Okay, let me narrow things down here. Ive modded many pumps into streams and needlewheel/meshwheels, and have a good deal of insight into making these pumps by now.
Important factors for NW pumps:
-volute, or impeller shroud diameter and thickness. this is where most of the actual mixing & bubble chopping happens for a NW, not at the NW/meshwheel.
-intake and output diameter. A NW pump by default becomes a low-pressure pump, so many high head pumps, with their smaller inlets and outlets and higher speed impellers (to generate and conserve centrifugal force/pressure)... can actually be outdone by smaller low-pressure pumps that have larger intakes and outlets.
Thats why I want to narrow things down a bit here... a 500gph pump is still pretty wide range. The new ATI/Tunze needlewheels are only 40w pumps, yet pull 1000 lph! thanks to their large shrouds and output/intake diameters.
-impeller diameter, thickness, speed: speed plays the most important role... but in reverse... too much speed works against you. Yet another reason why low-pressure (as in low speed) pumps can work better than high-pressure ones, the faster pumps can be so fast that that disk of foam or disk or needles which replaces the impeller of the pump gets spun so fast that to the water and air... its pretty much just a spinning solid disk of plastic... not alot of 'bite' left to actually move any water.
-intake venturi. Actually, not that important as many people think. See, with venturis and mazzeis (and becketts), the more velocity you can achieve within the venturi, the more air gets introduced. Not so with Needlewheels. There is a threshold of air intake which is not determined by the venturi, but rather by the pump itself. See, on a beckett, the more air that the beckett doesnt change anything for the pump itself, as its 'downstream', but with a needlwheel, if the velocity of the intake venturi increases to the point where there is more air being taken in than the pump can actually mix, the pump chokes. The best venturi is actually nothing more than a valve on the intake, with the air line introduced right after the valve. This way, you can adjust the water pressure... restricting the water to the point where the most air gets taken in, but not so much that the pump cant draw in enough water to continue to actually move that mixture.
Maybe there is some detail in the above that will help you... otherwise your best bet is to post some pics of your attempts..
What pump were you trying to convert exactly? 500gph? What... a mag5? I suppose I should have been more specific, as there are 500gph pumps out there that are 25 watts, and others that are 55 watts, and the wattage has more to do with the pump's potential as a NW than the pump's gph rating. There are some pumps in that class that can pull 1000lph or more (red dragon, tunze, etc) and others that can only do 500lph. So please post pics, or tell us what pump you are trying to convert... thats a good place to start... have to make sure the pump is a good candidate.
and 2) increases water velocity by decreasing open flow.
