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I have a 58 gallon (36x18x21) that I will be back drilling for overflow and returns. My plan was to have two 3/4 inch holes for return and two for overflow. It is the over flows that I am second guessing. Does anyone think that they would not be enough and that I should go with 1 inch holes for the over flow? Right now I am planning on using a mag 7 through a scwd for the returns and if that does not seem to cut it then I may switch it to a closed loop and get a second to return from the sump. It will be near 5 ft vertical head on that pump so it may not have the flow I want. I figure that at the very least it will run enough volume to cycle water through the fuge… Anyway…advice?
"Being smart is what keeps some people from being intelligent" Thomas Sowell.
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Kelly gave some great links, my only concern is the use of the SQWD; it will reduce your flow 30-40% based on observations others have reported. What I see happening is sizing the holes for what you need now, then removing the SQWD and not having the capacity later.
Having said that, lower flow thru the sump and more flow from closed loop/streams/powerheads, as you mentioned, is the way to go. If you are going to have the tank drilled now and might do closed loop down the line, now is the time to drill the tank for closed loop as well. Even if you do not use the closed loop now, you can drop bulkheads in and cap them pipes and pipe caps...then cut the pipes later and plumb up. This is better, IMO, then breaking the tank down to redrill or having to go over the top, the extra pipes may defeat the purpose of closed loop system.
I would recomend dropping the SQWD off the return and then use it on a closed loop. This way, when you have to remove it for maintenance/repairs/..., your sump return is not offline. If needed, incorporate a plastic gate valve on the return to adjust the flow.
Myself, I am also using a Mag7 but am only figuring ~400gph after lift and head losses (see the links Kelly provided). If I put this thru a SQWD, it would endup only providing ~260gph. I will be using Tunze for the tank circulation...only because i do not have the space outside the tank for a closed loop.
Now, personally, I would drill 1" overflows for the tank...not for any numerical reason, just the minimum I would go with to feel safe...its the engineer in me. But still run the numbers on the calculators, I think hoobyists should see what recomendations are based on and how various system configurations can change flow/head loss.
Chris
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I think your numbers on the SCWD are way too liberal. SCWD lose more flow at slower rates, and less at higher rates. Marine Depot has it for sale here. If we assume a Mag Drive 7 is going to put out 400 GPH after head loss, then it'll still put out around 360 GPH after SCWD loss. Also, I have ran a SCWD for almost a year now and have NEVER had to do much in the way of maintenance on it. It doesn't get clogged up with Chaeto, etc.
However, I do agree with your ideas on increasing the size of those overflow holes. Also, putting a moderate amount of flow through your sump and more through a closed loop is really the best idea. And just for the record, you're probably best aiming for a minimum of around 20x flow per hour. So with a 58G tank, check out a minimum of a 1100-1200 GPH pump. That's really very doable.
And finally, read this article on closed loop return manifold. It is really a wonderful concept for distrubuting flow around a tank.
Paul Thompson
South Ascot, Berkshire, England
Board - West London Reef Club
Webmaster - Central Oklahoma Marine Aquarium Society
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| the picture in that link is what I need more of...I am pretty open to the concept and really like it to be honest but I am in to the astetics of the hobby very much and I like to have as little seen as possible. the trim on the tank in that picture seems much wider than any I have ever seen on a commercial tank. Now I could make mods to my tank because honestly it is a little taller than I would have really wanted at 21inches so plubing in one of those devices in has its appeal. any one have links to more applied pictures and not drawings? Also, 1 inch drain is decided...now, one or two?
"Being smart is what keeps some people from being intelligent" Thomas Sowell.
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One 1 inch drain will WORK. Two will help you out if a snail and a pile of algae (or something) gets stuck in the single drain for the overflow.
As for drains for the closed loop, you should aim for a larger, rather then smaller hole. The pumps that we use for closed loops, etc, are typically of the sort that require FLOODING with water. For instance, if you have a pump with a 1.5 inch input, do 1.5 or a 2 inch bulkhead in the tank for the manifold input. Also, I really like this bulkhead as a great choice for a very thick, solid, easy to install without breaking it or something bulkhead. And, lastly, there is a guy on ebay selling diamond hole saws at a great price. He's from Hong Kong. If you want a specific link, pm or email me.
Ok, really lastly. Here are some links to threads with nice pics of CLM.
http://reefcentral.com/forums/showthread.php?s=&threadid=757772&highlight=closed+loop+manifold
http://reefcentral.com/forums/showthread.php?s=&threadid=704391&highlight=closed+loop+manifold
http://reefcentral.com/forums/showthread.php?s=&threadid=591625&highlight=closed+loop+manifold+pictures
http://reefcentral.com/forums/showthread.php?s=&threadid=585283&highlight=closed+loop+manifold+pictures
(And Anthony, I apologize if linking to that bulkhead was inappropriate. I just have had really good luck with them and haven't found them anywhere else.)
Paul Thompson
South Ascot, Berkshire, England
Board - West London Reef Club
Webmaster - Central Oklahoma Marine Aquarium Society
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Paul, you are correct, but I think your statement is backwards; I oversimplified the numbers but lower flow leads to lower losses, higher flow leads to higher losses, principle of turbulent losses...but your numbers are more reflective of reality. I also like to think I am more conservative than liberal 
Paul has great information on the closed loop. A rule of thumb that we use in my field is that when sizing pipes, we aim for a water velocity of about 3 feet per second; this velocity yields pretty low head losses withoiut excesivly large pipes...but I find it generally equates about 1 pipe size larger than what is typically used in this hobby for similar flows, especially on short runs of pipe...so use it as a guide, then do the reality check or ask if you are unsure.
I am not familar with the bulkheads provided by Paul, but given the lower profile and softer material, I think they will give a little flex and protect the pipe/bulkhead/glass from breaking from any accidental impact. It won't have the strength of Schedule 40 PVC but then we really do not need that for our purposes, except for the more advanced/remote installations with use of ball valves on unsupported pipe.
And as far as the number of bulkeads, what do you have space for and what are you doing? I can not find in this thread so will the overflow be in the back wall up high with a long horizontal weir, as per Anthony Calfo's typical recommendations, or a more traditional setup where the hole is near the bottom and you use a tall and narrow overflow weir with a durso pipe?
If you are going with the horizontal weir near the top, than I would use two bulkhead to balace the flow as you will have little 'head' driving the bulkheads and to allow for blockage of one of the bulkheads.
If you are going with the more traditioanal setup, than you will only need one bulkhead; you won't gain much benifit from the second one and will probably have a screen on the durso to keep animals out of the stand pipe; a second durso will take a lot of real estate and require a larger weir box.
BTW, in case you did not know (some do, some do not), to figure flow velocity:
1) take the flow in gph and convert to cfs by dividing by 7.81 (yields cfh), dividing by 60 (yields cfm) and again dividing by 60 (yields cfs)
2) take the pipe diameter and square it, multiply by 3.14 (pi), divide by 4 (yields area in square inches) and then divide by 144 (yields area in square feet)
3) take the flow in cfs (step 1) and divide by the area in square feet (step 2)...this is velocity in fps
Chris
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clsanchez77 (3/1/2006)
BTW, in case you did not know (some do, some do not), to figure flow velocity.
Oh boy. The formulas are great. 
About the SCWD, what you are saying (and you do sound like you know what you are talking about) seems to contradict the numbers given on the SCWD on the MarineDepot product page, which I linked above. Do you believe those numbers are wrong? I've used 2 of them now on different tanks, but have never done any testing. It would be nice to do some flow testing with a pump and a couple of flow meters.
Paul Thompson
South Ascot, Berkshire, England
Board - West London Reef Club
Webmaster - Central Oklahoma Marine Aquarium Society
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I honeslty do not know about the flows...not having used the product. Not to derail the thread, but OM makes a two port version of their device that is a little more reliable IMO for twice the price, but then I am not using that device either; but it does not reduce the flow nearly as much.
What I do know is that in fluid dynamics, turbulent head losses are based on velocity squared, that beeing said, the higher the velocites, the higher the losses, significantly. I would imagine that the losses in the SQWD are part turbulent and part work. Losses from turbulent flow are again based on velocity squared, losses due to work are a little more complicated but are linear, negelcting effiency. Note that higher flows lead to faster switching which means the water is performing more work; lower flows yield slower current switching which is less work. Then their is efficiency, which probably increases with velocity...all a bit much to calculate...testing is the best way to go.
In the end, I still believe that higher flows will provide higher head losses, and lower flows will yield lower head losses. It just follows my understanding.
Chris
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Well, I now put my tale between my legs and stand corrected...but do note my theory was not wrong 
I just looked at the tanble SQWD & MD provided, which is here: http://www.marinedepot.com/md_viewItem.asp?idproduct=3Q1111
Work required to operate the SQWD and the efficiency relative to the water flow far more outweight the turbulent losses, so the higher the flow, the less losses in the device overall.
No dessert for me tonight 
Now having said that, I did play with some numbers...as this is what I do, and found that the headloss does increase with flow, as fluid dynamics explained previously it would. But what was interesting is that the friction coefficient reduces drastically with flow...very noticeable difference right at the 400gph mark. At 400gph and above, the head losses are about 0.2, not sure what this is similar to for perspective, maybe an open ball valve. Below 400gph, the friction coefficient ranges from 0.4-0.6, or that of an elbow. In English, efficiency is a major conponent in the operation of this device.
Now my explanation will mean little or nothing to most of us, but having see this, if I were to use this device or recommend to someone, I would recommend the flows be maintained between 400gph and 700gph for max efficiency and less wear on the pump. These flows may be higher than what is wanted for an overflow IMO, but not others...so I would then consider using this device on a closed loop and not the return pump. You could 'T' your closed loop to provide 700 to the SQWD and the remaining to a static or several static discharges, with a gate valve controlling the flow to the static head group and providing back flow on the SQWD.
This is the second time this week I was wrong in Anthony's domain! Not looking too good here!
Chris
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