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Rick,
I
don't think that a bilge pump has enough power to pump against the head pressure
at depth, and if they do your flow capacity would be greatly diminished. If
your regulator fails, you will not be able to pump water
out.. Also most bilge pump housings are made of plastic and
the motor housings would implode and flood under ambient pressure as you
descend. Bilge pumps are basically centrifugal pumps which are not really
suitable to operate against a lot of pressure. I personally wouldn't use
it. But again, this is each individual's choice.
One of
the important aspects in the design of a VBT system is that it should work to
1.25 times of its mawp (maximum allawable working pressure). This is not an
arbitrary number. This is designed as a safety margin and to ensure that the
variable ballast system will function in the event that you end up by accident
deeper than you intended to. Hugo
On
another note this is for the entire group in general.....
There
is a lot of material out in the reference books in the reference material
section of the PSUBS web site with lots of information on proven manned
submersible systems designs that are guaranteed to work and which
are reliable. I don't want to discourage
anyone here, however, sticking to proven designs and keeping it as simple
as possible for your application will save the prospective psub builder a lot of
grief and headaches. If the psub builder is adamant to build a submersible with
innovative designs into the submersible's systems which have never been proven
to work reliably in real world applications he should do a thorough testing of
his design under the same conditions he expect to dive.
I strongly suggest that anyone
building their own submersible thouroghly study (not just read) and at least try
to understand the reasoning behind the ABS or Lloyds guidelines for
designing and building manned submersibles. These guidelines are there for
the safety of the human lives in the submersible as the primary
concern. They were created as a result of accidents that cost the lives of
people who were smart, but who did not put safety in the first place.
NEVER ASSUME THAT EVERYTHING WILL BE OK. If a sub builder goes about
designing and diving submersibles with the mentality that "this will never
happen to me" he is putting himself (and others) in a very precarious
situation. I hate to be the one that keeps bringing this up, and I am
sorry if I am raining on someone's parade. It distresses me greatly when I feel
that safety is given a second place ahead of cost and ingenuity, and I would
hate to see any Psubber involved in a fatal accident.
Like
Forest Gump would say... "That's all I have to say about
that"
regards,
Hugo
-----Original Message-----
From: Rick and Marcia [mailto:empiricus@telus.net] Sent: Wednesday, January 04, 2006 1:41 PM To: personal_submersibles@psubs.org Subject: Re: [PSUBS-MAILIST] Compressable ballast tanks 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 venti
Your hissing overpressure valve serves the
same function as the regulator's exhaust ports.
Your thoughts?
Rick L
Vancouver
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