Re: 300 bar ??

[protek@shreve.net]

Bjoern,
    Seems that I have been putting out a lot of "air" lately so why stop
now.  Most small sub designers would rather put high pressure tanks outside
the hull where any malfunction would just release air into the water and
not the inside of the hull.  I chose to place two scuba tanks inside with
me with scuba first stage regulators.  These regulators greatly reduce the
pressure.  Where I sit I can reach both main valves on these tanks as they
are in front on either side.  These regulators do not often fail with the
release of high pressure air into the system but they could.  At least I
can reach the tanks.  Once I connected the system air connection
accidentally to the high pressure side of a regulator during development of
my boat.  It blew a 300PSI flexable line like it was a balloon poping.  I
was in the sub.  Could not hear to good for a while!  If you direct high
pressure air directly into a ballast tank full of water there is no
compression of the water so the tank pressure can spike to the level of the
supply.  I have considered a restriction at the tank itself to prevent
surges with full tanks.  My tanks are around 1/4 inch thick.  There are
easy ways to test the ballast tank pressure surges without installing
ballast tank pressure monitoring thru-hull.
    In short, this is what I did.  There are risks due to high pressure air
inside the sub that should not be underestimated.  Far better and safer to
place high pressure air outside.  One other factor; all scuba tanks have
rupture disks that are designed to give way to protect the tank from
exploding if overheated when the pressure rises.  This is a violent release
of air!  If this ever happened inside the sub the occupant would probably
not make it.  I do not fill my tanks to the max allowable.  Also the inside
of a sub can reach high temps when transporting it.  They could explode the
sub itself with the hatch bolted or at least blow the hatch open.  Lots of
things to consider here.  Small leaks in high or low pressure air can cause
the inside air pressure to increase to the point the hatch blows open.
Richard Hess told of a case where the sub sunk due to blowing the hatch
open.  You can not detect slow changes in air pressure.  Need a barometer!

Gary Boucher


At 12:08 PM 10/26/98 +-100, you wrote:
>Can somebody tell me something about
>working-air-pressure inside my 1 atmosphere psub.
>I want to reduce the 300 bar from four tanks with some scuba
1.stage-regulators connected to a tank that holds the working air.
>
>Or do I have to use 300 bar directly, whit tubes and valves that handles
the pressure ? What about the risk of exploading the outside tanks when
ballast blowing, or what about high-pressure tube-exploading inside the hull ?
>
>Regards,
>Bjoern Engh (Norway)
>
>