The paper concerns the flow reducers which allow the flow to be self-limited as the velocity of flow increases. This kind of reducers can be successfully applied to control water flow rate from reservoirs (for example rainwater reservoirs) to watercourse (rivers, channels etc.). The concept of such device has been submitted to the Polish Patent Office and now is under patent protection. The presented construction has been tested experimentally. As a result of the construction features, a function of demanded flow parameters has been determined. During experiments, the design assumptions have been proven. The numerical simulation of the flow through the reducer was also carried out. The pressure distributions, as well as force acting on the plate of the reducer, were determined.