water rises.....
ok,
when I installed the damn things way back when,
if you had an array of them tied in together, you wanted the water to pass slowly up through the panels
you basically have a parallell type of system that you have set up through the panel..or panels.....filling up the bottom one inch copper manifold, then disperseing up through the 3/8 tubes....YOU WANT IT TO RISE EVENLY
the water comes in on the bottom on the left and goes out on the top on the right.....
if you put the fluid it through the panel too quickley, the water or glycol will simply find the quickest path through the panel... wether it be the first two or three tubes , bypassing and ignoreing the other tubes going up the panel.... it is takeing or finding the quickest route through the panel...
(just like in a parallel water heater layout, if anything gets out of wack, it draws much more off one and not the other)
Pressure is not really an issue, but the volume you are passing through the panel will determine how much heat you collect and also how efficient the panel is,,,,
we used to actually install these glass flow meters in the lines to the panels which could be throttled down with ball valves. to the right gpm.......
does that make any sense,
......it has to rise like bread , slowly and evenly
if you were to buy a real set of panels
it would tell you the proper GPM for max effect....
look around at panels for sale and see what they advise