A pressure reducing valve is a valve that adjusts the inlet pressure to a desired outlet pressure, and relies on the energy of the medium itself to automatically maintain a stable outlet pressure. From the perspective of fluid mechanics, a pressure reducing valve is a throttling element with variable local resistance. By changing the throttling area, the flow velocity and kinetic energy of the fluid are altered, resulting in different pressure losses and achieving the purpose of pressure reduction. Then, relying on the adjustment of the control and regulation system, the fluctuation of the pressure behind the valve is balanced with the spring force, so that the pressure behind the valve remains constant within a certain error range.