So this project has been stuck in my head for a while and I had to put it down on "paper" to get it all out.
Special thanks to Scott Bennett for inspiring this (without the inspiration I might have had a good nights sleep
Also thanks to Brassman for turning me on to the single point level float switches
Attached is the drawing that I came up with. The overall objective is to keep this really simple.
I am always using CLR to remove the deposits caused by the water to keep it working
Cliff - I think you make a good point about the solenoid clogging up from the deposits and not working correctly. I have 2 filters inline that will hopefully help reduce this problem.
The basic operation is turning on the switch inside the coach which closes the autofill circuit. The float valve is NC (Normally Closed) so that when the tank is less than full the circuit is powered and causes the solenoid to open and fill up the tank. When the tank is full the float valve then opens the circuit and turns off the solenoid.
Some additions that I would like to add to this are -
1. A light that comes on in the coach when the tank is full (could probably use tank indicator lights but a simple light indicating that the autofill circuit is open is what I am thinking here)
2. A moisture/spill indicator in the overflow tube that powers a circuit with an alarm to let you know that water is flowing through the overflow tubes.
Because my coach is 12v I will keep all things electrical 12v as well. You could changes the parts/pieces to fit your coach.
I think I could pull this off for less than 100$. I have seen 1/2" 12v solenoids for less than 30$ on amazon. The single point valve fromt he gems website is $35 or so and I am sure that I could find one cheaper. The relay and switch would be about 10-12 bucks and the wire would cost about 20$ unless I have some lying around somewhere.
I have a 3/4" FPT opening and a 1.5" FPT opening on the top of my freshwater tank. My Idea is to have the 1/2" pex line feed into the 1.5" opening along with the connection to stick a hose in to fill up as well. The 3/4" opening would be where I would screw in the float switch. They look pretty small on paper and I think I would have no problem fabricating something that would just screw into the top of the tank.
This project is a ways off for us but when I get to it I will post my success failures on our website and here as well.
If anyone else wants to get a head start on me take lots of pics and let us know how you do.