QXS Bridge type suction machine adopts mobile bridge type. It stops at the inlet side when not at work. Skimming plate are placed down to collect and scrap scum to the skimming tank during down-flow operation, skimming rake are lifted up to keep away from surface in case of scum retrogradation. Sands at the bottom of the tank are discharged to the collecting tank by suction pump through suction pipes, and flows to the grit-water separator for next processing. It works repeatedly to achieve the aim sand suction, collecting and discharging.