Brake Question

At SVRy I ran across an automatic brake valve in our parts cache that remains a mystery. It is about the size and general appearance of a G6 or an H6, but has the number on it's nameplate of Q6B and is made by NYAB. It is definitly not an equivalent of an H6 as it is not designed with and equalizing piston. It is missing it's handle and I know that a spare H6 handle won't fit it. I do not know it's history. It may have come off #19 or #20 as I have now idea what was left of their brake systems in the cab when they came down from Alaska, though my understanding is that they originally had 6ET.