[untamed]

Originally Posted by kwirky

What's the maximum flow through a 1.5" herbie overflow?

I've learned that this is not a simple question. The reason that it is not is that it depends greatly on the amount of head pressure above the Herbie. (that's the whole reason that Herbies work as they do)

So....the greater the difference between the height of the water above the Herbie and the height of the water in the sump....the more flow that Herbie will take. At some point, with extremely high head pressure, there would be a maximum flow...but we don't generally get near that.

In my situation, I flow about 1000 gph through each of my 2 1.5" Herbies, and they are dialed well back. That's with nearly 5 feet of head pressure.

Down below...where one sump moves into the other...there is only maybe 10" height difference from behind the Herbie to below it. That is also a 1.5" Herbie and it is running almost wide open and just barely takes that flow.

So...the upper Herbie's take that flow easily..the lower Herbie takes it just barely because there is much less pressure lower down.

Sorry, I'm sure you wanted a simpler answer.