What really controls the gph flow in overflox boxes ?

[HobokenAddict]

I have to ask this, even if it's been answered before, b/c I cannot find it. In overflow boxes, what is the real deciding factor in gph flow. Is it the U tube?, is it the internal box? External Box?

 

Here's why I ask. I'm going to add an overflow to my tank(already established, will not drill), and I want more than 300 max, but don't want a 600gph box on my tank, just way too much real estate in the nano.

 

Question. If I build the DIY cheap overflow using the Lee's specimen cups, what's the max gph for a 1 1/4in. ID u tube? Can I use two 3/4 inch tubes?

 

I know there are many of you out there that are much brighter than me. I appreciate your suggestions and advice.

 

Thanks

[USFnano]

There is an overflow calculator on reefcentral's main page Drain/Overflow Calc

[HobokenAddict]

So then, the U tube isn't as functional in capacity, as is the drain pipe diameter, however I don't understand what to attribute the linear overflow size to.

[gpjoe]

I think overall gravity and the size of your bulkhead would be the deciding factor in your gph. Marinedepot carries the CPR Continuous Siphon Overflow Boxes, (reading this out of my catalog) their smallest overflow box is rated for tanks up to 60 gal. with a 3/4in. bulkhead outflow and a flow rate of 300 gph. It's 6.5" wide. The 600 gph. overflow is 8" wide and uses a 1" bulkhead. Now you would assume if you use a 1" bulkhead you will get a flow rate of 600 gph. But I think it also depends on your volume, because the next size up also uses a 1" bulkhead but is 10" wide and IT has a flow rate of 800 gph. So what it boils down to is gravity and volume. Hope that helps and isn't too confusing.

[HobokenAddict]

definitely helps, thanks for the info

I've decided to diy the overflow with lees containers.

[EtOH_is_good]

i'm having a hard time wrapping my brain around this one. do you want the overflow control the gph capacity or do you want to make sure that you have spare capacity? if you build a bigger overflow then you can always use on your next bigger tank.

[HobokenAddict]

I'm going to run a mag 7 up to the tank through a scwd with about 4 feet of head. I'm going to use a ball valve to control the flow into the tank, but didn't want to have too big an overflow in my tank. I only have the 7 gal, so I don't want to take up too much room in my tank

[EtOH_is_good]

understood. im also planning a mb7. have the system running on a 10g presently. my sqwd is on the return line with an enheim 1250(?) pump and large head (similar to yours). with the sqwd and the head, the flow seems slow even for a softie tank. my suggestion is to somehow test the flow (even with a valve), since the pump is going to primarily regulate the flow. if the linear surface area and the bulkhead have excess capacity, your overflow should be large enough.

[HobokenAddict]

cool, thanks, the weldon shows up this week, so my weekend will be project full come saturday