This is any valve with a free floating ring that is not locked to the screw rotation. These are most commonly 3-piece or 4-piece design Screw Tip Set.
The ring rotates only to the degree of drag-force created during screw rotation from contact on the forward face to the Nose body face (stud). The largest abrasion is on these surfaces and generally the impact of the wear of these surfaces dictates the useful life of the valve. The abrasion impact on the ring’s outside diameter is less, as ring rotation is generally below 1/3 of the screws speed.