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I have a reservior of water which feeds a vertical garden.

I want to install a type of switch/valve?? that fills the reservoir to a specific height if the water drops below a certain point (low water mark). The reasoning is if the reservoir runs dry the water pumps cooks out.

A float switch (like those used in a toilet) will not work (to my knowledge) as the water level drops and rises during the day (when the water pump comes on) but only reaches the low water mark every few weeks after some evaporation takes place. A float switch would fill the reservoir every time the water level drops, creating over flow.

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migrated from Jun 25 '12 at 7:51

This question came from our site for contractors and serious DIYers.

Why would a properly adjusted float switch add water before it reached the low water mark? – BMitch Jun 19 '12 at 14:24
check out the switches at – Bob Jun 19 '12 at 19:55
As BMitch says, a properly adjusted float switch will work. You may need one with a wide range if you want to let the tank drain down to almost empty before refilling. – user923 Jun 25 '12 at 13:34
every toilet has one of these... should be really cheap and easy using off the shelf parts to hook one of these up... of course they don't look nice – Grady Player Feb 25 '13 at 23:29

You can get a standard normally-closed ("fill up") float switch at most hardware stores or plumbing specialty stores. These usually come with a 120V plug on the end that you can plug a pump or solenoid into to be controlled by the switch, but you can cut that off and wire directly to a solenoid if that makes more sense.

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You attach this near the bottom of the tank so it can move up and down with the water level. When it's facing down, it turns on and fills the tank, and then when it faces up, it turns off. There is an amount of swing in them so the "on" and "off" levels are spread apart - this prevents small fluctuations from cycling the switch.

One easy way to attach is just using a pole made of PVC pipe (or something similar), and attaching the float near the bottom. You can leave more slack in the line depending on how much you want the tank to fill, you'll have to play with it to get the levels right. Just be careful that there is enough room for the float switch to operate without getting hung up on anything -- eg, any wires, pipes etc should be secured so they don't get tangled up.

enter image description here

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I would look at swimming pool fillers. Pool stores and catalogs offer a variety of automatic switches for filling swimming pools. These are devices you hook up to your hose, and they watch the water level, and turn on the water when it gets low. Here is a link to one I found quickly via Google, though I recommend you shop around: Pool Sentry

I would think these would work for your application, since they are designed to deal with sudden shifts in level (due to people splashing and swimming), while watching the average level to decide when to add water. But you may wish to do more investigating.

If you do decide to build something based on a toilet float, here is an example of someone building a pool filler out of one: Automatic Pool Water Filler

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here is a non electrical solution for filling water tanks

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Hi Justin, welcome to Gardening & Landscaping. Link-only posts are discouraged here -- you should post a summary of what the link is about (especially given that you're linking to a PDF). Also, per the FAQ, if you are affiliated with the site you should mention that or your post may be deleted because it looks like spam. – bstpierre Feb 26 '13 at 15:16

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