Krzysztof Kożurno (asker) Jun 28, 2015:

Witold Please post your suggestion as an answer so that I can close this. Your suggestion is very good.

Krzysztof Kożurno (asker) Jun 17, 2015:

It seems to be a valid point, Witold. I have some more relevant context for this.
The original filling in the factory is made to a pressure of 20 kPa (0.2 at, 3 psi) at a temperature of about 20° C (65-70° F). This pressure will change with the ambient temperature. Even at -25° C there shall be a small positive overpressure, and in a warm climate the pressure still stays within, say, 30 kPa.

The thing is these documents are far from word-perfect. Still, I believe this is not some minor mistake and to write "positive overpressure" rather than just "overpressure". So in spite of minor mistakes, you can assume that this is valid and correct. And logical to expect pressure to rise as temperature rises.

Witold Palka Jun 17, 2015:

Positive pressure or overpressure should be enough. There is one situation where positive overpressure could make sense. Provided a pressure reference level given at ex. 5kPa, 4kPa could be negative overpressure. The value of 4 is negative compared to the limit, but still in overpressure range.

Łukasz Rojko Jun 17, 2015:

See - https://books.google.pl/books?id=F3q59-hcGDoC&pg=PA367&lpg=P...