This picture shows the main parts of the pool pump in a pump cut-away. These parts include: the strainer basket cover that provides access to the strainer box to add water and clean out debris; the strainer basket that filters the larger pieces of the debris; the diffuser that direct water to and collects water from the impeller; the impeller that generates water pressure through centrifuge; and the motor that drives the impeller. Also shown are the two ports where water enters into the pool pump from the pool and exits out or the pump to return to the pool.
This picture shows the basic flow of water through the pool pump. Water is sucked in through the basket, through the center of the diffuser (yellow) and through the center of the impeller. As the impeller spins, the water is thrown out the outer slots of the impeller where it is collected by the diffuser. The water is then funneled though slots in the diffuser into the high pressure water chamber and then out the exit port to the pool. Two notes: this picture shows a cut-away of the pool pump so that you can see the internal parts of the pump. In a working pump the diffuser would completely enclose the impeller. Also the only moving part in this pool pump is the impeller driven by the motor shaft. It's centrifugal motion is what sucks the water in and pushes the water out under pressure.
This picture shows the inner operation of the diffuser with the diffuser partially pulled off. The diffuser funnels water from the strainer pot into the center of the impeller, then collects spun water from the outside edges of the impeller and releases the water through its own slots into the pressured chamber (dark blue arrows).
This picture shows the operation of the impeller. Water enters the center of the impeller. As the impeller is spun by the motor, a series of blades, like a fan, push the water to the outside edges of the impeller where it exits through slots to be collected by the diffuser. It is this centrifugal force that generates the high pressure of the water exiting the pool pump.
The strainer gasket usually sets in a groove on top of the strainer pot and provides a seal for the strainer pot cover. A poor strainer gasket will allow air to be sucked into the pump and prevent priming. The instructions for replacing a pump lid O-ring are included in the following guide: How To Clean Out the Pump Strainer.
The diffuser gasket provides a seal between the strainer pot and the chamber around the diffuser and impeller. This chamber collects the pressurized water that is released through the output port. Without this seal the pressurized water will blow back into the strainer pot and the pool pump will loose pressure. For instructions in how to replace a diffuser gasket go to How To Replace Pool Pump Gaskets.
The housing gasket provides the seal between the motor assembly and the pool pump assembly. If this seal is bad, the water will spray out of the pool pump and you will loose pressure and water. For instructions in how to replace a housing gasket go to How To Replace Pool Pump Gaskets.
The motor shaft seal prevents water from leaking out of the pressure chamber along the motor shaft into the motor assembly. When this happens you will see water dripping from the bottom of the motor. For instructions in how to replace a motor shaft seal go to How To Replace A Motor Shaft Seal.
If you are repairing your pump or pump motor consider purchasing a GO-KIT. Each GO-KIT contains the replacement seals and gaskets you will need to repair your pump. A typical GO-KIT like the one pictured here for a Hayward pump, contains the motor shaft seal (2 parts), the pump housing gasket, the pool pump lid o-ring and the diffuser gasket. Note: These GO-KIT are generally unique to the make and model of the pump. Order the GO-KIT specified for your pump's make and model.