Sent: Tuesday, April 27, 2004 5:14
AM
Subject: Re: [PSUBS-MAILIST] hatch
squeeze
Brian,
As I recall you got a Parker O-Ring Manual, correct?
In it, or any other manuals on O-ring applications, you will find
either tables or recommendations for O-ring squeeze. It's the
difference between the O-ring thickness and the thickness of the remaining
groove when the two mated surfaces are put together. Follow the guide
for a "Static Application." They usually give the example of a flange
seal where two pipes are joined together with bolted pipe flanges.
Your hatch is the same thing.
There is one alteration to the standard groove that
is helpful in a hatch seal. When machining the inner diameter of the
groove for the O-ring, it helps to put a bit of an angle on it sloping
into the groove to better retain the O-ring when the hatch is opened.
Put about a 10 degree angle on the inner diameter wall and size the ring so
it is a bit smaller then the diameter of the groove so it snaps in similar
to an elastic band around a rolled up bunch of papers. Not so much
stretch as to reduce the cross section of the O-ring but enough to hold it
in the groove.
How are you going to machine this on a table? Either
chuck it in a lathe, or a rotary table on a miller or a machining
center.
Brian, I don't want to sound critical, but are you sure
your ready for welding parts together? It's real easy to work
yourself into an expensive corner if your assembling before you have the
design details worked out.
Good luck, Dan H.
----- Original Message -----
Sent: Tuesday, April 27, 2004 1:50
AM
Subject: [PSUBS-MAILIST] hatch
squeeze
Hi All, Been working on my hatch, had the ring
welded on to the hemisphere by my neighbor ( who did the most professional
weld job I've ever seen ! ) . Anyway, spent the afternoon fitting up
a support table so I can machine the hatch cover true and flat. As
it is it's only 30 thousandths off. Then I will need to machine the
hatch seat. Since I have never actually seen a hatch, other
than in pictures, I feel at a bit of a loss as to
certain aspects of the hatch. Like I need some type of "o" ring
right? Or will the hatch seal if self if both mated pieces are
perfectly true? I'm having a little trouble with
physics of the hatch seal. With an "o" ring , like in a thru hull
fitting, the sealing action of the "o" ring works because water pressure
is pushing the rubber "o" ring tight against the surrounding wall,
But with the hatch you have the large area of the hatch pushing the whole
hatch against the hatch seat - the "o" ring or gasket is not acting the
way it would be in a thru hull fitting. Would the specs for the
squeeze on "o" ring be different than on a thru hull fitting? Any comments
would be greatly appreciated.
Brian Cox