Pressure tank is mainly composed of the valve cover, inflatable mouth, air bags, steel tanks, flanges composition, when it is connected to the water system, the main function as a storage device, and when the water pressure is greater than the expansion tank steel tank body between the nitrogen pressure in the airbag, the system will squeeze into the water system under the action of pressure within the expansion tank balloon, so that one will be compressed nitrogen gas tank between the balloon, its volume decreases, the pressure increases; Second, the entire water system will increase the accommodation space, the system pressure is reduced until the system water pressure and body to reach a new equilibrium between the nitrogen pressure in the airbag did not stop the water. When the system water pressure is less than the gas pressure in the expansion tank, water balloon will be in the tank on the balloon between nitrogen pressure extrusion, fill back to the system, the system volume decreases water pressure increases, the bladder tank between nitrogen volume increases pressure drops, until both reach a new equilibrium, the water stops flowing from the airbag squeeze back into the system, the pressure tank to play the role of regulating the system pressure fluctuation. Structure is as follows: tank between the airbag is factory pre-charge of nitrogen tank outside the paint layer, inlet and outlet connected directly to the system with a tee or metal hose, exhaust valve interface can be promptly removed from the system and balloon The water overflow air valve can also be directly related to the death in order to avoid overflow of water from the top, the dust cap is below inflation / deflation port, add nitrogen or release the portion of the gas.