Reducing valve through the adjustment, will reduce the inlet pressure to a desired outlet pressure, energy and rely on the media itself, so that the outlet pressure to automatically maintain a stable valve. From the viewpoint of fluid mechanics, pressure reducing valve is a throttling element of a local resistance can be varied by changing the cutting area, so that the kinetic energy of the flow rate and fluid changes, resulting in different pressure loss, so as to achieve the purpose of decompression. And then rely on the control and regulation system regulation, fluctuations and the spring force of the valve after the pressure phase equilibria, so that the valve after the pressure remains constant within a certain error range. The pressure reducing valve is a specialized device to automatically reduce pipeline pressure, high water pressure in the pipeline valve before it can be reduced to the level of the valve after the piping required. The valve is widely used in high-rise buildings, urban water supply network water pressure is too high areas, mines and other occasions, in order to ensure the water supply system water point of access to appropriate pressure and flow. In view of the water loss rate and extent of waste is almost the same pressure is proportional to the size of the water supply system, therefore reducing valve to improve the system operating conditions and potential water-saving role, according to statistics, the saving effect of about 30%. Constructed type of valve past common thin film, the inner spring piston. The pressure reducing valve, the basic mechanism is to rely on the local resistance of the flow channel on the flow valve to reduce water pressure, water pressure drop range automatically adjust the import and export the water pressure by connecting the valve film or both sides of the piston. Since 2007 some new pressure reducing valve, such as fixed ratio pressure reducing valve. Given decompression principle is the use of body floating piston in the hydraulic pressure than the control, import and export of side decompression than to import and export side of the piston area is inversely proportional to. This pressure reducing valve work smoothly without vibration; the valve body spring, so spring corrosion, metal fatigue failure