This is the insde of the intake diverter valve B. The section that includes the two openings (one to the left, one straight ahead) is machined in an arc. There's a pivot arm with a curved plate on the end, turning the valve swings that across one or the other of the pipes to block it off. This one doesn't turn, but since it's brass it's probaby just jammed by some of the debris in there.

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