About pressure rating of tubing

[Tony Lai]

Hi there.
I'm now working on my first fusor, but I keep failing to find those tubings (needle valve,tube fittings,etc) that are rated for 'high vacuum'. I have find some pretty good quality ones that are labeled to handle 25-40 Mpa of pressure, to my understand the atmosphere exerts 101.3 Kpa on a vacuum chamber, that is 0.1Mpa, far less than 25 so there tubings are sufficient to handle the job.
Is my gussing correct? Or is this complete nonsense? I really appreciate for any help.

[Richard Hull]

Any metal tubing with any wall thickness exceeding 1/32-inch is good for vacuum work. Of course larger diameter tubing than 1/2-inch will demand a thicker wall. Fusor shells can be only .040-inch thick, but 90% are stock .0625-inch thick. Remember, the maximum possible pressure in any vacuum system is only 14.7 PSI.

Richard Hull

[Dennis P Brown]

While many types of tubes/valves can easily handle the pressure differential (its, as Richard pointed out, very small), the issue that must be considered is leakage into the system by outside air. This is especially true for valves and any methodology to join system components. Cleanliness and lack of surface out gassing is also critical - one reason rubber hoses are an issue and while brass isn't used for high vac work. So copper tubing (just about anything suitable for just home piping) aluminum, or steel are common and just about anything available can handle that differential.