[PSUBS-MAILIST] Motor Modification

Tue Dec 6 08:11:26 EST 2016

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 modified
>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 for 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 could 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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