You are making this much harder than it really is. The CSV will work with any size tank. The CSV does not let the tank fill and the pump shut off as long as you are using more than 1 GPM. Then when you turn off all the sprinklers and faucets, the CSV lets the tank fill at 1 GPM until the pump shuts off. To keep the CSV from taking 9 minutes to fill a tank that holds 9 gallons of water, you just set the CSV closer to the off setting of the pressure switch. IE; with a 40/60 pressure switch, set the CSV at 58 PSI, and it will only take 1 minute to fill the tank after you turn off all the faucets.