Many impeller based water pumps, not to be confused with powerheads or propeller based water pumps, found on our various aquarium equipment don’t always operate perfectly right out of the box. These centrifugal pumps rely on water pressure and motion to draw in more water, and if they are not primed correctly, they will rattle violently and seem not work at all. To remedy this, many pumps need to be primed. This means that the pump and a majority of the associated plumbing are flooded with water. As soon as the pump is turned on, the spinning impeller evacuates the pump’s housing and creates a negative pressure drawing in even more water.