Camille,
Suggest that you investigate the ASME standard for Graphic symbols:
ASME Y32.11-1998
"Graphic Symbols for Process Flow Diagrams in Petroleum and Chemical Industries"
Most companies incorprate this group of symbols into an in-house standard, then require everyone to use the "enhanced" standard. There must be other sources on the web..... including a free AUTOCAD symbols library
Good Luck
MJC