LittleInch,
"0 bara"? With which accuracy or tolerance?
Sharikkhan,
in my opinion the expression
“full vacuum” alone has no technical meaning (more or less like…
“zero leakage” 
).
The minimum operating pressure should be defined (in terms of absolute units).
In general terms, several vacuum grades are usually defined (low, medium, high, ultra-high, etc…) corresponding to certain pressure value ranges, and different design choices (
e.g.: surface finishing, gasket types, materials selections, etc.) may be applicable to each one.
See, for instance:
-
;
-
;
-
.
In more particular terms, as far as I know, industrial valves for oil & gas applications (
e.g.: distillation stages in oil refining) usually work in the “low” vacuum ranges,
i.e. not below 1 mbar
a, approximately.
Valves may also face lower pressures (
i.e. 0.1 mbar
a or less) during factory testing whenever a check with a “vacuum hood technique” is required (see ASME B&PV Code, Section V, Article 10, Appendix IX).
However, it’s always better to check it all out with the Engineering Company and/or End User, of course.
Hope this helps,
’NGL
