[PSUBS-MAILIST] Oil Compensator

[Cliff Redus via Personal_Submersibles]

I just got off the phone with the Parker guys, their elastomer seal group
out of Utah.  I discussed the MK-101 application issue with them as it
applies to my boat (air compensation, 4 psi differential, 450 fsw max
ambient). I guided the conversation towards the KISS principle rather than
evaluating more sophisticated seals such a double mechanical cartridge
seals. The guy I spoke with said that the 1-atm gap between the two lip
seals, as per the manufacturers original design, is very likely to cause
a problem as well as seal orientation.  His recommendation was to use the
two existing lip seals but to reverse them, so that the outer bound seal
could handle the situation where the pressure compensation is off and boat
is just sitting in the water over night and the inner seal is oriented so
it can handle the normal operating condition of a 4 psi higher internal
pressure than ambient.  He also suggested using a seawater and freshwater
resistant grease between the seals rather than oil to help prevent  this
barrier fluid from leaking out. He also suggested removing the cardboard
spacer.  Under normal operating conditions when the thruster is being
pressure compensated, the 4 psi is trying to push both seals out of
the Minn-Kota Brushed End Housing part but due to the lip seal interference
fit, they should stay in place.

I am inclined to give this a try. Not sure what greese to try but a quick
look online looks like  DuPont Marine Grease with Teflon fluropolymer might
work.
https://www.amazon.com/DuPont-Teflon-Waterproof-cartridge-DGM614101/dp/B003UTX0N2
http://www.performancelubricantsusa.com/product/marine-waterproof-grease.php

Does anyone have a better recommendation for a saltwater -freshwater
resistant grease for this application?





On Mon, Apr 10, 2017 at 9:27 AM, Jon Wallace via Personal_Submersibles <
personal_submersibles at psubs.org> wrote:

>
> What I've gleaned so far is that regardless of oil vs air method, nobody
> has addressed the space between the shaft seals on the minn-kota so from
> that perspective the methods are equal.  Regarding that void between the
> seals I have to again wonder if the two seals are really necessary in a
> compensated system.  I'm looking at one of my MK101 lower units and the
> space between seals is about 6mm.  But for sake of argument, assuming both
> seals are required, could you not simply remove the spacer and outer seal,
> fill some part of the void with oil and then discard the spacer but install
> the outer seal so it butts against the oil reservoir creating a sandwich of
> inner-seal, oil, outer-seal.
>
> I really like the air compensation system that Greg and Cliff described.
> While it is simplistic in theory, I am concerned that I am going to end up
> with an octopus of tubing trying to retrofit it to the K-600 using the
> existing hull penetrations.  However, not needing to pot the wires at the
> motor or worry about fluid creep between insulating wires is attractive.  I
> also notice in my unit that there is white grease lubricating the thrust
> bearing and shaft seals.
>
> Jon
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