The self priming centrifugal pump is designed to lift water from some level below the pump suction without having to fill the suction piping with liquid. It accomplishes this by creating a partial vacuum at the pump suction which removes the air from the suction line. The pump then releases the entrained air through itʹs discharge while retaining the initial fill of water in the pump case. It is this air / water separation is what makes the self primer different from a standard, end suction centrifugal. Try this with a standard end suction centrifugal and all you will get is a slug of water.