posted 14 years ago
You can't pressurize those tanks to 40 psi. They [i]will[/i] fail. Perhaps not at first, but they will.
So, your scheme to have a second pump to pressurize the water leaving the tanks will work, it could be wired up to a pressure switch just like the one that trigger the pump to come on now. Then your well pump can be triggered on and off by the (electrical) float switch. This is problematic in several ways. You have to provide a robust float valve set to trigger the filling of the tanks, and a means of dealing with the overflow if the float valve ever fails on the on/fill/pump cycle. I would also put in a redundant (electrical) float switch, wired in series, so either switch can turn your well pump off when the tanks are full. This may also cause your pump to cycle more which shortens life.
Another method is to have the pressure tank fill with cold water (just like "normal"), then have the pressure tank fill the tempering tanks, but now you can use a literal float valve, like in a toilet to turn the water on and off. You still need the second water pump to pressuring the water leaving the tempering tanks and supplying your house. This pump runs every time you turn a tap on, and is controlled by a pressure switch in the line between the pump and the house plumbing.
Alternatively, use these tanks to catch rainwater runoff for use in your garden, a non-pressurized use, and replace them with proper water tanks that can take the pressure.
If you talk to a plumber, it is not uncommon for people to switch their water heater from gas to electric and vice versa. They might give you a couple for free over the next couple months. Strip the insulation off, and there's your pressurized water tanks. Much safer, neater and more elegant. You don't need any extra pumps and wiring and float valves and overflow piping, redundant safety switches etc.
HTH,
troy