For those of us with a private well, we all have a pressure tank. It's usually tucked back in the far reaches of our basement, dusty and blue, covered in boxes and holiday ornaments. This hidden gem is used to absorb and store the water pressure that the submersible well pump delivers.
The size of this tank should be a direct correlation with the size of your well pump. If you have a 10 gallon per minute pump, your pressure tank should hold at least 10 gallons of water. Watch out though, that doesn't mean that you need a 10 gallon pressure tank! Tank manufacturers label their tanks with the TOTAL volume of the tank, not just the WATER volume. The water volume of the tank is called the Draw Down value; the amount of water drawn down before empty and the pump has to turn on. To get a tank that holds 10 gallons, look for a pressure tank thats total volume is at least 30 gallons.
Steel VS Fiberglass? Which to choose. It depends on what the tanks location is like. In a basement, crawlspace, or closet application we recommend a steel tank. We have seen longer lifespans and less failures with the steel tank giving us the confidence to install them in the majority of our applications.
If you have an extremely wet location, a fiberglass will not rust in any sort of moist environment, but they are not great handling direct sun exposure limiting their outdoor advantage.