How important are linear inches?

[Steve175]

. . . or is diameter more important . . . or is it how you use what you have

. . .

I'm speaking, of course, of linear inches of external overflow and diameter of drain pipes

Am mid-stage in designing a custom 450G in-wall tank (72" x 48" x 30" w/ bowfront) between livingroom and dedicated, insulated, confiscated, temp-controlled single car garage (heretofore known as the fishroom).

While water quality and flow are my paramount concern, am planning to have the fishroom be a bit of a showcase as well and, as such, cosmetically I would like the tank to be visible from 3 sides. This, however, would allow only a 32" weir for the single external overflow. Drain pipe diameter will not be an issue (can have up to 4 separate 3" bulkheads dedicated to direct overflow to sump).

A dedicated 180G refugium will drain directly into display (increasing directly total overflow) and so I would like a minimum of 3000gph overflow (ideally closer to 4000gph). The sump calculator tells me my ideal linear inches should be ~ 60" for this level of flow. Not sure whether this formula applies to this design utilizing external overflow as well. My design also incorporates a closed loop on a 4-way OM and in-tank Tunze w/ controller but 2 separate remote DSB and large skimmer will, I think, be optimized with higher sump turnover (which 270G sump containing baffles only should support well).

Fishroom will be insulated so noise is less of a concern. Large return pump (probable hammerhead) will be on manifold so exact calc is not critical. Just want opinion on whether a single 32" weir will be ball-park adequate.

If needed, I can add a second 32" weir but only if necessary due to cosmetic (and a bit of space) issues.

Taking some pics and will be starting a tank thread, but this is a loadbearing wall (involving a structural engineer) and I need to sort out this overflow issue (to dictate size of opening in wall) prior to applying for a construction permit. (I do not want to contribute to the mass of tank threads that exist for more than a year before water hits the tank).

Any and all input of this specific question is welcome.

Thanks,

Steve

 

[Untamed12]

I THINK...THINK... that you will want more linear inches of weir. This is based on wanting a relatively thin layer of water to be flowing into the overflow box.

You can certainly flow that much water over a 32" weir. It becomes a question of how thick that waterfall is and how deep the weir has to be to allow the water through.

Imagine you made only a 3" weir, and that it was only 1/2" below the top of the tank. A lot of water would pour through it, but the tank would probably overflow. If you made the same 3" weir, but 18" below the top of the tank then the tank wouldn't overflow, but you would have a wall of water coming into the overflow box and probably not get much surface removal.

That's what the linear length calculation is all about. Sure, you can compromise, but don't vary too far.

 

[Kannin]

I know that you have an external box... but, what if you added a calflow style box inside the tank, in front of your current box. Would the fact that the new box sticks out into the tank... say, 4 inches, give you more linear flow?

Also... since your fuge is raised above the tank, you could pump water from the tank, directly to the fuge. This would eliminate the need to rob your restricted flow... to feed your fuge. Or plumb a "T" into your CL before the OM... to fed the fuge. Since it is above the display... there should be no risk of flooding.