Re: [PSUBS-MAILIST] Seals again

[s_lindblom@conknet.com (Steve Lindblom)]

The pressure on the hub is balanced by the pressure on the other side of
the hub. The only pressure that is exerted on the internal components via
the shaft is the pressure acting on on any area of the exposed drivetrain
WHICH IS NOT BALANCED on the other side - that is to say, the part that
goes through the seal. A smaller shaft will transmit less pressure. The hub
size has nothing to do with it.

Draw a picture and it'll make more sense. Draw a square to represent the
housing. Surround it with little arrows pointing in to represent ambient.
Lets say each arrow represents 10 lbs of pressure. Now draw a line through
one side. That represents the prop shaft. just to make it clear, make it
protrude an inch from the side of the square.

 Now draw a line across the exposed end of the shaft line. That represents
(in cross section) the hub. Continue drawing the little arrows all the way
around both the shaft and the hub. Now, if you've spaced the arrows evenly,
you will notice that no matter how big or little you make the hub, the
arrows will balance EXCEPT FOR THE ONE IN THE MIDDLE OF THE HUB opposite
the shaft.

>"The pressure on the armature/shaft at depth is going to be equal to the
>area of the shaft where it comes through the seal, times the pressure."
>
>Wrong.  It's at least going to equal the pressure exerted on the area of the
>prop hub.


>Again, you need to re-calculate the force exerted on the shaft AND
>everything attached to it: i.e., the prop.  It's a lot more than you think
>it is.
>