The Hypercenter 2 and the early vesions of the Hypercenter XP. We havn't had 
a serious problem since Shandon upgraded the valves on our 3 XPs (at their 
own, considerable expense) The Leica doesn't appear to be prone to valve 
failure (a colleague uses one) but the same colleague had a problem when its 
vapour trap bottle became full and backed up formalin and other fluids into 
the last xylene and antemedia bottle. Routine maintenance was not being 
performed. 
I think the vapour trap exists on all enclosed processors, its worth checking 
to see if its full.
Which one do you use?


Glyn