The drawdown of a tank is about 30% of the volume of the tank for a pressure switch setting of 30 to 50 psi. Pressure will drop more slowly with a larger tank.Originally Posted by kodiak
The drawdown should be at least eaqual to the GPM capacity of the pump for small pump (Maybe up to 1 HP) and 2 minutes for larger pumps. That means that for a small pump the actual volume of the tank should be about 3 times the GPM rating of the pump.
"Plastic" tanks are usually fiberglass reinforced plastic. The life-limiting element of most tanks is the bladder, although I have seen some painted steel tanks rust out at a weld before the bladder fails. I have never heard of a fiberglass reinforced vessel failing before the bladder fails.