[PSUBS-MAILIST] Motor Modification

Tue Dec 6 10:27:05 EST 2016

You would also ideally reverse the inner seal to preferentially resist the bias pressure inside the housing (even though it may easily seal against 4 psi in the normal orientation), and leave the outer seal orientation alone to preferentially resist seawater incursion.

Sean

On December 6, 2016 7:23:56 AM MST, Cliff Redus via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>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
>>>>>
>>>>> ------------------------------
>>>>>
>>>>> Personal_Submersibles mailing list
>>>>> Personal_Submersibles at psubs.org
>>>>> http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles
>>>>>
>>>>>
>>>> ____________________________________________! ___
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>>>>
>>>>
>>> ------------------------------
>>>
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>>>
>>>
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>>
>
>
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