Years ago, a standard part of the peripheral stuff around a dentist's chair was a small round platform with a water spout over it. On it was a paper or plastic cup in a small metal holder (to give it some weight). When the cup was full, it just sat there waiting. Pick it up and there was a small squirt of water from the spout into the cup as an unseen spring pushed the platform up. When you put the empty cup back on the platform, it sank down a litle because of the weight of the metal holder and the water started. As the cup filled, the platform moved down a little more and as the water level neared the top, the water went off.
How'd they do that? It's an off-on-off valve, where "on" corresponds to platform in the middle, neither empty nor full, but there's a visible snap action to it -- the water flow starts up, doesn't change as the cup fills, then suddenly stops. The snap action is the hard part and I haven't figured it out.
I'd like to build something that works the same way, holding a gallon bucket on a hook. Hang the bucket on the hook and the water starts and fills the bucket, automatically shutting off when it's full.
I've tried searching the USPTO database but haven't had any luck, possibly because I don't know the right terms to search for. When I asked my dentist about it, he said he hadn't seen one like that for years.
Help!
Tove