New Pump - Old Working Tank - Add a Second Tank in Series?

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Our well pump failed and it cost $2,700 to replace (ouch). The technician put in a 3" 3/4HP 10 GPM Grundfos SQ10 - 290 replacing a 4" 1 1/4 HP Fairbanks Morse. The old pump and a Well-X-Trol 302 86 Gallon pressure tank were installed in 2006.

This is my first foray into understanding well systems and your help is appreciated in advance. I am uncomfortable having an old pressure tank and am exploring adding a second tank in series. The Amtrol website tank sizing tool reports a 44 gallon tank is correct for this 3/4 hp 10 GPM pump. Research indicates that a larger tank is better in general. So my tentative plan is to install a 44 gallon tank in series as a fail safe and to create a larger reservoir.

Does the new tank benefit from a pressure relief valve and drain or is it functional to do a simple t into the existing water line? I understand both tanks need to be charged at the same pressure. Other considerations?

When the old tank eventually fails would it make sense to add a second 44 gallon tank to replace the 302 to further extend system life and redundancy? If not can I leave the bad tank hooked up?

Am I overthinking this? What is the actual risk that the pump will get damaged when the old tank eventually fails if I monitor system behavior?

Thank you!!!


Cary Austin
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Lubbock, Texas
Research that recommends a larger pressure tank is over 30 years old. There are much better ways to control a pump these days and a large tank is not one of them. A pressure tanks only purpose is to limit the on/off cycles, which is what destroys pumps. When you have something like a Cycle Stop Valve to stop the cycling, you don't need a very large pressure tank. A Cycle Stop Valve and a 4.5 or 10 gallon size tank will do a better job than a room full of pressure tanks.

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