Shotblasting machine model PWH is suitable for the cleaning of the internal surface of water heaters before enamelling. The cabin is designed to allocate up to 12 stations in line; water heaters are hanged on overhead conveyor and stop in each station (single pass movement) or in alternate stations (double or triple pass movement). In each station, a centering device permits the alignment of the water heater central hole with a blasting/blowing lance. The lances enter into the water heater and rotate in order to permit an homogeneous treatment of the internal surface. The shots are collected and delivered to a recirculating system. The correct number of stations are defined according the desired production rate.