The flexible impeller pump working principle consists of a rotating rubber impeller with supple vanes attached that maintain contact with the pump inner walls. As the casing is actually smaller than the vanes, they must bend and then straighten as the impeller turns to conform to shape of the pump internal walls. The vacuum caused by the movement of these vanes push the fluid round from the inlet to the discharge pipe. As the space between each vane and the pump casing creates it’s individual chamber, the flexible impeller pump head essentially has several chambers within in, all operating like valves. Hence, it’s self-priming ability.