A valve that is a valve where the closure member is a gate or disc with a linear motion parallel, or nearly parallel, to the plane of flat seats, which are transverse to the direction of flow.
The gate closure member shall be of one piece (i.e. wedge or slab) or constructed of two or more pieces (i.e. double disk). API 6D March 31, 1994, Sect. 4.1.1.a.