy and effortless breathing.

Although all scuba regulators follow these basic principles the method
varies according to the type of first stage used.

Without delving too deeply into the mechanics, regulators fall into one of
two broad categories, Balanced and Unbalanced, each of which has its own
distinct characteristics and sub-types.

In the Unbalanced Regulator, both cylinder pressure as well as ambient
pressure acting on the first-stage mechanism will determine the gas flow
available at the intermediate stage.  Now usually governed by a piston
assembly and employing a relatively small orifice, an unbalanced regulator
is limited in the amount of gas that it can deliver, particularly when the
cylinder pressure falls.  In the shallower diving ranges (less than
30-metres), this is seldom a hindrance but can become more problematic at
depth or in an air-sharing situation.

Usually employing either a diaphragm or a piston, a balanced regulator has a
much larger orifice and relies on mechanical forces rather than cylinder
pressure to deliver a high constant pressure of gas.   A characteristic that
makes it more suited to deeper diving and high exertion swimming.

>also, how do you calculate for the
> lift capacity for the bcv?? thanks, tim.

Because we use a metric system, I find it easier to calculate.  As a rule of
thumb,1 litre of water = 1 kg of lift.  Topping the BCD bladder up with a
measured amount of water makes it easy to calculate its potential lift
capacity.   :-)

Strike

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