Pressure tank in the constant pressure water supply system to play a constant role in the pressure to prevent the system pressure fluctuated to reduce the frequent start of the pump can also be used to absorb the system due to valves, pumps and other open and off caused by water hammer impact, pressure The tank can be a small amount of water at night to make the main water pump system sleep to reduce electricity consumption, extend the pump life. Pressure tank in the air conditioning, to warm, solar, boilers and other closed water circulation system can be stable pressure, to avoid frequent opening of the safety valve and automatic replenishment valve frequent water and so on.