Yes, several people know that. Oh, would you like someone to provide the information you didn't ask for? Sure, I can take a stab at it.
Generally, company policy controls. Some companies prohibit it, some allow it, the vast majority are silent. As far as I've been able to find, the codes tend to be silent. Again, this one comes down to Engineering Judgement.
Few valves are truly bubble tight, so testing against a valve can cause a steady bleed off that looks like a leak (remember that in a pneumatic test, a leak looks like a spring slowly uncoiling instead of a rapid depressurization like you would see with a hydrostatic test). If you are using air or nitrogen for your test media, you could easily cause serious process problems on the other side of the leak.
I always install skillet blinds on the test side of block valves. You have to be REALLY careful to get the thickness right because it can be impossible to remove the wok you made by pressurizing a skillet that is too thin (the time I missed a decimal point we had to blow down a couple of miles of 12-inch line to drop the block valve to remove the wok).
No, the handle was too rough, but I kept in my "how stupid are you" collection until my office mate got sick of barking his knees on my rusting metal and he threw it all away (the prize of the collection was five 6-inch 90 degree elbows close coupled out of plane with a flange on both ends, pretty sculpture but very heavy). The "wok" was about 13 inches across, about a 1/2 inch flange all the way around and 3-inches deep--a perfect chord of a sphere.
API 598 requires a low pressure Air seat test for most gate valves. It's an optional test for Globes and checks. That would be a pneumatic test on a closed valve.
That is true. I got the feeling that he was talking about a system strength test, but I could easily be wrong. His original question was quite lacking in details.
