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Re: [PSUBS-MAILIST] motor thought
Nitpick: Nozzles increase fluid velocity, but decrease pressure (i.e.
from pump pressure to ambient). Conversely, diffusers increase pressure
at the expense of velocity.
-Sean
RiskEverything21@aol.com wrote:
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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