The pressure regulating valve can basically be said to be a pressure reducing valve. The working principle of the pressure reducing valve is as follows: the high pressure medium is charged into a relatively large cavity through a small hole to realize the decompression, and actually relies on the decompression and decompression, the diaphragm or the piston. 

The two sides are out of the mouth, one side is the artificial pressure, and the valve stem that controls the size of the small hole is connected with the diaphragm (piston), so that as long as a fixed pressure is given, the pressure of the oral cavity will always be equal to this pressure. This person can be supplied by a spring or a gas source or a hydraulic source for a given pressure.