Flexible impeller pumps 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 water up to as much as 3 meters. Thus a flexible impeller pump being used for engine cooling needs not be located below the water line or manually primed. An added feature of flexible impeller pumps is that they can pass fairly large solids without clogging or damaging the pump. This reduces the need for filtering the incoming fluid.
For general raw or fresh water applications, the standard long lasting neoprene rubber impeller is used.
A general feature of all flexible impeller pumps is that they cannot be permitted to run dry for more than 30 seconds. Both the impeller and the seals depend upon the water for lubrication and will soon burn out if run dry. Wearing parts are easily replaceable, and service kits are available for all standard models.
The flexible impeller in the pump, which provides the pumping action, is a wear part. Over time the impeller will lose its ability to maintain the pressure needed for the flow of cooling water. For an impeller of lesser quality the performance can degrade so rapidly that you, at best, must replace the impeller more often, at worst, you could be left adrift with engine damage. Wearing parts are easily replaceable, and Johnson Pump service kits are available for all standard models.