DIY: Tea Jar Auto Top-off

If you need a great DIY auto top off device, then you might want to look at this clever invention. The auto top off uses a Sun Tea jar, and a air tube that fills the tank automatically. How does it work? It uses water & air pressure. Originally popular back in 2005, this device still has practical application today if you need a cheap auto top off system. Follow the break below for the full how to by Greenuku.
Sun Tea Jar Auto Top-off

I promised at the beginning of the summer that I would post a how-to for a cheap gravity-fed auto top-off. Well the summer was busier than expected, and if your lazy like me, that’s a death knell to side projects (even easy ones like this). Anyway, here’s my how-to and discussion for a sun tea jar auto top-off:

What, How, and Why:
This auto top-off is gravity fed and controlled by pressure (no pumps or float switches). I don’t know if there is a good, catchy name for it, but it doesn’t seem to be a very popular type of auto top-off, even though it is arguably better than the float switch type for smallish tanks. That’s why I thought I’d post plans for a cheap, easy version.

The way this top-off works is pretty simple. The air inlet tube is placed at the level of the desired water line. The drip tube puts fresh water back into the tank. When the water level reaches the air inlet tube, the water prevents air from entering the container and the dripping stops. In practice, water is actually sucked up the air inlet tube until it rises to a level where the pressures in the container offset each other. When enough tank water evaporates, the water level drops below the air inlet tube, letting air into the container, and top-off starts again.

I’ve been using a similar top-off on my main system for about a year and have had very few problems. Here are what I see as advantages (over other auto top-offs):

• Cheap (this one cost me about $10, though fancier versions can use some expensive parts)
• Very low maintenance
• Relatively failsafe (no moving parts)
• Works (maintains your water level automatically)

Specifically, this version that I built was very cheap with (relatively) easy to find parts. (More on this later.)

Parts:

• Glass sun tea jar with plastic lid ($4 at the grocery store, a seasonal item)
• 1/4 inch (outer diameter) tubing (standard airline tubing, I got 20 feet of vinyl tubing for less than $2 at Home Depot)
• 3/8 inch (outer diameter) tubing (about $4 for 25 feet of polyethylene tubing at Home Depot)
• Number 4 rubber stopper ($1 at a chemistry supply store)
• Silicone aquarium sealant (a small tube is a few bucks [~ $3])

There are a number of reasons I went with the glass sun tea jar. For this top-off to work the container needs to be very rigid. Besides being cheap, the sun tea jar is rigid, pre-drilled at the bottom, and even comes with it’s own bulkhead (sortof). Unfortunately, sun tea jars only seem to be for sale at the beginning of summer every place I’ve been. I was going to use one a year ago, but I waited too long and they were no longer for sale.

DIY
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[*]Saw off the end of spigot so only a hole is exposed.
[*]Insert a piece of 3/8 inch tubing (a couple inches long) into the “bulkhead”. I had to shave my tubing down slightly on the end, but then it went in, providing a tight fit. This part will act as an “adapter”.
[*]Place the end of the 1/4 inch tubing into the end of the piece of 3/8 inch tubing. Mine fit snuggly. If it doesn’t, you can silicone it.
[*]Make a hole in the top of the lid for the 3/8 inch tubing. I actually hand turned a small drill bit and then used scissors to enlarge the hole. Not very fancy, but it worked.
[*]Insert the 3/8 inch tubing into the hole.
[*]Important: the whole container needs to be absolutely air-tight.
* Put silicone sealant around the 3/8 inch tubing on both sides of the lid.
* Put sealant on the hinges of the handle (on the inside of the lid).
* Put sealant on the inside rim of the lid and carefully screw onto jar.
[*]After the sealant cures (at least a day), mount the 3/8 inch tube so that its tip is at the level where water should be. Mounting can be tricky. I suggest doing something with plastic cable ties.
[*]Place the 1/4 inch tube so that it can drip into the tank. A knot in the tubing can restrict the flow to what ever rate you want.
[*]Fill sun tea jar with fresh water, put stopper firmly in fill hole in lid, and let the testing begin.
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I would suggest letting the top-off run on your “test tank” for at least a week. Any air leaks or blockages in the setup can result in a gradual change in the water level, either too low or too high.

Considerations
As I said before, sun tea jars are generally a seasonal item, so it might not be easy to find one if it isn’t summer. On my main tank I built a very similar top-off with an acrylic jar/canister that was sold as packaging for pasta. In any event, the container you use needs to be RIGID!

The reason for the 3/8 inch tubing as the air inlet, is that water will just stay in tube of smaller diameter due to surface tension, not letting the drip restart.

I have noticed that when the water level drops and air first enters the inlet tube, some tank water is sucked into the container. Over time, this leads to a lot of algae bits and such ending up in the container. If this happens, you should occasionally flush the container with fresh water, which may entail removing the drip tubing.

A more robust design would probably involve something other than a rubber stopper (my other top-off has a ball-valve), and easily deatchable tubes, for cleaning or replacement. Also you might consider using an IV dripper instead of just airline tubing for better control of the drip rate.

Note that in my pictures I was using a 1/4 inch tube as the air inlet, but I discovered that the tubing was in fact too narrow.