Comment and annotated picture sent to me by email by a friend of Rossi's. I have no opinion on his comments personally, but he said:-
" Please note the output of the pumps sends fluid up about 150mm into the white header, then left, then it drops lower than the pump inlet, which will cause a negative back pressure in the header and on the outlet of the pump. The internal reactor fluid level, as shown by the sight gauge at the left of the pumps is only a cm or so above the centre of the pump.
I agree with this. The yellow horizontal lines are lined up with the water levels in the sight glasses (on the left) so they should, indeed, show the fluid levels inside the Big Frankies. Overall this means that the backpressure at the outlet of the pumps should be about 0 bar (i.e., 1 bara). I don't think that Alan Fletcher needs to copy the whole output path to duplicate the conditions seen here. A run with no backpressure at the outlet of the pump will do it.
By the way, in the picture shown the lowest Big Frankie looks like it is out of use since its sight glass seems clean and dry. Likewise, the bottom row of pumps seems completely out of use.