Quote:
Originally Posted by ca1ore
I just set up a dual overflow 265 and did a 'sort of' bean animal ..... I have put a Herbie in one and a regular durso and return in the other. Herbie corner is completely silent, durso corner makes slight noise, but relatively low flow thru pipe is ok.
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Well if you really examine what is going on, you will see why it makes little sense.
Bascially, given the tank is level, or close enough, flow rate into both overflows will be roughly equal. Therefore, for the system to be anywhere near stable the flow rate needs to be set to the lowest common denominator, which in this case is the durso.
Everyone knows that dursos are not performers, or they should know anyway—otherwise folks would not be hacking stuff together to get away from them in dual overflow tanks. There is no interaction between the durso and the siphon, unless water level is above both overflows making it all one body of water; so you cannot jump the flow rate close to the capactiy of the siphon, or the durso will go nuts. Basically, it is a waste of time, and you would accomplish the same thing with dual dursos.
So have to figure (if the durso is 1.5" all the way down) a flow rate above 700 gph (combined,) but not much above or your durso would be doing more than 'making a little noise.' If you run this tank where it should be run, ~2600 gph, you will have nothing but a mess on your hands.
The "BA" system fits a very strict definition, not in the 'sort of' category. It is already hard enough to keep it clear and concise. It is these loose definitions that are causing the confusion, and giving us unsafe systems like the herbie with a trickle in the dry emergency. Many have talked about it, but I know of none that have done it the right way, in dual overflows, without bridging the overlfows, and I am not certain any have actually done that. Best solution for big tanks like this, is to ditch the overflows and start over.