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Re: [PSUBS-MAILIST] O rings and pressure
Brian,
I see you already have good recommendations for some O-ring
information sites. I would like to comment on some of the other
recommendations you were given though.
True, many times an O-ring is installed in the shaft rather
then the housing. As was mentioned, It reduces the effective diameter of
the shaft though and caused critical stress points because of the nature of the
O-ring groove itself. Also, if you require a .500 inch diameter
shaft for the torque your applying and groove the shaft, you have to use a shaft
of maybe .625 or .750 inch to have .500 where the groove is. The
larger shaft size is like a piston in your hull. With the water pressure
on the outside and ambient pressure in the inside, the larger shaft
diameter has greater longitudinal forces on it and will be harder to
rotate at depth.
Machining internal O-ring grooves is more
difficult then machining grooves on a shaft but polishing a bored
cylinder is more difficult then simply buffing the shaft to a
smooth finish.
For most through hull applications put the grooves in the
housing not the shaft.
I also think you should use a high pressure
regulator on your air supply. If find a time when you need 2000
pounds pressure to blow ballast, your in deep ( I wasn't thinking water
here). Regulate your air pressure down so you can blow
ballast at depth with some extra pressure for a safety
factor. The HP air won't freeze since the majority of the
moisture is removed if you have them filled at a dive shop. But you
just don't need to work with that high pressure in a P-sub.
Dan H.
----- Original Message -----
Sent: Wednesday, November 19, 2003 10:07
PM
Subject: [PSUBS-MAILIST] O rings and
pressure
Hi, I have a dumb question, I just machined my first
sub part, sort of a test part, a thru hull piece that will have a shaft going
thru it to turn a valve from the inside of the sub to the out side. I
machined an inside groove for an "o" ring, now are there
recomended specs for this "o" ring ? Like so many thousandths thickness
etc.. and should the shaft be notched as well?
Second dumb Question: Is all of your air pressure comming off
the high pressure cylinders (2000 psi) always dropped down to a lower
pressure (200 psi) with a regulator before it is used to blow out a
ballast tank? Is that high pressure too high to use for that (possiblly
freezing up lines?)
Brian Cox