Once the pump is sized for your home, then we must size the pressure tank to your pump. It is best to have the pump operate at least one minute before it shuts down. Tank draw-down should not be confused with total gallons of the tank.
Most pressure tanks have a bladder in them that separates the air from the water, allowing less water needed to be in the tank. A 35 gallon bladder type pressure tank has a draw-down of 12 gallons. The draw-down of the tank should be close to the GPM of the pump, to allow for at least a minute of pump run time.
The pressure tank has nothing to do with how much pressure the pump puts out, but is merely a holding vessel for your water. Without a pressure tank there would be no room for the air to compress, and the pump would rapidly turn on and off causing the system to short cycle. Short cycling is the leading cause for pump failure.
At Kellner, LLC, we proudly install Flex-Lite fiberglass pressure tanks. The Flex-Lite FL series' improved CAD2 diaphragm design is stronger and won't crease and wear out like bag designs. Flex-Lite well tanks features a chlorine resistant 100% butyl diaphragm with a precision molded copolymer polypropylene lower water chamber for superior air and water separation. This patented design allows each size tank to have a properly sized water chamber, matched to the drawdown performance of that tank. When it comes to performance and durability, the CAD2 system cannot be beat. Flex-Lite tanks come with a 5 year warranty.