Patent ID: 8646752

Claim:
A valve assembly comprising: a housing having a passage formed therethrough; a valve ball having a through hole and disposed in the housing, wherein the valve ball is rotatable between an open position that has the through hole substantially aligned with the passage and a closed position that has the through hole substantially misaligned with the passage; a first seat comprising metal having a first sealing surface and a third sealing surface and disposed in the housing adjacent to the valve ball, the third sealing surface disposed in the housing adjacent the valve ball; a second seat comprising metal having a second sealing surface and disposed in the housing adjacent to the first seat such that the first sealing surface of the first seat is disposed adjacent to the second sealing surface of the second seat; and a stop shoulder comprising metal disposed upon a non-sealing surface of one of the first seat and the second seat such that the stop shoulder overlaps the other of the first and second seat, and such that a gap is formed between the stop shoulder and the other of the first seat and the second seat, the stop shoulder configured to engage the other of the first seat and the second seat to limit angular movement of the first seat with respect to the second seat; wherein at least one of the first sealing surface, the second sealing surface, and the third sealing surface comprises an arcuate surface.