1/2" Return lines?

twistedfinn967 · Oct 6, 2020

Okay, I'm looking to replace my current small leak 120 gal with a new one. Looked at SCA Aquariums and I like it. The back glass comes pre-drilled for two 1/2" return lines. Is it just me or does that seem too small? My current setup is 1" over the top so that is why I'm wondering.

fishguy242 · Oct 7, 2020

hi,jmo i would expect 3/4 on a standard 120

mfinn · Oct 7, 2020

I do agree it seems small for a 120 gallon tank, I would think that a 1" return line split into two 1/2" lines would be fine.

nereefpat · Oct 7, 2020

mfinn said:
I do agree it seems small for a 120 gallon tank, I would think that a 1" return line split into two 1/2" lines would be fine.

Those are my exact thoughts. Seems a little small, but will be fine. I would use a 1" return from your pump, then a 1" tee, then reduce each line to the 1/2" after the tee.

twistedfinn967 · Oct 7, 2020

Thanks for the replies. Glad it wasn't just me.

92Miata · Oct 7, 2020

Remember that dynamic head is largely about friction - and you lose way less flow pushing through a 1/2" bulkhead than you do pushing through a run of 1/2" pipe.

twistedfinn967 · Oct 7, 2020

92Miata said:
Remember that dynamic head is largely about friction - and you lose way less flow pushing through a 1/2" bulkhead than you do pushing through a run of 1/2" pipe.

So should I run the 1" as far as I can to each return hole and then choke it down to 1/2" at the last minute? What about adding a valve to even out the flow since it will be a much shorter run to one return than the other?

DCR · Oct 7, 2020

Two 1/2" lines are not equal to one 1" line in terms of flow. It is cross-sectional area rather than diameter so you would need roughly 4 of them to equal one 1" line just on an equivalent fluid velocity basis. Even then the frictional loss is greater with 1/2" at the same fluid velocity so it is more like five 1/2" lines being equal to a 1". I think you are going to be very restricted with only two 1/2" ports - probably to something like 300-400 gph total depending on the pump you select . I would definitely swage down at the bulkhead and might consider going over the top.

fishguy242 · Oct 7, 2020

agree reduce at bulk

92Miata · Oct 7, 2020

DCR said:
Two 1/2" lines are not equal to one 1" line in terms of flow. It is cross-sectional area rather than diameter so you would need roughly 4 of them to equal one 1" line just on an equivalent fluid velocity basis. Even then the frictional loss is greater with 1/2" at the same fluid velocity so it is more like five 1/2" lines being equal to a 1". I think you are going to be very restricted with only two 1/2" ports - probably to something like 300-400 gph total depending on the pump you select . I would definitely swage down at the bulkhead and might consider going over the top.

The ports make very little difference because the head loss is proportional to the length - and the bulkheads are very short. I run 3/4" lines to eductors that have probably a 1/4" orifice. They still move plenty of water.

Do they affect things - yeah. A lot, no.

Yes, run 1" up to the bulkheads, if you need valves to even things , make sure they're 1" (or even 1 1/4) - because the valves are narrower than a normal section of pipe.