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what are the spec. vacuum requirements for thermos bottles? Answered

I want to do some experimenting with making thermos bottles.
I know that a vacuum is needed but how much?

I heard that the thermal retention value only works below a certain vacuum level but I don't know what it is. any small vacuum won't do.
I also would like the answer in regular terms.

I found out that solar tubes use
P<5x10-2Pa of vacuum. I don't know what that means in inches of vacuum. I need to know more, so that I can buy the right vacuum pump.

What other equipment will I need?
will a regular check valve and epoxy work for testing?


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Best Answer 10 years ago

5 x 10-2 Pa isn't very low, but I'm guessing those solar tubes are discharge lamps of some kind.
You'd want to be down to ~0.1 Torr or 4 x 10-3 inches Hg at least, or in regular terms get a reasonably good vane-pump.



10 years ago

.  Try this Pressure Conversion Table.
.  When dealing with a vacuum, you need to use special lubricants and sealing oil(s). Your check valve should use vacuum-rated elastomer seals, but, for short-term use, you can probably get away with a "regular" check valve. Most epoxies should be mechanically strong enough - you'll put <15psi on it at max - but porosity may present a problem with some of them.