[PSUBS-MAILIST] Oil Compensator

Wed Apr 5 21:43:51 EDT 2017

Hank,
did you add a 0 by mistake?
$50,000
If that's right I better get back on to my thruster project.
Alan

Sent from my iPad

> On 6/04/2017, at 12:31 PM, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
> 
> Alan,
> I think magnetic couplers are the way to go if you have the money.  Nuytco is selling them like mad for 50,000 a pop.  That says it all to me.  The potential for muck causing a problem is non existent to me.  It is the same with a mechanical seal.  I don't think it has to be big either, when you look at the original DW magnetic coupled motors.  They are no bigger than a Min-Kota
> Hank
> 
> 
> On Wednesday, April 5, 2017 6:26 PM, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
> 
> 
> Greg,
> The big difference with oil filling is cost savings.  The power loss is no issue because we have WAY more battery power than we need as a rule.  I have never even come close to running out of battery power, and I travel miles.  When I change oil annually, the oil is defiantly darker from carbon I assume, but the motors still look great inside with no noticeable brush loss.  
> I do agree though that air would be nicer and cleaner, especially now that it is well perfected.
> Hank
> 
> 
> On Wednesday, April 5, 2017 6:08 PM, james cottrell via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
> 
> 
> Cliff/Hank,
> 
> I have to say I agree with Hank on this point. The Minn -Kota was designed to operate with a small amount of external pressure. Pressure compensation with air only needs to be sufficient so that the design limits are not exceeded. Positive pressure (such as during ascent) should be escaping through the scuba regulator.
> On the other hand, Cliff is a sharp guy so now I'm curious.
> As far as the space between the inner and outer shaft seals- I don't know if sea level pressure in that space would cause a problem or not. It's worth checking.
> 
> Also, as long as we are on the subject here are some other things-
> Brush contact pressure is sometime increased in oil filled DC motors.
> Arcing in some oils can produce carbon like deposits.
> Rotating assemblies in oil DO consume some energy,
> Friction from rotating assemblies in oil can also create additional heat (although I think it is inconsequential).
> Some sort of Bellows type device is usually added for compression/ expansion in "real" systems.
> 
> All and all, I'm liking air comp more and more for home built subs that don't have complete oil filled tubing electrical systems.
> 
> Greg C
> 
> From: hank pronk via Personal_Submersibles <personal_submersibles at psubs.org>
> To: Personal Submersibles General Discussion <personal_submersibles at psubs.org> 
> Sent: Wednesday, April 5, 2017 6:51 PM
> Subject: Re: [PSUBS-MAILIST] Oil Compensator
> 
> Cliff,
> I am confused as to why you would want a 4 psi internal pressure pushing against a spring that is trying to keep the seal tight to the shaft.  I would think the seal should be reversed with a 4 psi internal pressure to assist the spring  in keeping it tight to the shaft.  This will also apply to an oil filled motor, in the case of oil filling, the 4 psi would be beneficial in keeping the seal tight.
> Hank
> 
> 
> On Wednesday, April 5, 2017 3:50 PM, Cliff Redus via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
> 
> 
> I covered this in my Psub presentation at the 2016 PSub convention.  But will hit the highlights.
> The Minn Kota 101 lower unit (MK part number 2886289) had a shaft seal on the end of the shaft that is connected to the prop.  The seal arrangement consists of two identical lip seals oriented to see external pressure.  The inner lip seal lands on a shoulder in the Brush End Assembly.  This cast aluminum part does three things. The first is hold the DC brush assembly, the second to hold a brass or bronze journal bearing, the third is to provide a cavity to land two lip seals.  The stock MK-101 lower unit the two lip seals separated by a cardboard spacer.  This seal arrangement is design for a low differential pressure on the order of maximum 30 fsw or about 13 psig.  Antidotal experience is that this seal assembly has withstood three times this depth. 
> For the last two years I have been operating with this stock seal arrangement on the four thrusters on the R300.  I use a WATTS R364-02BSS/M1 REGULATOR part number 364-02BSS/M1 to do pneumatic pressure compensation of my four thrusters. I supply pressure to the regulator from the LP pressure side of a scuba first stage regulator and have it adjusted to supply pressure at 4 psi above ambient water pressure. The scuba first stage regulator is supplying pressure to this reducing regulator at 50 psi above ambient water pressure.  This is a relieving style pressure reducing regulator meaning that  when you ascend, pressure vents from the regulator body. The deepest I have had this arrangement is 160 ft.  To date I have had no thruster flooding but I don’t have a lot of hours on the units.
> As both Sean and Alan have pointed out this two lips-seal arrangement is correctly orient for low pressure applications like the original intent of the MK 101 units but not ideal for a pressure compensated deep diving thruster.  As Alan pointed out, the 1 atm air initially between the two lip seals is an issue as well as the cardboard spacer.  The outer lip seal will see more pressure that it was designed for which could lead to it failure with the lip rim on the ½” shaft being pushed in which could flood the 1 atm space and damage the cardboard spacer.  At this point the inter lip seal is the only seal holding and it is seeing a 4 psi differential pressure with the pressure inside actually being higher than ambient.  I have not torn down my 101s to see if the space between the lips seals was flooded. 
> I hope to do some testing of different seal arrangements for the MK 101 lower unit in my test chamber at some point. I just have not had time and since my thrusters have been behaving, not strongly motivated. 
>  
> The idea of using this pressure reducing / relieving regulator came from Hugh Fulton as he has installed the system on the Q-Sub.
>  
> Cliff
> 
> On Wed, Apr 5, 2017 at 3:29 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.
> 
> 
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