Flood Proof and 100% Silent HOB Overflow

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I made a new HOB overflow for my bowfin tank. The old one had issues when the prefilter would clog. This design eliminates all noise including that dreaded gurggling, and it also will continue to operate if the prefilter gets clogged. If the prefilter and secondary overflow pipe are both clogged, there is a third unobstructed emergency overflow pipe.

The overflow chamber is divided in two. This is in case one loses prime, and the other will continue to work. Both can handle the entire flow in case the other quits working.

The valve on the center pipe is the key to keeping this design totally silent. There is a video at the end of the pictures that shows the startup and the effects of the valve.

 

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The center pipe with the prefilter will handle most or all of the water flow. When the prefilter is clean all of the flow should go through this pipe. As the prefilter cloggs, some of the flow will begin to go down the secondary overflow.

The left pipe in this picture is the secondary overflow. The clear contraption on top holds a vent tube and the disk helps prevent the introduction of air.

The third pipe on the right is the emergency overflow. Hopefully it will never see water flow. It is there only if the other two pipes become clogged. It is slightly taller than the secondary overflow.

 

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This is about the extent of the secondary overflow. It is a piece of air line extending down the pipe. It allows water to flow in without gurgling. I have used this concept on other tanks with stand pipes and it really works well.

 

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I misfiled the pictures with the parts prior to assembly. If you would like to copy this, you'll just have to use your imagination.

The first picture is one of the ends of the overflow.

In the second picture, the left assembly is the overflow chamer(s). You can see how it is divided down the middle into two. The extra pieces of acrylic and the roll of teflon tape are there to support the pieces until the assembly is completed.

 

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Here's another view of the overflow chamber while the glue was drying.

 

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And here are the plumbing parts. The threaded fittings on the outsides were siliconed, and the center parts were glued using pvc glue.

The part numbers in the second picture are from Lowes. HD didn't have the Box Adapters (seems like they never have what you need) so I got it all from Lowes.

The reason for using the gray fittings (electrical conduit) instead of the white plumbing fittings is because plumbing fittings are tapered and conduit fittings are not. You can easily screw the gray fittings to their bottoms but plumbing fittings you can't. It is important to be able to screw these down all the way.

 

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For lack of a better name, I call this thing the "filter sled" only because it looks kinda like a sled. It keeps the filter material elevated above the drain. The legs (or runners) are important because without them water would only flow through the eggcrate above the drain.

 

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And here's a side view of the overflow so you can see how the water flows from one side to the other. (Yes, this is a picture for noobs but it has to be done. ) It will come in handy during the video.

 

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And this is the stuff I am using for the filter. Originally I sized it for an AC 150 sponge, but the dog turned it into a bunch of little AC sponges.

And yes, it says right on the front that it is treated with flame retardant. If you have any fears about it, look through my threads for the one on flame retardant.

 

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And here is the beast that this is replacing.