Building Aquarium Overflow Unit

Building Aquarium Overflow Unit.

There are two primary functions that overflow unit has to serve: to supply water to a filter or a sump below the aquarium, and not let a lot of water to escape from the aquarium when the pump returning water to the aquarium stops functioning. In addition, an overflow unit should start supplying water to the system below automatically again once the pump function is restored.

The way this is achieved is by using two water chambers interconnected with a tube or a pipe filled with water. One chamber is located inside an aquarium, at the water level. It has some type of intake filter to prevent fish and other useful things from getting sucked into the chamber and filtered out of the aquarium. In it's simplest form the intake filter is just a bunch of narrow slits made in the side of the chamber. The second chamber is located outside of the aquarium, and it has an outlet located above the opening of the tube or pipe that connects the two chambers. The purpose of this chamber is to keep the interconnection pipe full even when the water level in the aquarium is low and there is no water flowing through the overflow.

Here is a page with an excellent illustrated explanation of how an overflow functions.

I made my overflow from PVC pipe. The pipe itself is fairly cheap, but the large diameter T-connectors can be quite an expense. After making one chamber using the T-connector, I figured out a way to avoid using these pieces. Here is a picture of my first overflow constructed with one large T-connector:

Materials:

4" wide PVC pipe, 1 1/2 ft
4" PVC end-caps qty. 2
90 degree 3/4" PVC adapters qty. 2
3/4" PVC pipe, 2 1/2ft
8-32 stainless steel screws 1 1/2 inch long qty. 4
8-32 stainless steel nuts qty. 4
3/4" CPVC female threaded adapter
3/4" CPVC male threaded adapter
1" vinyl tube
1" diameter clamp or a heavy-duty cable tie for securing vinyl tube
PVC/CPVC primer and glue
1 1/2 ft of 1/4" thick vinyl tube
Aquarium-safe silicone caulk. Regular caulk usually has anti-fouling agents that might be toxic to fish.

Constructing the chambers:

Cut 8-10 inch long segment of the 4" diameter PVC pipe. Draw a line around the section 1.5" away from one end. Use a saw to cut 1.5" long slits into the pipe exactly to the line drawn about every 3/4 inch:

I used my table saw to cut the slits, which makes them about 1/8" wide, but almost any type of saw should work. If your saw makes very narrow slits, make more of them.

Cut 8 inches of 3/4" PVC pipe and glue a 90 degree adapter to it:

Drill two holes for the screws through the 3/4" pipe and through one side of the 4" pipe in exactly the same places. I recommend you mark the spots on the 4" pipe first about 3" from the end with the slits and another one 1" from the other (solid) end. Drill the holes, then align the 3/4" pipe inside in such a way that the open end is about 1" inside the 4" pipe on the solid end and the end with the 90 degree adapter extends about 1" outside the sliced end of the 4" pipe. Mark the 3/4" pipe through the holes in the 4" pipe, then drill the holes through the 3/4" pipe. Screw the two pipes together and apply liberal amount of the silicone caulk to the screw threads, holes and nuts. Glue the 4" end cap to the solid end of the 4" pipe. You should get a structure that looks something like this:

The second chamber is constructed the same way, except it does not have slits, but has a 1" hole in the middle where you screw together the 3/4" male and female CPVC adapters using copious amount of silicone caulk to make it leak-proof. The 1" vinyl tube is fitted onto the CPVC adapter extending outside and secured with a clamp or a heavy-duty plastic cable tie. Insert the 1/4" vinyl tube inside the 3/4" PVC pipe and back through the 4" pipe:

Glue a 4" end cap to the bottom of the outside chamber:

The two chambers are connected using a section of 3/4" PVC pipe. The length of this pipe depends on the width of your aquarium top edge. I would recommend dry-fitting pieces together before gluing them. I painted the whole assembly using a spray-paint can. Here is how the finished piece might look like:

If you have any questions or suggestions for me, I will be happy to hear from you. Email me: denis at gerasimov dot net. Please, put "Aquarium Overflow" somewhere in the subject please.