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Overflow Sizing: Suction vs Flow Rate
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Author:  LETTUCE [ Jan 14th, '14, 09:54 ]
Post subject:  Overflow Sizing: Suction vs Flow Rate
The solids lifting overflow needs to provide suction to pull all of the solid waste from the fishtank, therefore it needs to be narrow enough diameter.

The solids lifting overflow needs to be able to transfer all volume of water coming from pressurized pump, therefore it needs to be wide enough diameter.

Diameter too small = tank overflows

Diameter too Large = solids won't lift from the bed

My personal setup has 225 GPH* (850 liters/hour) entering the tank in question.
*400 GPH (1500 liters/hour) pump at 3.5 foot head (1 meter) through a 0.75 inch outlet (19mm)

I often see discussion where people ask how large their SLO and drainage system pipe needs to be. I'd be okay with putting in 1.5" or 2.0" pipe if it weren't for the pressure needed to move the solids. Nobody seems to bring up the fact that if you go too large without enough GPH, your solids won't be attracted up the pipe. That is what is stumping me.

How do you find the right pipe size for your system with these facts in mind?
Author:  jolielaide [ Jan 14th, '14, 11:30 ]
Post subject:  Re: Overflow Sizing: Suction vs Flow Rate
This is a great question. I've only done it through trial and error, but Nate Story gives two examples on youtube.

http://www.youtube.com/watch?v=6YKcmcFyjQE

Someone also asked your same question on his blog. Yet, no response. Maybe you could post a reply with your example.

http://verticalfoodblog.com/solids-lifting-overflows-for-aquaponics/

Hope your question gets more traffic!

GOOD LUCK!
Author:  LETTUCE [ Jan 14th, '14, 11:59 ]
Post subject:  Re: Overflow Sizing: Suction vs Flow Rate
I appreciate your response, I hope others will respond and shed some light on this for me.

His SLO is a bit different from mine because he is using a standpipe with the bulkhead on the bottom of the tank. Mine will be the variety that comes from a bulkhead on the side of the tank.
Author:  Johny5 [ Jan 14th, '14, 12:10 ]
Post subject:  Re: Overflow Sizing: Suction vs Flow Rate
Hi jolielaide

I give give a few examples of what works for me.

In the fist I had a 5000L (1320G) tank. In it I ran a vertical SOL of 90mm (3.5")dia tube. It was only ever 1/3 full and I was pushing 5000L/hour (1320G/hour) through the tank.

Now I run two 2500L tanks (660G) and reduced the SOL to 50mm (1.9") as each tank has it own. These last two SOL`s cope with 2500L/hour (66G/hour) but it is about there limit.

I should have used 75mm or 90mm (3" or 3.5") pipe as that would have given me some room.

The first one 90mm
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The second version 50mm on the left. No a very good photo but it gives you the idea.
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Author:  LETTUCE [ Jan 14th, '14, 12:18 ]
Post subject:  Re: Overflow Sizing: Suction vs Flow Rate
Johny5

Would you recommend a pipe smaller than 50mm for a flow rate slower than 2500 Liter/hour (660 gallons/hour)? Mine is about 3x slower than yours at about 850 Liters/hour (225 Gallons/hour)
Author:  jolielaide [ Jan 14th, '14, 12:23 ]
Post subject:  Re: Overflow Sizing: Suction vs Flow Rate
Lettuce, That's what I use. It's a one inch elbow that comes off the side. The outer pipe is a 4-inch HDPE drain pipe. I drilled a hole in the side to fit the pvc pip through, and then, I attached an inside of the HDPE pipe.

Johny, maybe I missed it, but you are giving the interior pipe dimensions right? What are both the exterior and interior pipe sizes? Sorry, I'm just a little confused.
Author:  Tlrobb [ Jan 14th, '14, 12:24 ]
Post subject:  Re: Overflow Sizing: Suction vs Flow Rate
The system I'm setting up has 250 gph or less entering the tank and the SLO is 1 1/4" I haven't started it yet so I don't know if it will over flow but I have a valve in the design In case the flow is too much for the SLO.

I had a thought. Could a restrictor be used to increase the suction at the tip of the SLO if it it insufficient to move the solids in the tank.?
Author:  LETTUCE [ Jan 14th, '14, 12:30 ]
Post subject:  Re: Overflow Sizing: Suction vs Flow Rate
Tlrobb wrote:
I had a thought. Could a restrictor be used to increase the suction at the tip of the SLO if it it insufficient to move the solids in the tank.?


Not exactly. Take this idea to the extreme, Say you had a 1 inch tip on a 10 inch pipe. The solids would be sucked up the 1 inch section but once they hit that 10 inch potion they would not be able to continue their travel due to the decrease in pressure/velocity

Quote:
Johny, maybe I missed it, but you are giving the interior pipe dimensions right? What are both the exterior and interior pipe sizes? Sorry, I'm just a little confused.


If I understand correctly, is no interior/exterior pipe with his design. I think that his pipe (like mine) comes from a bulkhead fixed to the wall of the tank, a pipe travels down to the bottom.
Author:  Charlie [ Jan 14th, '14, 12:43 ]
Post subject:  Re: Overflow Sizing: Suction vs Flow Rate
Actually, the larger the pipe the better, 90mm is a very common size for a SLO.
Author:  tom77 [ Jan 14th, '14, 12:49 ]
Post subject:  Re: Overflow Sizing: Suction vs Flow Rate
LETTUCE wrote:
Johny5

Would you recommend a pipe smaller than 50mm for a flow rate slower than 2500 Liter/hour (660 gallons/hour)? Mine is about 3x slower than yours at about 850 Liters/hour (225 Gallons/hour)


I have 40mm SLO for 1000l/h (any more and it will start rising to my overflow) and my FT is about 1 foot above my GBs
Author:  LETTUCE [ Jan 14th, '14, 12:51 ]
Post subject:  Re: Overflow Sizing: Suction vs Flow Rate
Charlie wrote:
Actually, the larger the pipe the better, 90mm is a very common size for a SLO.


Solids would have no issue traveling across my 1.2m x 1.2m (4 foot x 4 foot) tank to get to a 90mm (3.5 inch) pipe and travel up at 225 GPH?
Author:  Tlrobb [ Jan 14th, '14, 12:52 ]
Post subject:  Re: Overflow Sizing: Suction vs Flow Rate
LETTUCE wrote:
Tlrobb wrote:
I had a thought. Could a restrictor be used to increase the suction at the tip of the SLO if it it insufficient to move the solids in the tank.?


Not exactly. Take this idea to the extreme, Say you had a 1 inch tip on a 10 inch pipe. The solids would be sucked up the 1 inch section but once they hit that 10 inch potion they would not be able to continue their travel due to the decrease in pressure/velocity



I thought that might be a possibility. But couldn't the solids eventually stack up and over flow?
Author:  Johny5 [ Jan 14th, '14, 14:14 ]
Post subject:  Re: Overflow Sizing: Suction vs Flow Rate
The 90mm pipe is storm water so the 90mm is the outside dimension of the pipe. The 50mm is sewer so the 50mm in the internal dimention.

I have used only sewer pipe in the latest build for the drains as I found a lot of algae growth on the inside of the external storm water pipes used in the first system. Sewer is a bit more expensive here but a lot stronger.

It is also a lot easier to weld as that is how I made my bulk head fittings including for the the 100mm drains.

LETTUCE

I do not see why a smaller pipe would not work for a smaller flow. But remember the smaller the pipe the easier it is to get blocked. You could try a smaller pipe if you have it then change to a larger pipe if required.

The other point is that my SOL might be only 50mm in the tank but it is joined to a 100mm drain to the RFF.

Next time I will only use a 90mm SOL just to be safe.

50mm pipe passing through the fish tank wall. the pipe runs 50% full normally but the grate needs a clean as the water is up past the SOLO. Normally it sits just short of the top of the pipe.
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The out side 50mm going into a 100mm pipe.
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A normal welded bulk head. The SOL bulk heads look terrible due to the corrugated tank sides.
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Author:  jolielaide [ Jan 14th, '14, 14:31 ]
Post subject:  Re: Overflow Sizing: Suction vs Flow Rate
Ah Johny, I was just posting on a thread about whether there is a real difference or not between bulk heads and uniseals. Those corrugated sides might be the first argument for not using uniseals. I'm not sure if it would work there. Have you tried using uniseals? That welding seems like a lot of work!

Thanks for the pictures!
Author:  Johny5 [ Jan 14th, '14, 14:46 ]
Post subject:  Re: Overflow Sizing: Suction vs Flow Rate
For the 100mm welded fitting it would take about 30 minutes to fabricate including the rubber seal and fitting.

I have it down to a fine art now. For me it is worth it as I have not had one leak or break yet. As you can see in the last photo that it is supporting the weight of the 100mm pipe and the water within.

I find that as I am a tradesman that it is better to supply pictures as I sometimes forget other people can not see what i am describing. (Nothing to do with the way I describe things of course) .

My wife is a nurse. (Avery good one at that) but she cannot see 3D images of what you describe to her without a picture or drawing. So it has become a habit to supply pictures or drawings.
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