[PSUBS-MAILIST] Lip Seals - Thruster Pressure compensation

Sat Feb 21 19:27:41 EST 2015

Cliff,using the regulator for pressurizing your thrusters, you will be able to haveboth air & oil systems by just adding or draining the oil. It will be easy for you to have both operating concurrently for a comparison.I would be interested in heating comparisons between oil & air if youhappen to do them.Alan
      From: Cliff Redus via Personal_Submersibles <personal_submersibles at psubs.org>
 To: Personal Submersibles General Discussion <personal_submersibles at psubs.org> 
 Sent: Sunday, February 22, 2015 4:31 AM
 Subject: Re: [PSUBS-MAILIST] Lip Seals - Thruster Pressure compensation

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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