A vacuum-assisted self-priming centrifugal pump is made up of two pumps, an end suction or split casing pump and a diaphragm pump. When there is no water in centrifugal pump, the diaphragm pump will operate to remove air out of the suction line until the pressure in suction line is less than atmospheric pressure which allows liquid to flow into pump. When there is sufficient water in the pump, which means it’s primed and ready to pump, diaphragm pump continues to operate on low power until it’s required again. If pump ever loses prime or there is no liquid left, the process starts automatically again.