Proper centrifugal compressor symbol should be selected first, as shown in figure-1. Normally, a centrifugal compressor is accompanied by a Knock Out Drum (KOD) at the compressor suction and an aftercooler at the compressor discharge, as per a typical compressor PFD. Symbols for these equipments should also be placed on the P&ID before proceeding ahead. All the equipment symbols should be selected from the legend sheets of a particular project.