yourfishman,
I agree that not every tank can easily have 1.5" plumbing used, but two or three 1" outlets equal one 1.5" pipe...so if large piping is an issue...splitting the outputs up solves that problem. Your exaqmple is a good one, as the larger a pumps gets, the better it is able to deal with the back-pressure created by an eductor.
You said that the eductors have given you good results with less than the suggested minimum of 10psi (I believe 10psi for penductors...thats why they are only 3x, and regular eductors are 5x but the suggested minimum is 12psi). I just want to point out (not for you, but for others reading this) that that means that that multiple that the eductor is able to enhance the flow by drops as well. The lower the pressure, the lower the venturi effect on the output and the less flow the eductor is able to make.
I just havent found a situation where an eductor would be considered an advantage. The wattage that they consume in the form of back-pressure just isnt made up for in the flow that they return. If the noxxle diameter is only 3/8" diameter, or .3" like you said, it would take 6 of them to come close to the same cross-sectional area as a 1" pipe, let alone a 1.5". But adding these extra outlets lowers the total pressure of the system and screws things up even more by splitting up the flow, and therefore the pressure.
Until someone changes pump technology in a big way, the low-wattage/high-flow pumps will be the best option.
And although your example is impressive, we should be sure not to confuse flow volume with velocity. Even though in the case you have shown gives an outlet with enough velocity to reach across the tank in a beam...volume is better.
That is another reason why I prefer low-head/high-flow pumps. Their relative gentle output results in a larger, although gentler water motion. Much like the difference between a Maxi-Jet and a SEIO. Sure, the MJ can project a beam of water farther, but the SEIO moves more water (comparing a MJ1200 to a SEIO 620 for instance, also note that the SEIO uses 1/3 the energy).
I dont want to get into an argument with you though. I can understand the attraction of an eductor, and was once in favor of them. Our methods may vary due to personal reasons as much as why some prefer BB or DSB.
As for the needlewheel...its a perfect example. See, a venturi skimmer (becketts, injectors, etc all operate on the same idea) uses a higher pressure pump to accelerate water in a narrow diameter section. Due to conservation of energy laws, the increase in speed results in a relative drop in pressure...sucking in air at this point. The problem is that the acceleration of the water is produced in exchange for the back-pressure that decreases the pump's capacity. A needlewheel, or reverse venturi, does not rely on back-pressure to create suction (kinda like taking two steps forward, one step back), it simply relies on the suction of the pump intake to introduce air (more like one step forward, and then another). Any time you use the creation of back-pressure for either eduction or induction, you have a net loss of flow and pressure as a result. With a needlewheel, you may still have a net loss, but its a small one because its a more direct method of introducing air as you never develop a head-pressure at all on the pump. This is why you dont see many Euro-made beckett skimmers. They simply eat too much electricity compared to a needlewheel.
yourfishman, glad to help you out with the OM site. I would have though for sure you would have seen it by now. Its a great product, with many happy customers here at RC and worldwide. As a note, Paul the owner consulted myself and a few others on hydrodynamics when a few of the users were wondering about using the OM units with eductors. I suggested that Paul not warranty/suggest the units with eductor use and gave my reasons on his website. Paul has stuck with this so far. The only exception would be if Paul changed his drum design in the future. The constant rise and drop in line pressure as the unit switches from port to port causes a cyclic wear & tear, and although there is no pre-defined tolerance for this figure...cyclic variations in pressure are the #1 reason for failure with any motor.
