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Hi, Bill, Hugo -
I'm considering using a hybrid ambient VBT using a
bilge pump to empty out the VBT with a second stage reg venting into the tank to
compensate. If I'm heavy, just push the VBT bilge pump (momentary action)
switch and the tank ejects water while the reg compensates. Very
simple at scuba depths. If I'm light, just flip the switch (reverse
the polarity) the other way and the bilge pump runs water back into the
VBT. The tank's air is vented out the exhaust ports of the
reg.
Hugo, I've considered your boat's system. It
probably works better at depth to have a hard tank that you manually
compensate but I have to wonder if my idea would actually work at the
depths you go to. Hmmmm. Pump out the water, let the reg
compensate. Start surfacing, let the reg do the venting.
Your hissing overpressure valve serves the
same function as the regulator's exhaust ports.
Your thoughts?
Rick L
Vancouver
----- Original Message -----
Sent: Tuesday, January 03, 2006 10:56
AM
Subject: RE: [PSUBS-MAILIST] Compressable
ballast tanks
In
our system the regulator keeps the vbt pretty much qt 15 psi above ambient. As
you descend it automatically. On ascent we use the buoyancy of the VBT to
begin the ascent. During that time we apen the vbt vent valve to release
the pressure from the tank as you ascend. If you forget to do this, you will
be reminded by the hissing noise of the pressure relief valve.At about 600 ft
we open both flood and vent valves to use the vbt as a brake, in order to
maintain control of ascending rate.
Hugo
That's interesting, keeping the VBT close to ambient. The VBT principle
I'm familiar with isolates the tank, so it is possible to end up with
quite a large pressure differential and I've had email exchanges along the
lines of whether it is best to pressurize with air prior to opening the flood
valve at depth. Can you elaborate on this setup Hugo?
thanks,
Alec
The JSL submersibles use only HP air to adjust the
Variable Ballast Tanks, it also has an externally maounted regulator, which
keeps the pressure inside the tank close to the ambient pressure. The system
is bulletproof and in almost 10 years of working with it I have yet to see
it fail.
Hugo
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