[PSUBS-MAILIST] Oil Compensator

[Jon Wallace via Personal_Submersibles]

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.

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.whoweb.com/pipermail/personal_submersibles/attachments/20170405/044fb734/attachment.html>