Multi-stage restriction orifice plate is used to measure and control the limited flow and pressure drop. When the fluid flows through the orifice plate, there is a certain differential pressure producing before and after the orifice plate. For a certain aperture, the flow through the orifice plate increases with the increase of the differential pressure. However, when the differential pressure exceeds a certain value (called critical differential pressure), the flow velocity through the shrinkage of the orifice plate reaches the speed of sound. At this time, no matter how the differential pressure increases, as long as the pressure on the upstream of the orifice plate remains constant, the flow rate through the orifice plate will remain at a certain value and will not increase. Restriction orifice plate is based on this principle to limit flow and reduce pressure.