Plan 01 provides internal recirculation from the pump discharge area to the seal chamber, which is typically at a pressure slightly above pump suction pressure. Plan 01 is similar to Plan 11 in that it uses the pressure differential between pump discharge and pump suction to develop flow, but is different in that there are no external lines (piping or tubing) on the pump.  It is recommended for clean pumpage only and is typically limited to pumps with relatively low discharge pressure.