Carbon steel or stainless steel + flexible graphite combined gasket isusedforClassl50 gate valve; Stainless steel + flexible graphite wounded gasket is used for Class 300 gatevalve; Stainless steel + flexible graphite wounded gasket is used for Class600 gate valve and ring joint gasket is also optional forClass 600 gate valve; Ring Joint gasket is used for Class 900 gate valve;