5 bar mate must of been a spellie.The air should only come out of that hole when the valve has switched over from being being in the relieved state ie decompressor valves open to when it starts pumping again and it should just be a short burst to unload the decompressor valve heads.
I would disconnect the pipes to the tee where it splits to go to each and see if any air comes out of either it might be one has a diaphragm gone ?
Banny are you sure from your first post that it put 50 BAR into the 127 ltr tank because that is 700+PSI.
Yes in the decompressors /unloaders on the cylinder headyou mean a diaphragm in the valve heads not the pilot valve.
differential