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[Martin (Admin)]

I think this is where this should go.... via email to Mayhem.....

Hello Martin,
 
I wonder if you could help me find a piece of kit which I'm sure must be out there but which I don't even know the name of. 
 
I am trying to build something (I must be honest it isn't a boat) and it requires me to find a rotating shaft with a watertight seal so that it can be placed in a partition which has water on one side and air on the other. Making one myself is not an option because it strikes me as a tricky thing to make and I am sure I do not have the engineering skill.
 
I have been trying to think of applications of such a thing so that I might see if they fit my purpose and the only thing I have come up with is submarine propeller shafts.  I reasoned that the submarine interior would be full of air and obviously the submarine would be designed to be underwater.  I am aware however that it might not be as simple as that.
 
Quite obviously I'm lost and was wondering if you might be able to let me know what kind of products there are out there and possibly point me in the right direction.
 
Many thanks,
 
Ralph

[Sub driver]

contact Pandan model boats and speak to Dave, he sells subteck seals designed for submarine prop shafts,

www.pandanmodelboats.co.uk 

[carstairs]

Thanks Sub driver.  I'll give Dave a call and see if he can help.

[Mike_K]

Is there anything that will seal a threaded shaft in rotation?  I have an idea to have the piston in a pistontank move along the threaded rod rather than have the entire threaded rod move into the pressure hull.  I tried this years ago and it leaked at the threaded entry into the piston (1/4" plexi).   Just a thought.

Mike

[bogstandard]

For a threaded shaft you should be able to make a threaded ferrule that is stuck onto the threaded rod in the correct position, so basically turning the bit that requires sealing into a round shaft. Then seal as normal.

John

[Martin (Admin)]

Hi Mike,

I've tried that in the dim and distant past but the piston eventually kept rotating the the cylinder.
How about soldering a short length of brass tube over the threaded rod where you need the seal?

[Martin (Admin)]

Snap! ... but  bogstandard it more technically correct!  ::)

[Subculture]

Yes but the piston has to move dynamically, so how will that work?

Ron Perrot made piston tanks that used a fixed rod and had a seal on the threaded shaft. This increases the friction quite a bit, so his tanks pulled a lot of current. You will also need to mount a limit switch in the wet area.

Personally I don't think making room for retracting rods is that much of a big deal.

Andy