Brian,
You can contact "Parker" and request a copy of their O-ring
book or maybe find something on line. They're are many manufactures of
O-rings and any one of them should be able to supply you with a book of
standard sizes and tolerances. Parker makes all types of packing and
seals. They might not be to anxious to send out a book to a guy for one
time use but they do have some good literature.
You don't need ten thousandths clearance between the shaft and
through hull. As long as the shaft moves freely it's not to tight.
The greater the pressure your trying to seal, the closer tolerance though.
In 3000 psi hydraulic applications, you wouldn't want more then a thousandth or
two clearance or the ring will extrude. At 300 feet depth all you have is
150 psi so you can have up to maybe ten thousandths clearance but it's not
required. I would keep clearance down to a thousandth or two no matter the
pressure.
If you pick a standard fraction of and inch shaft size you
will find an O-ring to fit. An O-ring guide will give you the groove size
and help you pick a ring. Most guides are divided into static and dynamic
applications. You want dynamic, of course.
Don't make the thruhull to short. It's a good idea to
make it long enough so the shaft won't bind if it has any side loading. I
would make the through hull's length about four times the shaft diameter and
more if I had room. Designing in two O-rings on each through hull is a
good idea also, since it's a sub.
Your correct in not creating a situation where the O-ring gets
cut when inserting the shaft. All you need to do is deburr the ends of the
hold a little. Scrape the corners and touch it a little with sand paper
while it's in the lathe and that's it. If your O-ring is to be installed
in the thruhull, just round the edge of the shaft end your going to
insert.
I use an old O-ring guide I've had for years and used it
quite regular. If you can't find what you need, let me know and I'll
either copy you the part you need of look around more for a source.
Regards,
Dan H.
----- Original Message -----
Sent: Wednesday, March 17, 2004 8:56
PM
Subject: Re: [PSUBS-MAILIST] thru hull
stress
OK , I think I'm on the right track now.
Machinery's Handbook, fits and O
rings all the info is right there I just have to read it
dah sorry for the ranting
Brian
----- Original Message -----
Sent: Wednesday, March 17, 2004 8:12
AM
Subject: [PSUBS-MAILIST] thru hull
stress
OK, I'm having a thru hull stress out.
I've learned so much in the past year
I've been with this group and I would like to thank everybody. This is
an incredible group of people. The core group who started this
forum along with everybody else have really enriched my life
measurably!! Just wanted to make sure I said that if I
haven't said it before. I've learned to operate the lathe and
mill along with many other skills of measuring and so forth. And as an
added benefit as well is that I have the whole new area of
machining to talk to my Father about. He was/is a hydraulics engineer,
we have always talked tech but now there is an added dimension to
it.
I'm still learning however, it's amazing to me how
when you jump into something how you encounter the problems head on,
something your not going to get working on Auto Cad!! I am still
not entirely clear on this thru hull assembly that I'm trying to do. I
machined this part but now it is becoming apparent that I should have first
obtained a standard "O" ring and made the shaft based on the size of
the "O" ring that is off the shelf so I'm not fighting correct tolerance
problems. The other thing I'm in a quandery about is the fact that the
"O" ring needs about 10 thousanths space between the shaft and the
hole. It seems to me that this is going to create a bit of slop when
turning the valve handle once the thru hull is in place, hence the need for
a concentric larger diameter shaft with closer tolerance that does not have
an "o" ring. or maybe reduce that diameter just near the "o"
ring. Also the fitting or female part where the shaft goes into needs
to have a rounded or tapered hole so the "o" ring does not tear when being
inserted into the hole. And I'm not sure how long I should make the
part, how much it should protrude on each side of the 1/4"
hull. Anyone have some thoughts on
some of my quanderies?
What I might do is proceed with what I think is right and then put up a
picture of what I've got and get some reaction from the group. Thanks
all !!
Brian "stress-out" Cox
|