How to calculate return pump section size for sump

[PedroYoung]

I'm looking to build a sump out of a 120G tank and trying to figure out how much room I need in the return section. How should I determine how much volume I need there? For instance if I make it 12x8x24 (length, height, depth) I have 10G. How to know if that's enough is what I'm looking for. I might end up going external with the return, but exploring internal option.
Will be using Abyzz A200 feeding 180G display with approx 12' head.

 

[CodyRVA]

I could be wrong here, but I always thought you should build your return chamber based on the needs of the pump itself not the actual volume of the chamber. When I built my sump return chamber I sized about 3 pumps I was considering, took the measurement of the largest and built my chamber size to those specs.

 

[PedroYoung]

I could be wrong here, but I always thought you should build your return chamber based on the needs of the pump itself not the actual volume of the chamber. When I built my sump return chamber I sized about 3 pumps I was considering, took the measurement of the largest and built my chamber size to those specs.

Do you mean the physical size specs? Maybe I'm worrying about something that I don't need to but I'm imagining having too little water in the "box" the pump is sitting in to keep it full. This is a pretty powerful pump (3,800 gph with no head) and I can imagine it sucking so much water and filling the return lines and emptying the return section before getting water back to the sump via the display tank overflows (basement sump, with 12' return line). Maybe I'm crazy too (always possible) and overthinking. If pump is 8" at the widest and I make the return section 12" wide do I need to be concerned?

 

[CodyRVA]

Do you mean the physical size specs? Maybe I'm worrying about something that I don't need to but I'm imagining having too little water in the "box" the pump is sitting in to keep it full. This is a pretty powerful pump (3,800 gph with no head) and I can imagine it sucking so much water and filling the return lines and emptying the return section before getting water back to the sump via the display tank overflows (basement sump, with 12' return line). Maybe I'm crazy too (always possible) and overthinking. If pump is 8" at the widest and I make the return section 12" wide do I need to be concerned?

None of this really matters. When you first start this type of system youre going to have to add water as the return pump fires up because the return pump is going to do just that, fill your plumbing. Once the plumbing is full, the return pump only has one place to push water: the display. The display can only hold water up to your over flow. Make sense? The return pump controls it all... more or less.

And yes, the physical size. Can't have an internal return pump in a chamber thats too small and won't fit!

 

[Ryan115]

I would agree for the most part that the chamber size doesn't really matter as long as the pump fits, however there are two other considerations I like to think about for this.
This section is where the water height will change due to evaporation. The smaller the chamber, the more often your ATO will come on to make this up, or the more often that you have to add water.
I also take the opportunity to add in an extra safety measure into the system. I size this chamber based off of how much extra water I could fit into my display if the drain were to get completely blocked. On the 90g I am building right now, I figure I have ~1.25" of space above the running water line, before the tank would actually overflow. That comes out to be a little under 4.5 gallons. So if I make the return pump section that size or smaller, it potentially could offset a catastrophe caused by a snail. Granted most setup have redundant drains to prevent that as well, but $#!+ happens.
On the other hand keep in mind that the more space you take up with the return, the less space you have for everything else in the sump. Always a compromise.

 

[dowsetts101]

I think that you've all covered it nicely but when I was working out my return pump chamber size I found this article really useful in describing the needs of the pump to not slurp air and extra room for back flow from the DT when the pump is off. Some nice diagrams as well.

Hopefully it helps.

http://gmacreef.com/reef-aquarium-sump-tank-design/

 

[Rip Van Winkle]

One other thing there might be to consider is more than one return pump in the final chamber of the sump. If later on you decide to run a DR (disp. fuge) off the same sump and you want to put an additional return pump in the last chamber for the DR, the pump will displace more water. There will also be some drainage from that tank's plumbing. Just a thought.