The pressure reducing valve is a valve that reduces the inlet pressure to a certain required outlet pressure by adjusting it, and relies on the energy of the medium itself to keep the outlet pressure stable automatically. From the fluid mechanics point of view, the pressure reducing valve is a local resistance can change the throttling element, that is, by changing the throttling area, the flow rate and the kinetic energy of the fluid change, resulting in different pressure losses, so as to achieve the purpose of decompression. Then rely on the adjustment of the control and adjustment system, so that the fluctuation of the pressure after the valve is balanced with the spring force, so that the pressure after the valve is kept constant within a certain error range.