(under subclass 318) Devices in which either the reciprocating head element or the cooperating seat is provided with an additional sealing gasket so that when the valve is closed, a nonresilient seal (generally metal to metal) is formed as well as a seal between the gasket and the nonresilient structure with which it engages.
SEE OR SEARCH CLASS
137, Fluid Handling,
516.29, for this structure in direct response valves.
