RE: Weird UP-3 valve problem
Arnaud:
Probably the plunger needs to be lubricated, the friction is not allowing it to move al low pressures and a dry o-ring would leak air, there is a door on one of the sides and a small hole on the opposite side, remove the 2 screws on the perimeter of the door and with a properly thin piano wirewith a SMOOTH END, insert it through the hole on the opposite side and push the plunger and door out, watch out for the spool and spring, lubricate o-rings with silicone grease ONLY (Dow #55) and reinstall