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 d! istresses 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