another normal sub sound, Tink, Tink?

[shawl@torchlake.com (Jonathan Shawl)]

I worked at a company for 6 years building vacuum heat treat furnaces. I saw the
same thing, we had to design the door and hinges so they could move in as the
o-ring compressed. The same it true on my sub the hatch latch becomes loose before
you get 10 ft of water overhead. A hatch hinge or latches needs to apply downward
force to seal the hatch and then allow it to compress all the way down to contact
with the hatch ring, otherwise you may have a leak or damage to the hinge.On my
first lake dive to 25', I was a little concerned to hear what sounded like a steal
on steal creaking sound as I started the dive. About every few feet I would here a
tink, tink. When I thought about it and checked to see what was causing it I
remembered the hatch hinge could do this as the metal plates slid past each other
a few thousandths of an inch at a time.
That brings up 1 more design consideration to think about, O-ring groves. You have
to have just the right size and shape groove to accommodate all of the o-ring
material (volume), so that when the hatch is compressed down metal to metal it
doesn't pinch the edges off the o-ring and damage it. I have seen this happen.
Also it can't be too lose or the o-ring will fall out or leak if the hatch ring is
not flat. Where I worked we found you could not go by the book sizes under all
conditions. The dimensions specked out in the o-ring seal books were usually to
wide and to shallow to work on doors and hatches, and the seal would fall on the
floor when you opened the door. Most of the time we would use our own dimensions.
Boy that was a long way to say "Yea, me too."

> Bang is a good description, I work with vacuum systems and I've had a small
> steel vessel implode.  Sudden, surprising and definitely not good for the
> stuff inside!!!
>
> I think the vaccum/sub test is a good idea!   I wonder, I've notice that
> fittings on the outside of vacuum vessels/pumps etc, can loosen when we pull a
> vacuum, due to the outside pressure compressing the o-rings/seals.  I would be
> curious to know if a similar action occurs on subs at depth?