Thx man lol was just reading up on jc's build for the 100th timehttp://www.beananimal.com/articles/hydraulics-for-the-aquarist.aspx
That's a link to a calculator beanimal has for full siphon drain rates.
For E-Drain, where there's turbulence, that's harder to answer. I'd say the top chart you posted won't work for you because it says "note: This is through an orifice, not a pipe".
so the second chart is probably what you're looking at. 2800 GPH, maybe a little more. Lots of guys here have 1.5 inch drains, somebody oughta be able to give us some "real world".
Of course, we know JC1119 ran a pair of Quiet One 6000's, and his 1.5 inch E-Drains could drain the output of 2 of those. That's 1600 GPH, 2 pumps is 3200 GPH, and he had 2 drains. Not sure about the head height, so 1400 GPH sounds about right.
There are so many factors that weigh into actual flow rate, even though I use the book "Aquatic Systems Engineering" by Escobal, I believe its a crapp shoot.
You need to factor in head height, if venturi's are used a 20% drop, and every bend, and the degree of each bend to be accurate, the math is beyond my comprehension.
That said, I use almost exclusively 1.5" drains with 2000+ gallon pumps and just throttle pumps back when necessary. Or run a Tee back to some fluidized bed reactor in the sump to compensate, which also creates more oxygenation for BB.
The venturi valve in use below creates a 20% drop in pump pressure, and flow (in theory),
but I find this changes moment to moment with environmental factors.
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Another consideration is adding a strainer to the main drain. It may slow flow a bit, but preventing larger objects getting stuck is big plus and I personally can live with that. Another consideration is if you have enough height above the second drain, it could begin to have a stronger flow if water should rise AND you have the room. I use Herbie, but I also have a third dry e-drain too. Just things to consider aside from large pipes and flow.
Yea, I have strainers on top of my 2 siphon drains. Don't want something clogging up my gate valve, that'd be a pain to get out and unclog. gotta have it.