The SVC/SHC Series were the first check valves to follow the valve design guidelines of ASME BPE 2009. Since no spring, hinge, mechanical return mechanism or stem is used, they are crevice-free, have no areas for particle entrapment, minimize particulate shedding, and are fully drainable. As soon as inlet pressure exceeds the weight of the disc plus the outlet pressure, the disc will lift. Process media flows under the seat and through the disc perimeter holes to the outlet side of the valve. As flow begins to reverse, the differential pressure across the valve drops and the disc returns to the seat, closing the valve.