Hi Steve/Paul,

The rotor on the valco valve can be replaced with a lower temperature 
rotor, which I've found eliminated sticking. I don't recall the part 
number, but the technical group at Vici should be able to help. I can get 
a part number once back in the lab (next week) if you can't track it down.

Matt Black

Environmental Sciences Research Centre
Saint Francis Xavier University
NS, Canada