I have the line coming from the RO going to the floats valve plugged into the bottom of the "solenoid" and the line going from the last particulate canister going to the RO plugged into the top of the "solenoid".
Its seems to me that when the bottom of the solenoid builds up pressure after the
float valve is closed it is supposed to push a rubber membrane up to close a small valve in the solenoid that is suppose to stop flow through the top of the solenoid. But, the problem I see with this design is that the line from the "clean" side of the RO is a lot less pressure than the mains line. It also appears That the rubber membrane is on a 1:1 ratio. I would think that that would cause the mians line pressure to override the pressure in the "clean" RO line.