Don't want to buy an expensive float valve?
Make your own!
I have been building a hydroponics garden, and I wanted to make sure my reservoir doesn't run dry and destroy my pump (or kill my plants), but a side entry float valve would have cost me $30+ at the local hardware store, and I had already spent my budget on pipes and plants.
So, calling on my childhood obsession over MacGyver, I looked for what I had lying around, and built a cheap and surprisingly effective float valve! (effectively for free!)
Step 1: Disassemble
If you look at the spray end, you should notice it looks like an inverse nut.
Push your pliers into the corners, and turn like a screw, it isn't hard to get undone.
When you have the front off, unscrew the small plastic nut from the other end, and slide out the innards.
Step 2: Mod and Reassemble
That is the one thing holding us back (it is way to stiff, and we don't need it!).
Simply slide it off.
Now, without the spring, there is nothing holding the plastic shaft to the handle, the shaft will happily go in to the open position, as the nut is pushed up by the handle, but it won't push back in.
I found a small rubber thing (picture 2) laying around, so I drilled a hole in the centre, and used a grinding bit on my dremel like tool to make it shorter.
This fit perfectly on the shaft before the handle (it actually 'screwed' on!).
Now when the handle goes down, it pushes on this bit of rubber and the shaft goes in as expected.
Step 3: Add the Weight / Float
The rest of the wire should be wrapped around the neck of a water bottle.
Put enough water in the bottle to pull down the handle, leaving enough air to push the handle up via buoyancy.
Now just attach your contraption to your larger water barrel, drop the float into your reservoir, firmly attach the sprayer and you are done!
When the water level drops, so will the bottle, pulling the handle down.
When there is enough water in the reservoir, the bottle will float, pushing the handle up, and closing the sprayer.