3/4" drain enough for 120 gallon tank?

[aaliotti1]

I'm setting up a used 120 g tank with a single corner overflow. The overflow has two drilled holes (1" and 3/4"), I'm converting it to a herbie style drain and running an over the top return. My question is, will the 3/4" drain and 1" emergency drain be enough flow for the 120 gallon tank? I also have a 40 gallon sump and have not purchased a return pump yet.

 

[pdxmonkeyboy]

Yes, with full suction that 3/4 will handle PLENTY of flow..

I have 1 1/5" and a 5,000 gph pump and it handles that well. .

 

[KStatefan]

Depending on the drop height a 3/4" in full siphon will flow quite a bit. What is your target turn over rate?

 

[Pntbll687]

Here's one of the most referenced charts for flow rates

​	​	Assume Gravity to Low Pressure. About 6f/s flow velocity, also suction side of pump​	Assume Average Pressure. (20-100PSI) About 12f/s flow velocity​	Assume "High Pressure" PEAK flow. About 18f/s flow velocity*​
Sch 40 Pipe Size​	ID (range)​	OD​	GPM (with minimal pressure loss & noise)​	GPH (with minimal pressure loss & noise)​	GPM (with minimal pressure loss & noise)​	GPH (with minimal pressure loss & noise)​	GPM (with significant pressure loss & noise)​	GPH (with significant pressure loss & noise)​
1/2"	.50-.60"	.85"	7 gpm	420 gph	14 gpm	840 gph	21 gpm	1,260 gph
3/4"	.75-.85"	1.06"	11 gpm	660 gph	23 gpm	1,410 gph	36 gpm	2,160 gph
1"	1.00-1.03"	1.33"	16 gpm	960 gph	37 gpm	2,220 gph	58 gpm	3,510 gph
1.25"	1.25-1.36"	1.67"	25 gpm	1,500 gph	62 gpm	3,750 gph	100 gpm	5,940 gph

3/4in pvc will flow approximately 660gph at full siphon when using gravity. The last 4 columns show possible flow rates with pressure added, don't concern yourself with these (I just couldnt copy and paste the columns we needed without the formatting changing).

With the 3/4 drain at full siphon, you'd be looking at a turnover of around 5.5x per hour. This is in theory, in practice your flow rate is probably going to be lower due to turns in the pipe slowing things down. It will also be lower if you use a gate valve at all. I'd be guessing you'll be in in the 3-4x turnover rate.

Is this enough flow? I don't know, but with the overflow that's in the tank, even if you went with a durso pipe like it comes stock with, you'd only get marginal better flow rate. You could always get reducer bushings for the bulkhead, and use 1" or 1.5" pipe and reduce it at the bulkhead, and then use 1" pipe after the bulkhead to try and get more flow through.

I think as long as the flow is enough for the heater to maintain a constant temp in the tank, then it's enough.

 

[aaliotti1]

Depending on the drop height a 3/4" in full siphon will flow quite a bit. What is your target turn over rate?

Sorry I’m pretty new to this, what should I measure to get the exact drop height ? I don’t have a target turn over rate, I guess more on the low side as BRS said a 3-5 times was plenty.

 

[Pntbll687]

Sorry I’m pretty new to this, what should I measure to get the exact drop height ? I don’t have a target turn over rate, I guess more on the low side as BRS said a 3-5 times was plenty.

Drop Height would be from the top of the drain pipe to where it connects to the sump. You're probably somewhere around 30"-36" if it's on a typical premade stand you can buy from a store. The drop height can really add to the total gph especially when someone is plumbing a sump in a basement and you have 12+ feet of height the water will be travelling.

Just plumb the tank with a full siphon 3/4" pvc and the 1" emergency. Get a return pump thats controllable, probably a max of 2000gph if you wanted to run a manifold off of it as well. Get the water flowing and as close to where you want it with just adjusting the return pump. Use a gate valve on the full siphon drain to really dial in the overflow so it's super quiet.

 

[slojim]

measure display tank water level to sump water level
also, just because you have a 3/4" hole, doesn't mean you can't adapt immediately to 1" pipe if you want to go up a size. I don't suspect that's necessary.

 

[slojim]

sorry - corner overflow - I missed that - so if you corner overlfow level is below your display tank level, use that as your starting height like Pntbll687 said

 

[Pntbll687]

sorry - corner overflow - I missed that - so if you corner overlfow level is below your display tank level, use that as your starting height like Pntbll687 said

I just went from the top of the full siphon drain pipe, to the sump. I'd measure it the same if it were a overflow box on the back of the tank.

But I don't think OP needs to worry about drop height or get lost in the minutia of drop height adding X amount of gph when the result is going to be the same. He's going to end up with somewhere in the range of 600-900gph draining into the sump using the corner overflow.

 

[aaliotti1]

Here's one of the most referenced charts for flow rates

​	​	Assume Gravity to Low Pressure. About 6f/s flow velocity, also suction side of pump​	Assume Average Pressure. (20-100PSI) About 12f/s flow velocity​	Assume "High Pressure" PEAK flow. About 18f/s flow velocity*​
Sch 40 Pipe Size​	ID (range)​	OD​	GPM (with minimal pressure loss & noise)​	GPH (with minimal pressure loss & noise)​	GPM (with minimal pressure loss & noise)​	GPH (with minimal pressure loss & noise)​	GPM (with significant pressure loss & noise)​	GPH (with significant pressure loss & noise)​
1/2"	.50-.60"	.85"	7 gpm	420 gph	14 gpm	840 gph	21 gpm	1,260 gph
3/4"	.75-.85"	1.06"	11 gpm	660 gph	23 gpm	1,410 gph	36 gpm	2,160 gph
1"	1.00-1.03"	1.33"	16 gpm	960 gph	37 gpm	2,220 gph	58 gpm	3,510 gph
1.25"	1.25-1.36"	1.67"	25 gpm	1,500 gph	62 gpm	3,750 gph	100 gpm	5,940 gph

3/4in pvc will flow approximately 660gph at full siphon when using gravity. The last 4 columns show possible flow rates with pressure added, don't concern yourself with these (I just couldnt copy and paste the columns we needed without the formatting changing).

With the 3/4 drain at full siphon, you'd be looking at a turnover of around 5.5x per hour. This is in theory, in practice your flow rate is probably going to be lower due to turns in the pipe slowing things down. It will also be lower if you use a gate valve at all. I'd be guessing you'll be in in the 3-4x turnover rate.

Is this enough flow? I don't know, but with the overflow that's in the tank, even if you went with a durso pipe like it comes stock with, you'd only get marginal better flow rate. You could always get reducer bushings for the bulkhead, and use 1" or 1.5" pipe and reduce it at the bulkhead, and then use 1" pipe after the bulkhead to try and get more flow through.

I think as long as the flow is enough for the heater to maintain a constant temp in the tank, then it's enough.

I did not think of that, So how much more flow should I be able to get by using 1” pipe and just reducing it at the bulkhead?

 

[Pntbll687]

I did not think of that, So how much more flow should I be able to get by using 1” pipe and just reducing it at the bulkhead?

Maybe 10-15% more, nothing crazy.

I would honestly stick with straight 3/4" inch and make life easier on yourself. Don't get tied down with some of these numbers and how to get more flow through a bulkhead. The only flow that really matters is can your return pump match the flow through the drain pipe. Buy a dc return pump that goes up to about 1500gph and you'll have more than enough flow

 

[aaliotti1]

Maybe 10-15% more, nothing crazy.

I would honestly stick with straight 3/4" inch and make life easier on yourself. Don't get tied down with some of these numbers and how to get more flow through a bulkhead. The only flow that really matters is can your return pump match the flow through the drain pipe. Buy a dc return pump that goes up to about 1500gph and you'll have more than enough flow

Thanks, I told myself I would keep it simple haha.

 

[outhouse]

3/4 will handle all you can throw at it while still being quiet.

You dont need that much flow for a 120, I ran a 100 with a single 3/4 drain durso, for over a deacde and it was dead silent.

anywhere from 200-500 gph all you need with a small sump like that