[PSUBS-MAILIST] Oil Compensator

Wed Apr 5 16:43:13 EDT 2017

Jon,I agree with Sean, orient the seal inward to keep oil in and the outer seal outward to keep water out.  having said that I also agree with you that a single seal oriented to keep oil in will work.  I will do both when I take Gamma out for a trial  run before the pressure test.  I will set up the  two travel thrusters for the experiment.  I have them set up the way Sean suggests at the moment.  A submersible pump has one seal oriented to keep oil in with a rubber spring loaded  bladder for compensation.  Just for interest sake, I have two MinKota thrusters for vertical thrust with the motors mounted with the props at the top.  I have NO compensation system and no leaks that are noticeable, and when I change the oil (WD40) annually, I don't see water.  I am sure there is some and I am sure they leak some oil, but never have I seen evidence on the surface.Hank 

    On Wednesday, April 5, 2017 2:30 PM, Jon Wallace via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

  Hi Alan,

 Yeah, that white paper pretty much just states fill it with oil and you're good to go.  It doesn't address some of the issues that have come up on the list regarding heat and expansion, inter-seal cavity, etc.  I understand the drive to find a perfect solution and that minn-kota oil compensation is not perfect, I'm just trying to understand the real-world ramifications of using it as that white paper suggests and most psubbers have implemented.  Given that water is such a good heat sink, are the heat and expansion issues of the oil really that serious?  I know Alec wrote something about his experience with this some time ago but am having a hard time finding that thread.  Pretty sure SNOOPY is still using simple oil compensation regardless.

 Jon

 On 4/5/2017 4:02 PM, Alan James via Personal_Submersibles wrote:

   Jon, Cliff has been doing a lot of work on Minn kota modifications & has the hands on experience. If he's not tuning in it would be worth contacting him privately. The Minn-kota seal set up is not ideal, with the gap between the two seals meaning one or the other seals will fail when their pressure rating is exceeded. The outer seal seems to serve a double purpose, being the first line of defense against water ingress & also a sacrificial seal that will see all the abrasive muck stirred up by the prop. Noticed in this kit that the outer seal has a shield to protect it.  Historically in deep diving set ups they have had dual seals, but with either ambient pressure between them, or a cascaded pressure system, and normally mechanical seals. The outer seal was regarded as sacrificial.    Maybe you could pack between the seals with grease to reduce the air gap.  I am not sure whether you could simply reverse the inner seal or not as they need a shoulder that the pressure will push them up against. Cliff is using a small relieving air regulator to compensate his motors. The regulator is fed air from your tanks & is set at an overpressure of about 4psi. The regulator is orientated upside down as the relieving air feeds out through the handle portion & the orientation will stop water entering when this valve opens. This system was suggested by Hugh, & Cliff is trialing it. It has the advantage that you could either air or oil compensate. If your motor ran out of oil it would just be replaced with air above ambient pressure. I am not sure at what pressure the relieving valve opens.    There is this very good Psub resource from an expert in modifying Minn kotas for underwater use.  

 _______________________________________________
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/20170405/25d5e4d7/attachment.html>