[PSUBS-MAILIST] Motor Modification

[Sean T. Stevenson via Personal_Submersibles]

Do the Minn Kota motors have a dual seal arrangement that would permit you to run a compensation line to the void between the two seals?  I am not familiar with their design. In designing mission critical sealing arrangements, I have always stuck to the rule of thumb of using any single seal to change fluid, or to change pressure, but not both simultaneously.  Thus an ideal arrangement with dual seals would be to run bias compensated oil in the housing, unbiased compensated oil in the volume between the seals, and then the seawater outside. This way, leakage across the inner seal is immaterial because the fluid is the same, and leakage across the outer seal is unlikely because there is no delta-P.

Sean


On December 5, 2016 3:58:49 PM MST, Alan James via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>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
>
>
>------------------------------------------------------------------------
>
>_______________________________________________
>Personal_Submersibles mailing list
>Personal_Submersibles at psubs.org
>http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.whoweb.com/pipermail/personal_submersibles/attachments/20161205/f57a5b79/attachment.html>