Pressure tanks are used in closed water circulation systems to balance water flow and pressure, avoiding frequent opening of safety valves and frequent replenishment of automatic water valves. The expansion tank not only serves to accommodate the expansion water, but also serves as a makeup water tank. The expansion tank is filled with air and can obtain a larger volume to accommodate the expansion water. High and low pressure expansion tanks can use their own pressure to supplement water to the pressure stabilization system in parallel. The control of each point of this device is interlocking reaction, automatic operation, small pressure fluctuation range, safe and reliable, energy-saving, and good economic effect.