> etc etc to a point of where 495' is 235.2 psi That is a lot of pressure
> on plastic not to mention the seals and glass mounting for the cover. If
> you

I have heard of, and have recommended to others, using a scuba air tank
for this, with a very small window. In theory it should implode slightly
below design pressure which can be 400at (this means it could stand 4000
meters and twice as much with counter-pressure - I don't think so - but it
will surely stand 150). It is also easy to test if you have a boat (I did
not do this).

Peter

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