Re: CRT implosion screens.
I run a high vacuum system which consists of a 12" diameter 14" high borosilicate glass bell jar resting on a 1" thick steel plate. The glass is sealed to the plate by an "L" seal made of a special low vapour pressure rubber. The chamber is evacuated first by a fast roughing pump. That removes the majority of the air and gets down to 1 torr in a bout 20 minutes. After that the backing pump is started, then the high vacuum vapour diffusion pump when the pressure is less than about 50 milli-torr.
It is worth noting that the 1 torr "rough" vacuum is every bit as dangerous as the high vacuum. The difference between the force on the glass at high vacuum (1*10E-05 torr) and rough vacuum (1 torr) is miniscule.
If you do the sums, working out the area of glass and the pressure on every square inch it comes out at about 2 tons on the bell jar - say a large family car. I guess its about the same as a large CRT. I am protected from it by an acrylic safety cylinder - just in case. The most likely time for it to implode would be on pump-down. The bell jar looks like it was blown, and has some visible imperfections (bubbles). I've been using it for years now, but I never run it without the implosion shield.
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