The water pump impeller on a boat is a crucial piece of equipment that allows the water pump to pump water through the motor to keep it cool. The impeller is a rubber turbine that, when it turns, creates a vacuum in the pump body and draws water through the pump and the rest of the motor. Replacing the impeller is a common maintenance procedure as over time it can become cracked and worn.
Step 1
Examine the bottom of the motor and find the four mounting screws holding the bottom shroud on. Use a screwdriver to remove the screws and disconnect the wiring harness inside the shroud.
Step 2
Slide the lower shroud off of the motor and then clamp the lower shroud in the vice. Locate the water pump housing (shaped like a silver bell) and use the socket wrenches to remove the mounting bolts around the corners. Slide the housing up and off of the transmission shaft and the use a set of pliers to pull the impeller out of the housing.
Step 3
Insert the new impeller into the housing and slide the housing back down the transmission shaft. Remount the housing with the mounting bolts and then slide the lower motor shroud back into place on the bottom of the upper motor shroud. Make sure to reattach the wiring harness and then secure the motor shroud with the mounting screws.
Impellers of pumps are classified based on the number of points that the liquid can enter the impeller and also on the amount of webbing between the impeller blades.
Impellers can be either single suction or double-suction. A single-suction impeller allows liquid to enter the center of the blades from only one direction. A double-suction impeller allows liquid to enter the center of the impeller blades from both sides simultaneously. The illustration below shows simplified diagrams of single and double-suction impellers
Impellers can be open, semi-open, or enclosed. The open impeller consists only of blades attached to a hub. The semi-open impeller is constructed with a circular plate (the web) attached to one side of the blades. The enclosed impeller has circular plates attached to both sides of the blades. Enclosed impellers are also referred to as shrouded impellers. Figure 5 illustrates examples of open, semi-open, and enclosed impellers.
The impeller sometimes contains balancing holes that connect the space around the hub to the suction side of the impeller. The balancing holes have a total cross-sectional area that is considerably greater than the cross-sectional area of the annular space between the wearing ring and the hub. The result is suction pressure on both sides of the impeller hub, which maintains a hydraulic balance of axial thrust.
