[PSUBS-MAILIST] Motor Modification

Tue Dec 6 09:23:56 EST 2016

Thanks Sean.  The dual lip seals on the MK-101s are spring energized to
handle this zero differential pressure issue.

Cliff

On Tue, Dec 6, 2016 at 7:11 AM, Sean T. Stevenson via Personal_Submersibles
<personal_submersibles at psubs.org> wrote:

> One caveat to the embodiment that I described:  As seals are generally
> energized by pressure, when you employ a seal to separate two fluids at the
> same pressure, you must pay attention to the seal contact in the absence of
> that pressure differential - possibly opting for a spring energised seal if
> there otherwise isn't sufficient force on the seal lip.
>
> Sean
>
>
> On December 5, 2016 9:06:33 PM MST, Cliff Redus via Personal_Submersibles <
> personal_submersibles at psubs.org> wrote:
>>
>> I can give you my experience with the seals on the Minn-Kota 101 I have
>> on the R300.  Much of this was covered in my Psub presenation at Watkins
>> Glenn earlier this year.
>>
>> The OTS Minn-Kota lower unit (MK part number 2886289) consist of a center
>> section that contains the permanent stator magnets, the plain end housing
>> assembly (bow) that contains two radial roller bearing that support the
>> shaft and armature assembly, a brush end assembly that holds the brushes, a
>> bronze flange bearing and two lip seals with a carboard spacer between them
>> each oriented to expect higher external pressure than internal.  There is a
>> static o-ring seal between the center magnet section and the plain end
>> housing assembly.  On the brush end assembly, the dual lip seals are design
>> for approximately 10 feet submergence but have been known to work to a
>> depth of about 30 ft.  To modify this MK-101 for the four thrusters on my
>> boat, I reverse engineered! the brush end assembly so that I could machine
>> a replacement  brush end assembly that beefed up the part so that I could
>> screw three 316-SS supports to hold a nylon MARLIN Wageningen nozzle 37.
>> This modify part was made of 6061-T6 and hard anodized.  This new part uses
>> the same two lip seals in the original part design and the same static
>> o-ring seal beween the brush end addemlby and the center section.  In the
>> nozzle that is welded to the center section that the two 10AWG conductions
>> exit from , I inserted a 316-SS adapter that would accept a Subconn BHB2M
>> bulkhead connector and a Swagelok 1/4" NPT to 1/4" tube fitting.  I use a
>> single pressure reducing/ releaving regulator that Hugh Fulton specified
>> for his Q-Sub for air pressure compensation of all four thrusters.  The
>> regultor is adjustable and I have mine set to hold a pressure of 4 psi over
>> ambient water pressure.
>>
>> For both the original MK-101 brush end assembly and my modifi! ed
>> version, there is no barrier fluid other than air beween the two lip seals
>> and their is no compensation line.  As Alan mensioned in an earier post, it
>> is likely that this arrangement would cause the the outer lip seal to
>> collapse againsit the cardboard spacer beween the two lip seals because the
>> initial pressure beween the two seal is initially 1 atm.
>>
>> On Jan 24th this year I took my boat to Lake Amistad and did a manned
>> dive to 155 ft. I had no issues with the thrusters either before or after
>> the deep dive. They worked great. When I was ascending from the deep dive I
>> did note that the pressure regulator was releasing air from the thrusters.
>> When I disassembled the thrusters after the dive, they were all dry.
>>
>> As to Sean's idea of using a positive bias pressure inside the thruster
>> and filling the space beween the two seals with oil that has ambient
>> pressure via a compensation line, I think this could be done fo! r both the
>> original MK-101 brush end assembly and my modified version.  Might be
>> tricky to machine the hole beween the two lip seals but I think it might be
>> possible.  Not sure how you would keep the oil place as there is no room
>> for a bladder. Might be able to use some kind of plug that would transmit
>> ambient water pressure to area between the seals.
>>
>> Before I take my boat out again, I am going to call the  *Parker
>> Hannifin* guys and get their take how to modify this seal
>> arrangement. In the spirit of KISS,  I am leaning towards just removing the
>> outbound lip seal and relying on the pressure compensation system and a
>> single lip seal. We don't put a lot of hours on this seal so duty cycle is
>> light.  A single lip seal with pressure compensation might be all that is
>> required.
>>
>> Maybe we c! ould get Jon to post the PP file on the MK 101 thruster
>> project to the PSubs web site.
>>
>> Cliff
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>   Late year I reverse enginnered
>>
>> On Mon, Dec 5, 2016 at 8:01 PM, Sean T. Stevenson via
>> Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>>
>>> Do the Minn Kota motors have a dual seal arrangement that would permit
>>> you to run a compensation line to the void between the two seals? ! I am
>>> not familiar with their design. In designing mission critical sealing
>>> arrangements, I have always stuck to the rule of thumb of using any single
>>> seal to change fluid, or to change pressure, but not both simultaneously.
>>> Thus an ideal arrangement with dual seals would be to run bias compensated
>>> oil in the housing, unbiased compensated oil in the volume between the
>>> seals, and then the seawater outside. This way, leakage across the inner
>>> seal is immaterial because the fluid is the same, and leakage across the
>>> outer seal is unlikely because there is no delta-P.
>>>
>>> Sean
>>>
>>>
>>> On December 5, 2016 3:58:49 PM MST, Alan James via Personal_Submersibles
>>> <personal_submersibles at psubs.org> wrote:
>>>>
>>>> Rick,
>>>> one method Psubbers were using to compensate thrusters was to have two
>>>> nipples
>>>> in the thruster with a piece of PVC tube leaving one, wrapping around
>>>> the thruster
>>>> & joining the other. The idea being that the oil filled PVC tube
>>>> compressed to equalize the thruster.
>>>> It's easy to squeeze the tube with your fingers, but when you have
>>>> water pressure
>>>> squeezing evenly, it's collapse pressure! is quite high. Also lights
>>>> are compensated like
>>>> this with the wiring running through oil filled PVC tu! be from the
>>>> back of the light fitting
>>>> to the through hull. Again, the tube needs to be crimped to initiate
>>>> it's collapse.
>>>>    With the addition of a bladder there is no need to worry about this,
>>>> as the bladder collapses
>>>> easily. If you semi fill the bladder then it can take any expansion. As
>>>> long as there is enough
>>>> oil in the bladder to cover the compression of any air at the depth you
>>>> are going, then
>>>> you could have quite a bit of air still left in your thruster. But the
>>>> ideal is to have
>>>> as little as possible.
>>>>    I know Cliff mentioned the problem of the dual seals when he was
>>>> doing his Minn Kotta
>>>> modifications. I think he built a new end section to the motor, but
>>>> aren't sure.
>>>>    I have heard that the Minn Kotta seals are rated to 15-30ft but have
>>>> been tested
>>>> to over 100ft in some cases. I have only looked at them from an obscure
>>>> parts diagram.
>>>> There may be such a small void between them that it would be a non
>>>> issue if the seaward seal
>>>> fails. Sometimes in thrusters with dual seal arrangements the seaward
>>>> seal is regarded
>>>> as sacrificial because it sees all the grit! etc.
>>>>    Today I am emailing manufacturers to try & find a cheaper version of
>>>> the Parker PR364
>>>> relieving regulator that Cliff is using for compensation.
>>>> Cheers Alan
>>>>
>>>> ------------------------------
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>>>>
>>>>
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