[PSUBS-MAILIST] Lip Seals - Thruster Pressure compensation

Sat Feb 21 10:52:41 EST 2015

Cliff,
The oil leak issue is on my main drive, not on a thruster.  Funny though, my vertical thruster is an old 50 lb Minn Kota and has no compensation system at all.  I just filled it with WD and left it alone.  The motor is oriented  vertical with the prop at the top and gives me no trouble at all.  The shaft seal that is leaking a tiny bit is a simple low pressure seal with the lip inside and a small lip outside.  The stiffer ball compensator seems to have helped a lot.  I think at this point I will change to a higher pressure seal.  
Gamma also has a second drive shaft that is coupled to the main shaft for jettisoning.  The second shaft is in an oil filled housing with the same simple seals and no compensation method at all.  I use vegetable oil for environmental reasons so I am not to worried about a drop of oil escaping.
Hank    --------------------------------------------
On Sat, 2/21/15, Cliff Redus via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

 Subject: Re: [PSUBS-MAILIST] Lip Seals - Thruster Pressure compensation
 To: "Personal Submersibles General Discussion" <personal_submersibles at psubs.org>
 Received: Saturday, February 21, 2015, 10:31 AM

 Hank,
 thanks for posting your experience with this oil leak and
 your steps to mitigate.  I am interested in this thread as
 I am in the process of installing four MK-101 as thrusters
 for the R300.  I have been going back and forth on air vs.
 oil pressure compensation.   My current preference is
 oil.   It seems to me that the pressure compensation
 method you choose impacts the orientation you should choose
 for the lip seals.  For those of you that have not torn
 down a MK-101 lower unit, they have a two lip seals on the
 prop shaft. These seals are oriented such that as the
 housing is taken deeper, the outboard pressure increases
 due to ambient water pressure and causes the outer most seal
 to tighten
  down on the shaft.  These off the shelf seals can be
 reversed.  Factory assembly has both with cups facing
 outward.  These can be reversed and if you want to, you
 could even mix orientation of the seals.  If you choose air
 compensation, and plan to keep the regulated air pressure
 1-2 psi above ambient, then it makes sense to reverse these
 lip seals as the pressure inside the housing is greater than
 the pressure outboard.  On the other hand, if you use oil
 for a pressure compensation, then it makes sense to leave
 the lip seals as originally oriented.  To me, if the lip
 seals have cups facings outboard, then a soft flexible
 external bladder for the oil makes sense so that as the
 lower unit heats up and oil wants to escape, it easily
 pushes into the bladder rather than out past the lip
 seals.  If you had a stiff bladder, then oil would take
 the path of least resistance and escape past the lip seals
 as they
  are not design to see much reverse pressure. 

 Hank, I might have
 missed it in one of your post but how are the lip seals
 oriented in your thrusters and are they MK-101's?  By
 the description from your post, it sounds like yours are
 oriented cups facing inward to benefit from a stiffer
 bladder.
 For those of you that
 have MK lower units, can you comments on lip seal
 orientation and any issues with seal leaks stiff vs. soft
 bladders, and small vs large bladders?  Did you stay
 with the factory orientation of the seals (cups facing
 outward) or did you reverse them?  Any experience with oil
 leaks past theses seals? 
 BTW, 
 I  have a machine shop working on an anodized T6-6061
 aluminum replacement part for the MK101 part that has the
 external fin and the shaft  seal cavity. The modification
 I have made is to add material to the inside if this part so
 that three internal bosses are formed that have female
 threads.  Into these three holes will be threaded 316 SS
 support rods to hold the Nylon Kort nozzle.  Originally I
 was using a weldment consisting of a strap with the three
 supports to hold the Kort nozzle but  I was having trouble
 fabricating these accurately enough. I will post a picture
 of finished thruster with Kort nozzle when I get the parts
 back.
 Cliff
         From: Alan James via
 Personal_Submersibles
 <personal_submersibles at psubs.org>

 To: Personal
 Submersibles General Discussion
 <personal_submersibles at psubs.org> 

 Sent: Friday,
 February 20, 2015 8:29 PM
  Subject: Re:
 [PSUBS-MAILIST] calculation

 That's easy, you shift
 houses don't you.Interesting about the compensation & the
 lip seal needing pressure.Alan

    From: hank pronk via
 Personal_Submersibles
 <personal_submersibles at psubs.org>

 To: Personal
 Submersibles General Discussion
 <personal_submersibles at psubs.org> 

 Sent:
 Saturday, February 21, 2015 8:46 AM

 Subject: Re:
 [PSUBS-MAILIST] calculation

 Alan,
 I would
 have to stand my sub up on the nose to do that :-)
 Hank--------------------------------------------
 On Fri, 2/20/15, Alan James via
 Personal_Submersibles <personal_submersibles at psubs.org>
 wrote:

  Subject: Re:
 [PSUBS-MAILIST] calculation
  To:
 "Personal Submersibles General Discussion" <personal_submersibles at psubs.org>
  Received: Friday, February 20, 2015, 2:04
 PM

  Hank,if you
  have the dish there,
  you can pour water in to
  it&
  measure how much water, to get the internal
  volume.But
  you probably knew
 that already.Alan

   From: hank pronk via

 Personal_Submersibles
  <personal_submersibles at psubs.org>

  To:
  personal_submersibles at psubs.org

   Sent: Saturday,

 February 21, 2015 5:50 AM
   Subject:
  [PSUBS-MAILIST] calculation

  Can someone calculate
 the volume of a dish for
  me please.  The
 dish is 34in dia and 5 in deep.
  Thank you

  Hank

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