Replacement Valve is a written note found in Dishonored
Would you see to it that this valve gets installed in that little supply depot by the loading docks? The men have been grumbling about this thing for what must be months now, as if there were anything of value on the other side of that door it's supposed to open. Keep quelling problems like this for me and you just might make apprentice.
High Artificer Bartholomew
It can be found in the locked workshop in the mission High Overseer Campbell, alongside the titular replacement valve.