Diaphragm pressure tank is mainly due to 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 carbon steel tank at the time between the nitrogen pressure in the airbag 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 Great; the second is to increase the system's entire water accommodating 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, stainless steel expansion tank pressure fluctuations play a regulatory role in the system. ???