A volute shaped pump casing for a centrifugal pump includes a chamber for housing at least one impeller rotatable around an axis of rotation and a volute shaped chamber which forms a flow channel and which contains a splitter rib for dividing the flow channel formed wherein in a section perpendicular to the axis of rotation a mean camber line is positioned equidistantly between an inner and outer surface of the splitter rib, where the thickness of the splitter rib is varied along the mean camber line and for the mean camber line unwrapped to a straight line there is a maximum in the thickness, s, of the splitter rib, wherein said maximum is positioned at a distance L from the leading edge of the splitter rib, and wherein the distance L is in the range between 1.4 times the maximum thickness s and 6 times the maximum thickness s.