Plain Black NRV Piston Type with soft seating offers better leak tightness than those with metal-to-metal seating. Combination seats that have a metal seat ring and a robust insert also offer better leak-tight properties. The angle between the seat and, therefore, the vertical plane, can range from zero to forty-five degrees. Plain Black NRV Piston Type is easy to handle. When a swing check valve goes to either a fully open or fully closed state, the disc becomes unguided.