PID Controller Design

Hallo , I already design PID Controller for water process , flow trigger pressure. The case is 3 state , for example flow < 0.2 l/s then pressure 0.2 bar , flow > 0.2 l/s then pressure 0.7 bar , flow > 1.2 l/s then pressure 1.2 bar. Transition from state to state not smooth (hunting). Anyone had experince same me? Please advice