Here is another light build and comparison

[Ed Palma]

So pressure test failed! I don't know if the plug is leaking or the o-rings are the problem. Back to the drawing board!

You could put it in the pressure pot just up to the body and exclude the gland. That way you can rule out the o-rings.

 

[Ed Palma]

BeasleyM,

DIWdiver answered the question in lens strength in this thread:
Acrylic Thickness

350xfire -

From Marks' Standard Handbook for Mechanical Engineers, the max stress in a disk supported uniformly around its edge is S=1.24wr^2/t^2, where:

S = max stress, PSI
w = pressure against the plate, PSI
r = diameter
t = thickness

Substitute the flexural strength of glass as 69MPa, and there you have it

 

[beasleym]

DocEd
Thanks very much! Just what I was looking for and couldn't find in my old college books.

Couple of comments:
1) Confirmed the mpa of borosilicate as 69
2) from the link for calculating stress using the mpa - I get 1007 lbs/sq.ft. (Conversion Calculators - Convert MPa to psi- Chapel Steel)
3) there is an error in the thread, r should be radius. Using 90 lbs pressure (roughly 200 ft depth), 1.085 inches radius, .197 inches thick, gives a pressure stress of 615 lbs. So the safety factor at 200 feet is 1.6

I might switch to acrylic for the additional safety and not having glass to break.

Again, thanks!!