... 25, ANSI B16.1, BS4504, ISO PN16 Wafer Type Double Disc Check ValveStandard:Design standard conform to: MSS SP-67, API609, ... API609, ISO5752 series 20, BS5155Test standard conform to: API598Design characters:Check valve is used for preventing the back flow of medium in ... the pressure of medium. When the medium is back-going, valve disc will close automatically to avoid accidents.1. Tightly sealed, ...