Cecil

Question for the Engineers here...

23 posts in this topic

Or heck anyone else that has an opinion. 

Option A is the way I would like to set up a small scale overflow and drain system for a future RAS tank that feeds a DIY parabolic sieve filter. Similar to the Cornell Drain I would like to set up the valves so 90 percent of the system flow is the overflow (top) and 10 percent comes from the bottom drain. I have not included the rest of the system in the drawing.

Option B is what I am seeing on page 136 in Pentair's AES 2016 catalog to feed a parabolic sieve filter. 

I don't like the extra routing in Option B, and am hoping I am not missing something going with Option A, or my Option A short circuits something due to hydraulic water pressure favoring one or the other flow. (Seems I should be able to compensate with the valves). Will Option A work? Or do you see problems and should I go with Option B? 

 

drain%20options_zpstpjmmuto.jpg

Edited by Cecil (see edit history)
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Hi Cecil

I would pipe each outlet separate in to the sieve.

IMO that would make it easyer to balance (measure) the proper flow volume from each outlet in a DIY setup.

cheers

Edited by ande (see edit history)

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12 hours ago, ande said:

Hi Cecil

I would pipe each outlet separate in to the sieve.

IMO that would make it easyer to balance (measure) the proper flow volume from each outlet in a DIY setup.

cheers

Thanks Ande,

I thought of that too. Would definitely be the safer more sure option. May just do that. 

Interestingly I have two experienced RAS people commenting on it and one says A won't work right and the other says it won't make any difference. 

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Does anyone know how far down below the water level in the fish tank the side flow of a  Cornell Duel Drain draws water? When they say mid level does that mean the mid level of the fish tank? I always assumed it was at the surface but apparently not? I see a picture in the Pentair AES catalog of the Ecotrap that make it look even below mid level. 

Does the side mount box allow the water level to stabilize by artificially bringing it up to the level if the water in the fish tank while still pulling water out below the surface? 

Edited by Cecil (see edit history)

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Not sure what you want to achieve with the dual drain.

This design is aiming at reduction of flow through solid removal filter by using 2 tank outlets. Makes no sense to me to join these again and mix. This is a way to reduce cost as solid filteration is expensive and filter efficiency is increasing with increased solid levels. Side overflow doesn't need much filteration.

Other key point in your outlet configuration is tank water level control, and I don't see that in design B.

The ecotrap is handling a bottom drain, not a side drain.

If you want to make a side drain I would put it up high, so that it will also skim the surface.

Side drains can have some other benefits such as avoiding a vortex, and reducing the teacup effect, but that isn't an issue for smaller tanks.

So far I never used dual drains like this in commercial designs because they don't collect sick/dead fish very well.

While the pentair catalog is great to have for shopping or as a reference, best tank outlets and inlets are related to tanks, tank management species etc, and that isn't covered by an of the shelf solution.

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Have just been informed that the external box that is mounted on the outside of the tank with an internal standpipe artificially raises the exit water level to facilitate drawing water below the surface of the fish tank. That is something I suspected. I think I can plumb a plastic squarish garbage can to do the same thing. A heat gun can also soften up one side so I can press it against the fish tank to fit right up against the circular tank. Then the two can be joined together with a bulkhead fitting. I will reinforce the attachment with four stainless steel bolts and a 1/2 thick piece of starboard plastic. 

I was promised a link to see the overflow in more detail. Will be happy to share it. 

Edited by Cecil (see edit history)

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I don't understand "A".  Is the upper (3-way) valve supposed to be a diverting valve or a mixing valve?  If it's a "mixing" valve, you don't need the other valve - if it's a "diverting" valve it won't do anything (useful) the way you have it drawn.

If you can find/afford a mixing valve then "A" should do what you want without the other valve; but two 2-way valves (as "B") are probably a lot cheaper?

flow.jpg

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On 10/19/2016 at 4:55 PM, phri said:

So far I never used dual drains like this in commercial designs because they don't collect sick/dead fish very well.

Phri, really quick question... What do you think the optimal water velocity (fps) should be at the bottom drain and/or dead fish inlet to effectively capture the sick/dead fish?

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On 10/19/2016 at 4:55 PM, phri said:

Not sure what you want to achieve with the dual drain.

This design is aiming at reduction of flow through solid removal filter by using 2 tank outlets. Makes no sense to me to join these again and mix. This is a way to reduce cost as solid filteration is expensive and filter efficiency is increasing with increased solid levels. Side overflow doesn't need much filteration.

I'll second this. The merit of the Cornell drain is that the solids from the bottom drain can be filtered more efficiently because they've already been concentrated somewhat, if you mix that back together with the side outlet flow, you've defeated the purpose.  My understanding is it would normally be set up something like this:

WP_20161025_001.jpg

Obviously, this is not to scale, just trying to show the logical flow sequence.

 

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Is the drawing for above or below ground tank?

Where are the solids going to after the sieve?

How are any solids from the scimmer filtered before the nitrification tank?

The Cornell drain was 1.5" dia. so, using a 3" dia would get four times the volume, 40%, how big would the scrimmer have to be to get 90% volume?

Besides why does the 2 percentages have to equal 100%?

Edited by Old Prospector (see edit history)

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7 hours ago, Old Prospector said:

Besides why does the 2 percentages have to equal 100%?

That's kind of how percentages work. With two drains, if the bottom drain is handling 10% of the effluent, then the other 90% of the effluent is going out the side drain.

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2 hours ago, MT Mind said:

That's kind of how percentages work. With two drains, if the bottom drain is handling 10% of the effluent, then the other 90% of the effluent is going out the side drain.

A scimmer on a pool, only skims the top of the surface and acts as the full point, not 90% of the exit water, unless somewhere there is a clogged line.

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13 minutes ago, Old Prospector said:

A scimmer on a pool, only skims the top of the surface and acts as the full point, not 90% of the exit water, unless somewhere there is a clogged line.

Yes, a pool skimmer will usually only handle a small percentage of the pool effluent.  If the skimmer handles 10%, then the other drains will handle the other 90%.

The Cornell dual drain design does not use a skimmer; it uses a side outlet and a bottom outlet. When the side outlet is handling 80-95% of the effluent flow, the bottom drain is handling 20-5% respectively. In order for the two drains to be handling less than 100% of the flow, there would have to be another drain added somewhere, which would be handling the remaining portion of the 100%.

I think I'm getting an idea where the "clogged line" is. ;)

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On 25/10/2016 at 5:39 AM, crsublette said:

Phri, really quick question... What do you think the optimal water velocity (fps) should be at the bottom drain and/or dead fish inlet to effectively capture the sick/dead fish?

around 0.5 m/s (1.7 fps), in addition pipe need to be big enough to handle size of fish.  

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On 26/10/2016 at 4:28 AM, MT Mind said:

I'll second this. The merit of the Cornell drain is that the solids from the bottom drain can be filtered more efficiently because they've already been concentrated somewhat, if you mix that back together with the side outlet flow, you've defeated the purpose.  My understanding is it would normally be set up something like this:

WP_20161025_001.jpg

Obviously, this is not to scale, just trying to show the logical flow sequence.

 

Yes, and seeing this, it should be clear that only a part of the water is filtered for solids, thus per definition overall water quality will be inferior compared to full stream treatment.

Something else is that I am not sure how well the parabolic screen filters can handle the concentrated solid flow, they might block up fast as the flow normally assist in pushing the solids down.   

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1 hour ago, phri said:

around 0.5 m/s (1.7 fps), in addition pipe need to be big enough to handle size of fish.  

Thanks Phri!!

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On 10/19/2016 at 4:55 PM, phri said:

Not sure what you want to achieve with the dual drain.

This design is aiming at reduction of flow through solid removal filter by using 2 tank outlets. Makes no sense to me to join these again and mix. This is a way to reduce cost as solid filteration is expensive and filter efficiency is increasing with increased solid levels. Side overflow doesn't need much filteration.

Other key point in your outlet configuration is tank water level control, and I don't see that in design B.

The ecotrap is handling a bottom drain, not a side drain.

If you want to make a side drain I would put it up high, so that it will also skim the surface.

Side drains can have some other benefits such as avoiding a vortex, and reducing the teacup effect, but that isn't an issue for smaller tanks.

So far I never used dual drains like this in commercial designs because they don't collect sick/dead fish very well.

While the pentair catalog is great to have for shopping or as a reference, best tank outlets and inlets are related to tanks, tank management species etc, and that isn't covered by an of the shelf solution.

Phri, I very much appreciate your insight.

I always liked the dual drain concept due to the reason of minimizing solid filtration costs, but this appears to come at a sacrifice of no "sick/dead fish collection".

I think the "sick/dead fish collection" would be the linchpin to possibly avoid utilizing dual drains. I will have to put the numbers in place when I am have the free time, but I think you are ultimately correct.

I sincerely wish there were more people of your caliber available to public forums, although I think I understand why there is not. Nevertheless, Thank you Phri for your patience!

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2 hours ago, phri said:

Something else is that I am not sure how well the parabolic screen filters can handle the concentrated solid flow, they might block up fast as the flow normally assist in pushing the solids down.   

It depends on the design of the flow in assisting the downward movement of the solids, plus the exit of the solids, the steeper the fall keeps the screen keeps cleaner.

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10 minutes ago, Old Prospector said:

It depends on the design of the flow in assisting the downward movement of the solids, plus the exit of the solids, the steeper the fall keeps the screen keeps cleaner.

That is exactly how I view it...

Utilizing a schedules high pressure sprayer (driven by a very cheap sprinker irrigation controller and residential water pressure) that occasionally sprays down the sieve screen...

Steep fall in the solid collection to allow the extra water from the occasional "spray downs" to push the solids to its final destination.

Belt filter...

Belt filter is what made me think of this...

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From where I got my screen filter, which was an existing AP operation, they said they used a swirl filter ahead of the screen to eliminate the majority of solids, thus less cleaning of the screen.  To me, dual outlets is more about getting the necessary flow through the tank, and just enough flow to pick up solids in bottom of the FT.  I don't get combining them ahead of the screen unless you have a ton of suspended solids.  No personal experience here though, I haven't hooked it up yet :)

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Thank you all for your comments. I screwed up the A option drawing though. The knife gate valve (Yeah I know literature says they should not be used for flow control but my experience says otherwise for my low flows) should come before the flow from the bottom drain on the horizontal axis. 

 

I'm still going to give the A option a shot but have the main flow coming out below the surface of water level of the tank. And keep in mind the sieve filter is only a primary filter and will be followed by a sand and gravel filter. 

 

Edited by Cecil (see edit history)

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On October 24, 2016 at 0:07 PM, DavidWI said:

I don't understand "A".  Is the upper (3-way) valve supposed to be a diverting valve or a mixing valve?  If it's a "mixing" valve, you don't need the other valve - if it's a "diverting" valve it won't do anything (useful) the way you have it drawn.

If you can find/afford a mixing valve then "A" should do what you want without the other valve; but two 2-way valves (as "B") are probably a lot cheaper?

flow.jpg

As I said I screwed up the drawing option A. And the valves are not  three way valves but a knife gate valves. The bottom drain does not feed into the knife gate valve. It should feed in after the knife gate valve. 

I was under the impression using the two knife gate valves would allow me to adjust the flows between the two so I can get 90/10 or 80/20 or whatever. 

Edited by Cecil (see edit history)

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18 hours ago, Old Prospector said:

Is the drawing for above or below ground tank?

Where are the solids going to after the sieve?

How are any solids from the scimmer filtered before the nitrification tank?

The Cornell drain was 1.5" dia. so, using a 3" dia would get four times the volume, 40%, how big would the scrimmer have to be to get 90% volume?

Besides why does the 2 percentages have to equal 100%?

Above ground in indoor, (tank about 150 gallons of water in the tank with 4 inches of freeboard.) 

After the sieve the solids are going into a two sock filters. Any remaining solids that are in the water stream will be polished by and sand and gravel filter.

Both solids from the scimmer [sic] and the bottom drain go to the sieve filter. However the skimmer is not actually a skimmer (drawing is a little off) but the flow will come from about a foot or more below the surface thanks to the drain box mounted to the side of the fish tank. 

Edited by Cecil (see edit history)

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