A part used to turn on and off a pipe.
Valves can be found in Abandoned Ruins #2, in some chests in the Hazardous Ruins and by killing Chemical Dropout. Valves can also be found in the boxes in the Abandoned Ruins #3. The boxes normally have several items in them and every other box usually has a valve.
1 Carbon Steel Bar
2 Copper Pipe
4 Bronze Pipe