In our plant, the process flow diagram is only as detailed as necessary to define individual process streams. For example, for a pair of pumps, only one is shown. For a bank of exchangers, only one is shown. For a control valve station, the bypass is not shown. Flanges, bleeds, drains and not shown. The P&ID, on the other hand has all piping and instrumentation components shown. It should include every flange, every valve, every instrument, every reducer every exchanger and every pump. It should include all piping connections down to the drains and bleeds.
Johnny Pellin