A swimming pool pump pulls water from the skimmer and main drain and then pushes it through the filter and heater. The water is then pushed back into the pool through the return lines. The size of the pump depends on several factors, including the size of the pool and turnover rate needed. Above-ground pools require low-head pumps, while inground pumps use medium- or high-head pumps. This difference is critical for commercial settings.
To backwash the system, the flow is reversed by switching valves on the pump. The water is stopped from flowing back into the pool. Instead the water is pushed into the bottom of the filter.
The pumps motor can be single speed, two speed or variable speed. With a single-speed motor, the pump is always running. Two-speed motors are more energy efficient. A variable-speed motor allows the pump to be automatically regulated, based on demand. Pumps may be flooded-suction or self-priming depending on the installation and design of the site. Flooded-suction pumps are below elevation and will naturally flood if main drain, vacuum and skimmer lines are open.
The size of the motor is based on the pool size and turnover rate needed. If a pumps motor is too powerful, it can cause problems with filtration and damage the filter and heater. Its important, then, to match the horsepower of the pumps motor to the pump type and flow rate.