The Symbols are identical unless they show an "ENERGY TRIANGLE," like in a Solenoid/Pilot Operated valve. Then the only difference is the Outlined Triangle for pneumatics and a Filled Triangle for hydraulics.
You can see my take on Fluid Power Symbols in Chapter 4 of a book I wrote to teach Fluid Power Basics. I show the symbol and a representative Cutaway of a typical valve the Symbol might represent.
The second book is for an advanced Circuit Design class for anyone who has completed the basic class or who knows how to read a Fluid Power schematic drawing.
