I just had a visit with Christopher and he told me about this site. I have several cold water 2 step machines which have cat 310 pumps. They have upstream injection for both the hf and caustic chemicals. Over time the heads always wash out around the check valves due to the hf acid. I have recently tried a cat 310s (which have ss inserts to seat the check valves in) and have had mixed results. I am wondering if anyone else has tried these and what there opinions are of them?