HPGRs consist of a pair of horizontal cylindrical rollers through which material is passed. The two rollers rotate in opposite directions, "nipping" and crushing material between them. A similar type of intermediate crusher is the edge runner, which consists of a circular pan with two or more heavy wheels known as mullers rotating within it; material to be crushed is shoved underneath the wheels using attached plow blades.High pressure grinding rolls have the capability to fill the roll of secondary crushers and primary/secondary grinders. Often applied as a replacement for conventional SAG milling circuits, they result in lower energy consumption, lower grinding media consumption and lower operating costs. They also tend to have a smaller footprint with easier installation.