[PSUBS-MAILIST] Motor Modification

Tue Dec 6 02:02:26 EST 2016

Cliff,
thanks for wading in.
Can you fit a mechanical seal in the Minn kotta end housing?
   I have ended up choosing a mechanical seal for my brushless thruster.  (V3 0100.20.N.C.)
I firstly consulted with an N.Z. rep who recommended this bellows type seal; then after
buying it, ended up sending my drawings & description of operation to Vulcan the manufacturer, 
who independently recommended the same seal.
   I have a gap between my bearing & seal that doesn't allow for free flow of oil
& are going to drill a hole at an angle in to this cavity from the middle section
of my thruster housing.
   Glad to hear there was air coming out of the relieving valve on the regulator;
it must work! I am finalizing a purchase of some similar regulators for my thrusters.
Alan

      From: Cliff Redus via Personal_Submersibles <personal_submersibles at psubs.org>
 To: Personal Submersibles General Discussion <personal_submersibles at psubs.org> 
 Sent: Tuesday, December 6, 2016 5:06 PM
 Subject: Re: [PSUBS-MAILIST] Motor Modification

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 fromthe 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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