Re: [PSUBS-MAILIST] Seals again

[s_lindblom@conknet.com (Steve Lindblom)]

Exactly! That's the principle, among other things, in balancing a
regulator. An alternative way to do the same thing would be to extend the
prop shaft through the prop and put a little remote air chamber connected
to the main motor housing on the end, and pressure balance it that way.

However any motor built to drive a propellor has to be designed to handle
the thrust from that source, since the thrust the motor creates in
operation is transmitted from the propellor to the motor housing and boat
via the shaft. So a robust thrust bearing will be part of any direct drive
propellor motor, and is usually capable of handling a little extra load
from the water pressure without undue stress.

Also, adding balancing as you describe would require an additional set of
seals, which would double the potential failure points. However, balancing
a motor as you describe could be very useful in some high pressure
applications.

BTW, if Nemo's theory was true, that the thrust on the shaft due to water
pressure was equal to the size of the hub, then you wouldn't need power the
motor at all - just make the hub big enough and let the water pressure
drive the boat along - the deeper you went, the faster you'd go!



>That makes a lot of sense, although one thing I'd like to point out is that
>on all of the electric motors I have there is a hole on the other side of the
>motor housing with the other end of the shaft stuck into it, so if there was
>another shaft sticking out the other side of the submersible housing then
>there WOULD be a compensating arrow on the other side of the shaft.
> Now I know that something like that isn't always possible with all sub
>designs, so I guess a set of ballbearings or something