Air-driven auto-topoff Mark II

Even though willtell beat me to it, I've just finished half of my system. I'm still waiting for two float switches from floatswitches.net (sorry Physh1, couldn't resist the price), but the main components are finished.

 

I started off with a Flip'n'Fresh from ShopKo. This has a cool flip-top that I thought would make filling up the resevoir easier. I also chose it because it was tall and skinny, thus fitting behind my 2.5g mini-bow perfectly. However, there is a design consideration. As the water level in the resevoir lowers, it will be more difficult for the air pump to push the water up farther and farther into the main tank. Therefore, always test your system with a nearly empty resevoir to make sure your pump can handle the strain. By using a short, fat resevoir you reduce this problem.

I drilled two holes with a 5/32" bit, slightly smaller than rigid airline tubing. Then I forced the tubing in (snug fit) and sealed them with a thick rim of super glue gel. I think I should have used silicone though, because the super glue is brittle and I think the seal will break easily. Fortunately, this design is tolerant of a little air leakage -- a completely airtight container is not necessary.

While the design is tolerant of an imperfectly airtight resevoir, the flip lid leaked so much air I only got 2" of head with three airpumps ganged together. If you bought these things to store food in, forget it, they are NOT anywhere close to being airtight.

 

So, regrettably, I had to silicone the flip lid shut. The whole lid assembly still unscrews though. The threads are pretty airtight. But, filling the resevoir will be less convenient. In a bit, I'll get to why I think I wasted $4 on this stupid container because a gallon milk jug would have worked just as well.

The bottom line is the air input. It's short. The other, the water output, goes to the bottom of the container and the rigid airline tubing is angle-cut so it has a nice wide opening.

Here's the magic. An air bleed-off valve.

 

The Flip-n-Fresh is not solidly rigid. That means that when the air pump comes on, the container exands with air pressure. Then the water starts flowing.

 

Without this valve, when the pump shut off, residual pressure would continue to drive another 6oz of water into the tank. Bad. Other air-powered topoffs require a rigid resevoir to prevent this problem. But by opening this valve a little bit, when the pump shuts off, the water flow stops immediately and the excess pressure hisses out through the valve.

 

You must adjust it though, 'cause if you open it too much, the air pump cannot get enough pressure into the resevoir to pump water out. Tweaking was pretty easy though, and tolerant of a bit of maladjustment. I just turned closed the valve, turned the pump on, waited for the water flow, and then slowly opened the valve until the water flow slowed. Turn off the pump -- water stops with only a few extra drops.

 

That's why I think a plastic milk jug would work too, even though they expand and contract a lot with the pressure.

 

With a relatively airtight resevoir, I got suprisingly good head with my cheapo airpump. More than 3 feet, and while I didn't bother to grab more tubing to see how high I could get the water was still flowing at a good clip, so I bet you could go from under a stand into the main tank.

 

Costs:

Float switch w/ shipping: $9

Electrical cord for float switch: $1 (dollar store)

Airpump: $6

Tubing, tees, and valves: $4

Resevoir: $4

 

Total: $24

nice

Looks like it turned out wellB)

 

Cameron

If you got your floatswitch from floatswitches.net can you show me how you wired it. I've been trying to follow willtell's setup but i don't know how to wire this switch.

Still waiting for the switches to arrive... hope they get here soon! I'll post some wiring pics to this thread they do.

My float switches arrived 10 days after I sent the money order off to David @ floatswitches.net.

 

First step was to stop by my LFS and buy one of their used "catch cups" for $4. This one is made by Lee's and is the kind that hangs on the side of the tank. It's seen better days.

 

I used #16 Weldon and some scrap acrylic to make mounting flanges.

 

This whole thing is ugly as sin, but since it's all going out of sight behind the tank, I don't care. Too much. :|

Here I've mounted the two switches to the carrier plate. Again, scrap acrylic laying around from when I did my lights.

Now I grabbed a $1 extension cord from the dollar store. Using a hobby knife I verrrry carefully split the two wires without exposing the wire.

I cut the hot wire and stripped the ends. The neutral stays intact. The hot wire is the small blade, the neutral is the broad blade. Sometimes one side or the other will be identified with a stripe or with ribbing.

 

It's very important to cut the hot side. It standard electrical practice to switch with the hot line, never with the neutral, for safety reasons.

Here's a diagram. My setup was a little more complicated because I used two switches. Why? Safety. If a float switch ever got stuck in the 'on' position, it would dump a gallon of freshwater into my tank, killing everything and making a nasty mess of my desk at work. This way, even if one switch sticks on, the other will prevent over-topoff.

 

The bad side is if just one switch sticks in the 'off' position, no topoff will happen in spite of the other switch still working. I'd rather that happen, though, than the alternative.

 

The switches are wired in series.

...and here's a pic of the same thing. Take one wire from each switch -- doesn't matter which -- and tie them together with a small wire nut. Then take the two remaining wires and tie one to each side of the extension cord with medium nuts -- doesn't matter which way. There's no polarity here.

Another trip to Radio Schmack. This was their smallest "Project Box".

This holds the wire joints so they are not exposed. I wrapped things in electrical tape, just to be safe. I had to Dremel out an opening for the wires. I also drilled a hole in the back of the box so I can mount this on the wall (next to my CF ballasts). Didn't want to lay this on my desk -- it would short out if water got spilled on it. It's a lot safer mounted on the wall.

Here's the finished project. I used nylon license plate bolts and nuts to mount the carrier plate to the flanges. These will allow me to adjust the water level in the tank by screwing the carrier plate up or down.

 

What's left? Plug the airpump into the extension cord, plug the extension cord into the wall, and make a couple of siphons from the Lee's catch cup into the tank, so the water level in the tank is communicated to the switches.

 

The bad news is work has tightened their anti-camera policies. I work in an R&D test lab and I guess they don't want pics of the latest prototypes walking out the door. So, sorry I won't be able to show the thing in action.

I wonder if you could find a jumbo peanut butter jar or spagetti sauce jar made of glass so that you could stop worrying about container expansion? Have a nice meal for ten and you get your resevoir for free. I got the same float switches. Works like a dream. I put mine right in the tank, but I like the HOB with siphon idea better.

I wonder if you could find a jumbo peanut butter jar or spagetti sauce jar made of glass

Actually, I got a glass cookie jar with a plastic lid first. But it was only 1/2 a gallon, and I wanted more capacity. A gallon should last me at least 10 days for those really long vacations -- such as Christmas break.

great thread, youve answered my question of not having to look at the float switches in the main tank but...

 

I am the first to admit Im a little punchy so I dont understand how you are planning to transfer water back and forth from the HOB that the switches are located in.

 

could I touble you for a diagram?

 

I like the pretty pictures ???

Well, I had visions of using the U tube from a Penguin or something, but I ended up bending some U tubes out of rigid airline tubing with a flame. I used two cause they're awfully narrow, slowing water exchange. And besides, one little bubble would cause topoffs to stop.

 

I have the topoff output going into the HOB. If I piped the output into the tank and I ever lost those two siphons, I would dump a gallon of FW into the tank with predictable results. But, plumbing the topoff into the HOB causes some interesting effects. To wit:

 

The first few days running, specific gravity in the tank gets a little too high. That's because the water coming in from the HOB is almost the same SG as the tank. During this time I take water from the main tank and throw it away, triggering more topoff and bringing the SG down to normal.

 

Eventually, the water in the HOB becomes fresh enough that things balance out and the SG in the main tank stays normal. In a sense, I'm topping off with brackish water. But osmosis moving salt back into the HOB balances this out, so things stabilize after a few days of SG fluctuations. Just keep an eye on your SG for the first week or so and adjust as required.

 

WARNING -- be sure to break the siphons when doing a water change!! Otherwise, all that brackish water from the HOB goes pouring into the tank... not... good...! Uh, don't ask me how I know that.

 

Another interesting effect is the topoff kicks in whenever I take a water sample to test SG -- the float switches are sensitive enough to detect the small amount of water it takes to fill my SeaTest hydrometer.