A bladder tank is a type of hot water tank that includes a flexible rubber bladder that fills with water. The bladder uses the difference between the air and water pressure to act as a mechanical water pump.
A hot water tank that uses a bladder is usually effective at keeping water pressure and temperature at a steady rate even when multiple fixtures are operating within the home. A bladder tank usually includes a specialized valve that prevents water from flowing out without sufficient pressure. When water pressure is greater than the air pressure inside the tank, water collects in the bladder. When the water pressure weakens, the air pressure in the tank pushes the water out.