The BURCAM 600545B 21 US gallon epoxy coated steel captive air pressure tank is designed for use with water systems assembled with a jet pump or a deep well submersible pump. The replaceable bladder is made of synthetic butyl rubber to increase reliability and lifespan. The flange is made of stainless steel and has a 1” NPT connection. There is no water to metal contact for rust-free operation. The drawdown is 7.5 US gallons (20/40 PSI) or 6 US gallons (30/50 PSI). The tank is pre-charged but the pressure should be adjusted before first use to 18 PSI for use with a 20/40 PSI pressure switch or to 28 PSI with a 30/50 pressure switch.