Explanation on HPSOV

I got this for interview question, didn't manage to answer but the QE explain to me so, here is QnA session:

Q: When you do HPSOV valve change, after that you carry out engine run, op check satisfactory, why is the pilot still reporting the same HPSOV failed open in flight? Despite ground crew have been changing HPSOV and HP controller multiple time and everytime op check satisfactory on ground, why is it the pilot still reporting the same valve failed open in flight again?

A: Basically, on ground and in flight the HP controller and valve experience different baro (atmospheric pressure), if there is sense tube leaking in the HP valve or controller, due to it's sensing bellow, sensing lesser pressure difference on ground then in air, the leak is not easy to be detected on ground.

conclusion, actually doesn't make any sense after tracing the schematic diagram but then, i believe he was giving real life example, so lesson learnt is that next time if there is pneumatic valve faulty, remember to check on sense tubes, basically all the tubing for connection integrity and leak.

-alvin