I have a schematic for some gas lines in a wafer processing unit. One of the symbols which occurs is a circle with an x in it that has the left and right quarters filled in to form two black triangles. (I've attached a drawing.)
From context, i can tell that these represent valves to allow or block flowing of the gas. However i would like to find this symbol in some guide to give a more exact interpretation of the meaning, and just to have an authority that i can cite to.
I have not found the symbol in the context of a gas line schematic in any online reference.
Where, and how, can i look?