Johnson Pump F4B-9 Impeller Pump OEM - Flange Mount [10-24967-02]F4B 9 Impeller Pump OEM Flange Mount Flexible impeller pumps, F series, provide an efficient solution to most raw water pumping needs. The primary advantage of a flexible impeller pump is its self priming ability. As the vanes of the impeller are depressed and rebound, they create their own vacuum drawing fluid into the pump. A dry pump can lift the water up to as much as 3 meters. Thus a flexible impeller pump being used for engine cooling needs not