Ok, so based on everything in this thread so far I think this should be a good general formula to get anyone started with these Delevan WRW's, still lots of room for fine tuning but this should at least provide a ballpark estimate.
Pick any WRW nozzle, divide it's 20psi GPH rating in half, then divide your pumps GPH rating at about 10ft head by that, and there's your estimate.
For example my Danner/Supreme Mag-Drive#7 is a 700gph pump but at 10ft is rated 125gph since it's close to it's max pressure, it'll do 225gph at 9ft, 300 at 8ft. A WRW4 is rated about 17gph at 20psi, so half is 8.5, divide it into any of those numbers, so anywhere from 15 to 30 WRW4 nozzles should be able to run with my Danner#7. The fewer nozzles the higher pressure and finer droplets, the more nozzles the more efficient the system, but again too many nozzles and they won't function due to low pressure. There's not really any problem running fewer nozzles, just little to gain if the pump is near max pressure, for example my Mag#7 hits 0gph at 12.5ft head so fewer than a dozen WRW4's probably wouldn't result in much better spray pattern, just wasted pump potential, no harm though, most mag drive pumps have no problem running at max head so really you could run as few as desired. Hope this helps.
