Re: 300 bar ??

[protek@shreve.net]

    Check valves in the hull require a certain forward pressure to actuate.
 The problem here is that this pressure added to the pressure differential
through the valve with air flowing may be several PSI.  Multiply this
pressure by the hatch area and it can lift the hatch anyway.  Like I said,
high pressure power piping inside the hull has risks.  I have valves for
quick shut off.  But there are still risks.  Another approach is a hatch
mechanism that can burp the air.  In other words, if the hatch given inside
pressure, opens slightly against the seal to release the pressure this can
be a check valve in itself.  Problem here is if the hatch seal is not
forced down against the seat you may have leaking till you are 5 or 10 feet
deep.  I have a hatch system that will allow this but I usually tighten the
hatch to the tight position.

Gary Boucher


At 09:24 PM 10/26/98 -0800, you wrote:
>How about a "check valve" that would blow off any pressure reached over
ambient ?
>If  something did go wrong and pressure did bleed out into your pressure
hull, the
>pressure would reach ambient then excess would blow out your sub via the
valve...
>Granted, if it was a large volume at once It could be slightly damaging to
one's
>ears, but at lease it would not blow your hatch off !!!
>
>A. Long
>
>protek@shreve.net wrote:
>
>> 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)
>> >
>> >
>
>
>
>