Re: [PSUBS-MAILIST] pressure gage

["Jens Laland" <laland@artematrix.org>]

David

A typical pressure gauge utilizes an invention called the Bourdon tube to
translate pressure in the tube to a linear movement of a needle on a gauge
face. A Bourdon tube is typically a thin stainless steel tube with an oval
cross-section that is bent into a semi?circular or coiled shape.

The tube is sealed at one end and open to the pressure source at the
other. As the pressure increases inside the Bourdon tube, it causes the
tube to expand and straighten, thereby causing its shape to change. A
mechanism is then used to translate this increased radius to a linear
deflection of the dial.

Because the outside of a Bourdon tube is subject to ambient pressure in
the sub, this pressure becomes the reference and the measured value shows
only how much higher the water pressure (at diving depth) is in comparison
to the ambient pressure inside the sub.

So, I guess you may have a problem, unless you go for a gauge that
provides true absolute pressure readings.

Best regards,
Jens Laland

PS.: You could probably operate an ambient sub down to about 80 ft. using
a homemade, calibrated Papenberg depth gauge (which is of similar design
as the depth gauge used aboard David Bushnell's "Turtle")




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