This is a vortex diode or Zobel diode, apply flow in one direction and it will pass fine(center port to side port), apply flow in another(side port to center port) and a vortex will be formed in the chamber increasing resistance to flow.

For more info vortex type fluidic devices and fluidic devices in general see: http://www.tippettsfountains.com/fluidicsbasics.php?width=1920&height=919

Bolt both plates together using M5 bolts or print as one piece. Connect to other fluidic elements using 5/16" tubing.