Waterlines, Weir Boxes, & Drain Heights (Oh My!)

iannarelli · May 14, 2024

Greeting r2r! I will get this out of the way up front, I am probably overthinking this, but I'm struggling to figure out where the waterline of the 60 gallon rimless cube I am setting up should be to make sure I don't have any overtopping or splashing while also not having a comically large gap from the top of the glass to the waterline. I know there are myriad factors that will affect the operational waterline:

Location of bottom of teeth on weir box;
GPH of return pump (coupled with) Capacity rating of overflow;
(Apparently) height of the second drain in a Bean Animal style overflow; and
Ball valve setting on primary drain
(hopefully I'm not missing any other major ones?)

I'm trying to wrap my head around the impacts all these factors have on the over geometry of locating my overflow, as I have to drill the tank. I have a Modular Marine overflow rated for 1200 GPH and my return pump is a Sicce Syncra SDC 7, which will likely run at 600 GPH MAX. According to the documentation provided by Modular Marine, at 50%-75% flow of the overflows rating, the operational waterline will be approximately 1/2" above the bottom of the teeth of the weir box. They also recommend positioning the weird box a minimum of 1/4" below the top of the glass of a rimless tank. Now for the overthinking part... I modeled the overflow in Rhino to make the follow cross-section diagram:

The current view shows the weir and overflow installed at the minimum 1/4" below the glass, which yields an operation waterline approximately 0.688" inches (DIM A) below the top of the glass. Two questions:

Is DIM A enough of a distance to not have slashes/spills from surface turbulence due to power heads/gyres and from a magnetic cleaner? What's a safe distance?
Will this be the waterline regardless of the height of the secondary drain? Now that I'm looking at this more, I assume the water level inside the weird should be BELOW the teeth, to maintain surface skimming, which means the secondary drain needs to be below the bottom of the teeth.
If I'm correct about the secondary drain needing to be below the bottom of the teeth, does is matter how far (DIM C)? Are there any advantages to having it closer or farther?

I've looked around online for answers to the first question, and responses are all over the place, typically anywhere from 3/"4 all the way up to 2", the latter of which seems like a lot. Anyway, I would appreciate any help you all can provide!

Thanks!

KStatefan · May 14, 2024

Water level in the display will be set by how much flow thru the weir.

You will want the water just barely going into the secondary and the emergency a bit higher then that. If you have "C" to big there will be noise in the overflow box.

iannarelli · May 14, 2024

KStatefan said:
Water level in the display will be set by how much flow thru the weir.

You will want the water just barely going into the secondary and the emergency a bit higher then that. If you have "C" to big there will be noise in the overflow box.

Thanks! Wouldn't the DT water level be only partially set by the flow? Globally, it would first depend on how high or low I drill to put my overflow, but then the local adjustment would be controlled by flow going into it? Or do I have it wrong?

Regarding making Dim C too big, where am I beginning the measurement from? The bottom of the teeth (as shown)? I'm struggling to see how any skimming action is going on in the weir unless the water level inside the box is lower than the DT, which would mean it would look something more like this: