Had hydro certification done on bottle #4 (crew bottle, location aft right), but made the mistake of pulling #2 (passenger bottle, fwd right) first.
Noticed when larger brass line was loosened on the #2, a continual bleed occurred. Two Gulfstream mechanics were onsite and they mentioned that the paired bottle's fitting also needed to be removed. When it was..... all bleed-off stopped.
I learned that these two line are tied together with a "T" fitting. They hook to a bottle fitting with an internal Schrader valve. It is not until the brass line has been backed off that the valve shuts. This valve "is not" controlled by the bottle shutoff. Great........ I learned something. (One final note: The bottle pressures equalized with each other when the large brass lines were installed.)
I pulled #4, but when I disconnected the same position brass fitting..... no air????? When the bottle was returned, I hooked everything up. I had no pressure indication in the cockpit or fill point. I had plenty of flow to the masks. WTF?????
Upon pulling the brass fitting on #3, it was found not seated. My initial seat on #4 was bad also. Both were corrected.
In this case, before anything was dicked with, the crew pressure indication was only the #4 bottle, but mask flow was present for both.
I did a hand drawing of what "should be" the correct bottle output fittings. Please correct me if this is wrong.