Calculating flow rate through weir & plumbing advice

[Michael Hughes]

I bought a used 125 gallon tank recently with an overflow on each end that looks like this:

There are 22 weir teeth at the top totaling 2.75" of openings and the teeth are 7/8" tall. I calculated this out to 420 max gph, but wasn't sure if the teeth at the bottom are calculated the same way and just added to the total flow rate, or if the flow is slower due to traveling through the narrow channel in the overflow.

Assuming for simplicity that this doubles the flow, having two 840 gph overflows seems like a lot for a 125.

I'm planning to plumb this with a full siphon on one end along with a wet/trickle emergency drain, and on the other end have a return line and a dry emergency drain. All four holes measure 1.75".

In this case, should the wet trickle drain be situated as close to the top of the weir gaps as possible? How much further below should the full siphon be?

 

[Rocks reef]

Yes, the 'trickle' drain should be close to the top of the weirs. As far as your full siphon, you will want this about 2-3" below the trickle drain. You may need to play with how far below to make it based on how loud the water going over the weirs is.

 

[mcarroll]

I bought a used 125 gallon tank recently with an overflow on each end that looks like this:

There are 22 weir teeth at the top totaling 2.75" of openings and the teeth are 7/8" tall. I calculated this out to 420 max gph, but wasn't sure if the teeth at the bottom are calculated the same way and just added to the total flow rate, or if the flow is slower due to traveling through the narrow channel in the overflow.

Assuming for simplicity that this doubles the flow, having two 840 gph overflows seems like a lot for a 125.

I'm planning to plumb this with a full siphon on one end along with a wet/trickle emergency drain, and on the other end have a return line and a dry emergency drain. All four holes measure 1.75".

In this case, should the wet trickle drain be situated as close to the top of the weir gaps as possible? How much further below should the full siphon be?

1.75" holes translate to 1" bulkheads, right?

1" gravity drains are what the tank (almost all tanks) are spec'd for....and a 1" gravity drain is rated for 600 GPH maximum. Will run quietly at about 50% of its rating, so about 300 GPH per drain.

Trying to calculate flow through teeth seems like extra, and not sure it's even possible to calculate accurately. The teeth aren't the only inlet, so a teeth calc wold be inaccurate, maybe by 100% or more.

I know you're already on a path, but IMO consider this....

A 125 gallon tank only need about (125 x 2 =) 250 GPH to (4x) 500 GPH to be as functional as necessary. Flow at this rate can be handled by a single drain, even if one clogs up. This is how the tank was designed to run, and how I suggest using it.

Putting more flow (>500 GPH) through the sump is the only reason to do what you're considering, IMO. And there's not much reason to for that in the modern age of reefing IMO. Powerheads are king of flow. The return pump is just for feeding the sump dirty water to process....1x to 4x the display size will be enough GPH for that.

 

[Asm481]

Wouldn't using one side as siphon/drain and the other end of tank only as an emergency drain cause a fair amount of stagnant water?

 

[Michael Hughes]

Thanks for your replies and feedback! The main reason for wanting to run a full siphon was for silent operation. A couple follow up questions then:

Would you suggest running one gravity drain on each end, with an emergency drain on one side and return on the other?

My main concern with running a gravity drain is noise. Would you run each gravity drain at 50% capacity for a total flow through the sump of ~600 gph (4x system volume) or run each at 25% for ~300 gph through the sump?

Still leaning toward the full siphon - especially since it gives me two emergency drains. But definitely interested to hear your perspective.

If I go this route I might run an airstone in the unused/emergency overflow compartment just to keep the water from stagnating in there.

 

[mcarroll]

You already have enough pre-drilled holes, so it's only a matter of how you want to plumb them. Certainly there's no harm outside a few extra dollars in plumbing parts if you want to do one of the alternative drain methods in your case.

But if silence (and not more flow) is your goal (me too) then <50% is your target. They tend to start getting noisy around 50%.

If they start silent then your first sign there's an issue is drain noise – it's an excellent alert, but not if it's noisy every day. So tune your GPH down until the drains are silent. Even <2x flow is acceptable, but I'd imagine you'll get your result before the number gets that low.

At this rate you're covered – tons of margin for error. Double overflow boxes, so even if one gets destroyed completely, that tank soldiers on. Both sides have a return and both drains can handle 100% of the flow, it'll just be VERY NOISY until the situation on the other side is corrected.

The alternatives trade some risks for others, so as usual, none are "best" per se...there are always new ways to skin the proverbial cat. But IMO under normal-flow situations, the normal setup (1 drain and return per drain box) is fine for your tank. Which IMO makes sense since that's what the tank was pretty much designed for.

But I would still refer you back to my first statement...there isn't much harm in trying any of the alternatives.

 

[Dread Pirate Dave]

Thanks for your replies and feedback! The main reason for wanting to run a full siphon was for silent operation. A couple follow up questions then:

Would you suggest running one gravity drain on each end, with an emergency drain on one side and return on the other?

My main concern with running a gravity drain is noise. Would you run each gravity drain at 50% capacity for a total flow through the sump of ~600 gph (4x system volume) or run each at 25% for ~300 gph through the sump?

Still leaning toward the full siphon - especially since it gives me two emergency drains. But definitely interested to hear your perspective.

If I go this route I might run an airstone in the unused/emergency overflow compartment just to keep the water from stagnating in there.

Some have converted their durso drains to herbies.

https://www.reef2reef.com/threads/converting-durso-to-herbie-drain.963558/
Other durso threads:
https://www.reef2reef.com/search/6443894/?q=durso&o=relevance