Thanks both
That part number was taken from VIDA searches for that specific car profile, but the check valve doesn't show on any diagram that I would expect. The diagram it finds is for the "Exhaust emission control With air pump " which I don't have. I don't see any other diagrams.
I have a 2000 C70 which has the same valves in the same locations, and if I search VIDA for that profile, it finds the same diagram again.
Other Google trawling must have lead me to that part number, eg skandix
http://www.skandix.de/en/spare-parts...ation/1017687/
which doesn't look quite the same.
So I was hoping to get some other confirmation.
Steve