Try google - when I was researching valve stem solutions, I ran across at least one product like yours. As I recall, I think it said it would equalize pressure, but would not allow total loss of air in the event of a blowout on one of the linked tires. If you can figure out what brand you have, you may be able to verify whether you have a similar setup...
By the way, I ended up buying a set of Dually Valves from
www.sixrobblees.com. Other than having to modify my wheel simulators a bit, I like 'em so far. Very easy to use.