we are using the FZ6 pressure regulator. the only difference is the plastics are from the R6 (also the pump) but i'm assuming it's the same pump since the id number on the pump was the same. we just had to bore a new hole in the r6 plastics to be able to use the "old" fz6 pressure regulator, and now everything is fine
However. The R6 pump is a lot more quiet than my FZ6 pump. the fz6 pump was much more noisy. is there any reasonable explanation to why my fz6 pump was so noisy ?