MAAG GEAR WPU Gear Unit The two series of our MAAG GEAR WPU Gear Unit ensure that your vertical roller mill has the dependable drive system you need, whatever your required power range. With specifications to ensure safe operation in coal mills, our two-stage gearbox has you covered. We developed the small series of MAAG GEAR WPU Gear Units specifically for coal mills in cement, mineral and thermal power plants. The unique requirements of coal mills demand that the coal grinding system considers the heat sources used to dry raw coal, as well as the fire and explosion hazards of coal dust. To meet these demands, the entire grinding plant must be shock-resistant and have explosion relief valves.