On Sun, 20 Jan 2008 00:15:08 -0500, Red wrote:

..er.... It takes about 6 psi EXCESS pressure like 13 ft depth of
water to actuate the sprung knife?

Clear on up to outer space, there is no excess pressure I know of.
Or am I missing something?

Brian W

I take it he meant that it may be there to release pressure *inside* the
case to keep the case from "exploding" in a low pressure environment,
not imploding as would be the case of external pressure when sinking.
Red


Yes, I see that possibility now.
In practice, containers can usually take several times more
internal over-pressure than internal under-pressure.
Take a look at your clear plastic soda bottle. It may go higher than
60 psi before going bang, but 2 or 3 psi from outside will do a number
on collapsing it.

Brian Whatcott Altus OK