Check valves prevent reverse flow via spring-loaded single or dual discs, swing discs or ball mechanisms in wafer, flanged or threaded bodies. Ductile iron, WCB, brass or SS304/316 with EPDM/NBR/PTFE or metal seats ensure silent non-slam shutoff, low cracking pressure and corrosion resistance. Sized DN15–DN1200, driven purely by flow—no actuator. Fits water, sewage, oil, HVAC and pump discharge under DIN/ANSI/JIS.