The basic concept for the overflow is based on an article by Beananimal. The article and subsequent discussion is also posted on RC. The original document can be found here:
http://www.beananimal.com/projects/s...ow-system.aspx
I built the overflow on my existing tank exactly as the article describes including a coast to coast internal overflow. From this, I know that it works and I am confident employing it on my new tank with some modifications.
Some key points:
• Use slip bulkheads within the overflow so that standpipes can be modified with relative ease. Do not glue/weld standpipe to bulkhead.
• Limit the distance which water falls freely within the overflow. A 1/4" should be sufficient.
Here is my design as a starting point:
At this time, I haven't drilled the holes into the overflow standpipe. I am not convinced it will make any difference, but I may revisit this. The holes were intended to be drilled into the top section of the secondary standpipe and should allow the flow of water to increase gradually as the water level rises. This is the variance and is the range between which the system can be tuned.
I had originally thought to put the emergency standpipe slightly higher than the top of the overflow, but it occurred to me that this increased the risk of a return pump running dry. The display tank and sump have inversely related water levels. To raise the water level above the overflow in the main tank, the water must come out of the sump system. I settled on positioning the emergency standpipe at exactly the height of the overflow.