[PSUBS-MAILIST] MK 2 Brushless Thruster

[Alan James via Personal_Submersibles]

Hank,thanks for the advice.I thought that welding would be quicker & cheaper rather than cutting  an o-ring groove& drilling & taping & recessing for 6 bolt holes. Also  a more smoother hydrodynamicfinish. I will be welding on the fins for the kort nozzle attachment so can do it all inone shot.    I will probably add a fill port in to the top of the seal compartment to aid airremoval. Once there is oil in there the only way you would get air in would berunning it out of water with some sort of reverse pumping action caused by the seal.   The double seal arrangement I am copying  from that military document onsealing & compensation. However they use face seals. This thruster is so smallthat 2 face seals would take up too much space, so have doubled up on 2 lowpressure lip seals. In the pdf it makes a good case for the secondary seal & Iintend to do most of my diving in seawater where it is a more destructive environment.All the Minnkotas I have seen have 2 seals, I think just lip seals.Cheers Alan


      From: hank pronk via Personal_Submersibles <personal_submersibles at psubs.org>
 To: Personal Submersibles General Discussion <personal_submersibles at psubs.org> 
 Sent: Friday, March 25, 2016 1:31 AM
 Subject: Re: [PSUBS-MAILIST] MK 2 Brushless Thruster
   
Hi Alan,It wouldn't hurt to clamp the end cap tight but you do have a nice shoulder for the end cap to sit on.  Any time I make a part that can and usually does warp, I make it oversize and machine it true after welding.  I am curious why you want to weld it-that big shoulder has room for an o-ring.   I would also ditch the second seal-it is an air trap.    Great project!Hank 

    On Thursday, March 24, 2016 12:27 AM, Alan James via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
 

  This is my latest brushless thruster design for scrutiny.The last thruster I made was 2 piece with one seal.I machined the last version out of aluminum rod, which was expensive & difficult.The end pieces in this design are from solid rod but the mid section is from a stock tubethat I intend to have welded to the propeller end. The back end is bolted on.Am I likely to get distortion when welding the two sections together? There is a sleevepress fitting to help give it some rigidity for welding. Should I make a jig to clamp it infor welding?The thruster is for 500ft depth & is oil filled with a slight over pressure above ambient. Oil filled mainly for cooling purposes, but also as a secondary defense against any leaks,& for lubrication of bearings & seals. I am using low pressure lip seals & have a double seal redundant arrangement. The outboard seal is orientated to keep the oil in & with theinternal overpressure should keep the water out. The outboard seal should fail first as it is exposed to abrasives, especially in sea water. The inboard seal is oriented so that it keepsany water out that may get past the outboard seal. The tube coming out of the seal cavity is for pressurizing it & for collecting any water thatmay get through & come out of suspension. I am thinking of putting a water sensor in there.Any comments welcome.Alanp.s. if image isn't big enough keep hitting ctrl & + TO ENLARGE.


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