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Of course I know that water molecules do not compress. Water is basically
uncompressable, but it can be pressurized.
I should have said "pressurize" instead of "compress" when I was talking
about the pump exerting force to move the water.
It was a symantic error, but hopefully you knew what I meant, just like I
know when you wrote "nozel" and "nozels" that
you actually meant "nozzle" and "nozzles", and when you called me "Atkins"
you actually meant "Akins". I will try to
watch my terms and keep them technically correct in the future.
You explained that the pump can suck and blow just as efficiently at 1000
ft as at 10 ft. I'm still trying to wrap my head around that.
In order for there to be an area of high pressure created by the impeller
at the pumps exit nozzle, doesn't there have to be an area of lower
pressure
on the other end of the impeller? If that is true, then
wouldn't an increased depth create more ambient water pressure on the low
pressure side and
make it harder for your pump to pressurize the water and result in less
force coming out the exit nozzle, and eventually equalize the pump's entire
force
output if you went deep enough? What am I missing here? As I said
before, I really haven't given this a lot of thought and just voiced the first
questions that came to my mind.
Bill Akins.
----- Original Message -----
Sent: Saturday, April 08, 2006 1:42
PM
Subject: Re: [PSUBS-MAILIST] motor
thought
In response to Bill Atkins:
Water doesn't compress. The pump simply sucks water in and increases it's
velocity. The nozel then decreases the apeture which creates pressure as the
large volume of water increases speed to get out of the smaller opening.
Since water doesn't compress, the pump can suck and blow just as
efficiently at 1,000ft as 10ft. Certain other fluids have been created that do
not compress, but also lubricate and protect. These hydraulic fluids would be
the best thing to seal an electric motor at depth. As long as the seal
can keep the fluid in at sea-level, it should be capable of doing the
same when submerged. Then a seal much like a dripless packing tube found on
inboard-powered boats may be an adequate seal.
I would still rather have two pumps on board, in case one failed, and to
give added manueverabilty. Also I'd want to be able to aim the nozels.
My question, however, is this- would a jet stream be as efficient as a
propeller AT SLOW SPEEDS? The benefit of a propeller is that it can be tuned
to the work it is doing. Angle, pitch, diameter- a psub like ours will have a
lot of resistance and won't be very fast.
That being said, consider this: A hydraulic pump mounted inside the hull,
driven by an electric motor. This pump works on a closed-system, and
recirculates hydraulic fluid which drives propellers. Again, I'd choose two
pumps (one for each side, which provision to drive both props off just one
pump), for added safety and manueverabiltiy. You don't have to
pressure-compensate anything, and no moving parts are exiting the main hull,
just a few pipes with cut-off valves.
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