Living in Sulawesi, Indonesia I'm in the planning stage for an approximate 300 gallon square aquarium with a square overflow in the center of the tank. I settled on the style so that all sides can be viewed and can be set up differently with plants and open space. It will also give a full 2 meters length of weir hopefully keeping the "waterfall" noise down.
I am able to use a very large semi in-ground tiled concrete and glass external sump with plumbing running under the floor inside. I would run fans on the sump to keep the water temperature down here in the tropics and I can set up an automatic water level system running well water into the sump.
I've decided to use the BeanAnimal's Bar and Grill - Silent and Fail-Safe Overflow System
style overflow plumbing for quiet operation and fail safe peace of mind when I am away at work. The image below shows the basic layout of the tank and plumbing.
The tank is 1.5 meters square with the overflow 50 centimeters square. The overflow is 55 centimeters deep while the outer tank has 60 centimeter high panels. The three 1 1/2 inch standpipes form the Bean Animal overflow while there are two 3/4 inlets splitting into a total of four 1/2 inch bulkheads. The tank side of the inlet bulkheads will be fitted with Loc-Line inlets so that they can be individually directed for flow.
The above image shows the layout of the standpipes. The one on the right is the full siphon with the one on the left acting as the open channel while the one in the middle is the emergency drain in case of blockage. I plan to set the water level in the overflow so that the open channel runs about half full provided that the flow is quiet at that level. That will be about 1 1/2 inches down from the top of the weir. It would be nice to run it a little higher so that the water flow over the weir into the overflow might be laminar and noiseless but I'm not sure how high I could safely go. I might just have to buy some extra pipe and male adapters and experiment a bit.
All of the standpipes will use the flat pancake style of strainer to keep out fish and to minimize any vortex action which would introduce air into the siphon and create noise.
The full siphon is set a bit lower than the open channel so that it has more chance to start a siphon before the water level goes too far over the top of the toothless weir. The lower level of this means that if there is a power outage the water in the overflow will drop a little more but my sump will be larger in capacity than the tank so no problem there. Once the water reaches the height of the weir the open channel breather tube will be shut so that it can form a full siphon and the emergency is just barely higher than the weir.
The problem is that I have never used this type of overflow set-up before and nobody else has a write-up on the web showing anything like my planned build.
If anybody can see any dumb mistakes in the design please let me know
so that I can make alterations in the design before ordering all of the equipment as a lot of this stuff needs to be imported.