(under subclass 318) Devices in which both the head and seat surfaces which constitute the valve interface are so constructed that they mutually cooperate to produce the valving action.
(1) Note. Patents have been placed here in which the peculiar construction of the head requires a particular configuration of the cooperating seat, and vice versa, (i.e., the head would not successfully operate with a conventional seat, e.g., a conical seat, a planar seat, etc.) or in which the mode of operation of the valve depends upon a specifically contoured head or seat to produce some unexpected result.
