DIY auto top off

[EricB]

Heres what I was thinking for a really cheap auto top off.

basically an upside down 2 liter bottle of fresh water, with a ping pong ball to keep the fresh water from mixing with the saltwater.

Is there an better really cheap way to do it than this?

[EricB]

Now that I think about it, I probably don't want a rubber gasket in the water, so I'd probably use something else for that.

[fishfreek]

off the top of my head I dont think yo would have much sucess given that the water current might just push the pingpong ball off the tubing.

You can make up a topoff that is graveity feed if you use one of those toilet bowl floats.

[jsoong]

I agree that this probably won't work. The ping pong ball won't generate enough upward force to seal the bottle. If I remember my physics correctly, the force is the weight of the water displaced by the ball, and that is far less than the weight of the water in the bottle.

I do have an auto-topup in my humidifier in my forced air furnace. It works something like this:

[center:df3d24e3b3] water supply === L__________ o ___[float]

shut off ......... fucrum[/center:df3d24e3b3]

Basically the fucrum & lever magnify the force of the float (which is rather large for the 1/4" supply line) to shut off the water.

You can duplicate this, or simplier yet, go to home depot & buy the float repair kit for a few bucks. (I have to change this assembly every 1 or 2 years due to hard water deposits!)

The 2 liter bottle will work fine without the ping pong ball. The water would not flow out of the 2 liter bottle until the tube received air from the surface of the water... When the water is released from the 2 liter and water covers the tube, the flow will stop until the next time the water level drops... Much in the same way a 5 gallon drinking water cooler works... or the self watering dog/cat bowls..

[EricB]

don't forget that the tip of the tube extends under the water, so you actually have negative air pressure holding up all of the weight. The ping pong ball would only be in there to prevent mixing fresh water with the salt water.

The ping pong ball would only be in there to prevent mixing fresh water with the salt water.

Huh? You are supposed to mix the fresh water with the saltwater. That is the whole point of topping off...

The gravity auto top off isn't rocket science..It is science though,, used to do the same things in junior high. The water creates a vaccum in the bottle and therefore will not come out of the tube unless the water level gets below it... I just like to keep it simple. The ping pong ball is merely over kill...

[jsoong]

Oh I am so embarassed ... I forgot about the negative suction in the bottle.

It is lucky to see all these experts around here to correct sloppy thinging on my part.

[BillyZ]

Huh? You are supposed to mix the fresh water with the saltwater. That is the whole point of topping off...

I believe his concern is the water pre-mixing while it is still in the bottle. Because of the difference in [acronym:18b2bfe34c="Specific gravity"]sg[/acronym:18b2bfe34c], the salt in the water in the tank will diffuse up into the bottle, and lower the overall [acronym:18b2bfe34c="Specific gravity"]sg[/acronym:18b2bfe34c] in the tank system, which is not what you want. The ping pong ball will help prevent the pre-mixing problem. I think your theory will work just fine as long as the cage is narrow enough to keep the ball from being pushed sideways. I wouldn't worry about a gasket as long as the lip of the bottle is relatively smooth.

[BillyZ]

also, I presume this is a relatively small system? as 2 liters of auto-top off will only really work for a rather small tank. I think my 55 probably goes through 2 liters of evap every other day.