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Shallow Water Seal?

  1. Feb 19, 2009 #1
    I asked another question in a previous thread, but this is a new issue so here's a new thread:

    Basically I need to design some kind of waterproof shaft seal for the use of an underwater ROV. Following some earlier advice, I looked into the Parker O-ring Handbook and found the easiest way is just to have o-rings complete the seal, recessed into grooves.

    The operating depth I expect to be working in will be no more than 4 meters, so it will be fairly shallow... will this simple o-ring seal be enough to keep water out? And if so, any advice as to how I should go about machining this seal?

    It is going to be for a stepper motor that will let my thruster assembly rotate.

    Thanks!
     
  2. jcsd
  3. Feb 19, 2009 #2

    mgb_phys

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    How fast is it going to rotate?
    If you just want a seal for the pitch bearing of a moveable thruster then an o'ring set would be fine (slow occasional movement)
    If you want to seal the drive shaft of a prop ( continual fast movement) then it's trickier.

    You want to use a number of O ring (3-4?) in a row. Probably easiest to turn the grooves in the shaft, you will also want some sort of collar to hold the shaft in place.
     
  4. Feb 19, 2009 #3
    yea, its going to be slow occasional movement... a stepper or servo motor that adjusts the angle of the thruster from like 90 degrees, 45 degrees, etc... its not going to be as fast as like the thruster itself, and its not going to be constantly in motion

    how would i turn a groove on the inside of a shaft thing though? the manual had pictures that implied cutting a groove on the inside, while the shaft itself was intact. but i guess it would be easier to cut a groove on the shaft itself...
     
  5. Feb 19, 2009 #4

    mgb_phys

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    Most boat prop shaft seals put the seals in a replaceable housing around the shaft.
    This keeps the prop shaft intact and stronger but in your case it's probably easier to have the o ring grooves on the part that turns because it will be easier to machine and assemble.

    I assume you are going to want a hollow shaft because you need to get power out to the thruster motor so you migth as well do all the tricky maching on this part.
     
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