Check valves are one-way or nonreturn valves that open with fluid movement and pressure, and close to prevent backflow of the pressure to upstream equipment such as pumps and compressors. In fact, check valves allow the fluid to flow in only one direction. Water hammering and slamming is one of the operational problems associated with some types of check valves which are explained in this chapter. Different types of check valves such as swing check valve, nonslam axial check valve, piston check valves are available