[PSUBS-MAILIST] Motor Modification

[Alan James via Personal_Submersibles]

Rick,
one method Psubbers were using to compensate thrusters was to have two nipples
in the thruster with a piece of PVC tube leaving one, wrapping around the thruster
& joining the other. The idea being that the oil filled PVC tube compressed to equalize the thruster.
It's easy to squeeze the tube with your fingers, but when you have water pressure
squeezing evenly, it's collapse pressure is quite high. Also lights are compensated like 
this with the wiring running through oil filled PVC tube from the back of the light fitting
to the through hull. Again, the tube needs to be crimped to initiate it's collapse.
   With the addition of a bladder there is no need to worry about this, as the bladder collapses 
easily. If you semi fill the bladder then it can take any expansion. As long as there is enough
oil in the bladder to cover the compression of any air at the depth you are going, then
you could have quite a bit of air still left in your thruster. But the ideal is to have
as little as possible.
   I know Cliff mentioned the problem of the dual seals when he was doing his Minn Kotta
modifications. I think he built a new end section to the motor, but aren't sure.
   I have heard that the Minn Kotta seals are rated to 15-30ft but have been tested
to over 100ft in some cases. I have only looked at them from an obscure parts diagram.
There may be such a small void between them that it would be a non issue if the seaward seal
fails. Sometimes in thrusters with dual seal arrangements the seaward seal is regarded 
as sacrificial because it sees all the grit etc.
   Today I am emailing manufacturers to try & find a cheaper version of the Parker PR364
relieving regulator that Cliff is using for compensation.
Cheers Alan
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