it protects against, or uses, surges in some carb types?
For Y'all who wonder what the *** the surge diaphragm is: It is tha part inserted between the fuel pump side cover, and the pump diaphragm. I have never seen it in airplane engine carbs, but it is listed as part #33 in the Walbro WT manual. It must have some use in some carbs, or Walbro would not list it.