I think I should mention the reason I never continued any further with this system when I returned home. The main problem was the expense of purchasing a quality vacuum pump and control gear capable of producing vacuums of 3 bar and over and keeping it stable for an extended period of time. The pressure vessel was not a problem to assemble from a length 6 inch diameter 3/8 inch wall steel pipe welded shut at one end having the vacuum pipe inlet fitted also a vacuum release valve and at the other end a bolt flange fitted with a steel closing plate and rubber gasket for access.

The only lessons in my life I truly did learn from where the ones I paid for!