----- Original Message -----
Sent: Wednesday, March 17, 2004 9:04
PM
Subject: Re: [PSUBS-MAILIST] thru hull
stress
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