The Type 591/595 Vent and Vacuum Breaker Valves shall be true union and fully serviceable. The float shall be of conical shape and stabilized by a guide rod.  The carrier shall be adjust-able and reverse threaded.  The valve nut threads shall be of buttress type.  All elastomeric seals shall be of like material.  ANSI flanged versions shall meet ANSI B16.5 150lb standards.  All valves shall be tested in accordance with ISO9393 and designed to ISO16137 standards.  All valves shall be manufactured under ISO9001 for Quality and ISO14001 for Environmental Management.  Following assembly, every valve shall be tested and certified bubble-tight exceeding Class VI standards.  PVC valves shall meet ASTM D1784 cell classification 12454 standards.  CPVC valves shall meet ASTM D1784 cell classification 23447-B standards.  PP valves shall meet ASTM D5847-14 cell classification PP0510B66851 standards.  ABS valves shall meet ASTM D3965 cell classification 42222 standards.  PVDF valves shall be type 1, grade 2 according to ASTM D3222 standards.  Valves of all materials shall be RoHS compliant.