[PSUBS-MAILIST] Thruster Reliability

Tue Jul 25 21:03:43 EDT 2023

River,Sounds like you are gaining a lot of experience in that job.Can you tell me what viscosity silicone oil you use, thanks.I printed & bound the first of those documents you refered to a few years back. There was also "Rotary shaft seal selection handbook for pressure-equalised deep ocean equipment."One thing I gleaned from that reading is that there is always an internal over-pressure of around 5psi used. That is why I am working on an over-pressure regulator.Alan

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  On Wed, 26 Jul 2023 at 12:08 pm, River Dolfi via Personal_Submersibles<personal_submersibles at psubs.org> wrote:   Cliff,Those sound like signs of an incompatible fluid to me. Especially considering the length of time that the thrusters were filled with WD40 compared to the hours they have run in the field.
The US Navy created a bunch of technical reports on various aspects of deep submergence systems design, and distributed them among defense companies and researchers as part of the "Deep Submergence Systems Project" in the 60's and 70's. All of the documents are now approved for public release and readily available online. This one is particularly interesting and relevant to this conversation. I consult it often enough that I have a physical hard-copy on my office shelf."Handbook of Fluid-Filled, Depth/Pressure-Compensating Systems for Deep Ocean Applications"https://apps.dtic.mil/sti/citations/AD0894795There is also:Handbook of Fluids and Lubricants for Deep Ocean Applications
https://apps.dtic.mil/sti/citations/AD0866350

I suspect that the bushing wear is caused by the low viscosity of the WD40 making it a poor choice for lubrication. I've always been told WD40 is a penetrating oil, not a lubricating oil.
I maintain and operate a small fleet of ROV's and AUV's that routinely work at a depth of 6000m. All of them use motors that are compensated with either univolt transformer oil where high voltages are involved, or a silicone oil. The caveat being that all of these are brushless electric motors, so don't have the complications of carbon fouling of the fluid. 
We have been evaluating fluids that can serve as both a hydraulic system oil and an electrical system compensation oil, as we currently run two separate oils for each function. The problems we are running into are material compatibility with existing components. Things like wiring, heat shrink, seals, adhesives, etc. We know what not to do with Silicone and Univis, but the only way to determine the compatibility of a particular oil with a particular off the shelf or proprietary component, like a Minn Kota or any other motor, is testing.
Thanks,
-River J. Dolfi
412-997-2526rdolfi7 at gmail.com_______________________________________________
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