Short hydraulic lines operate mainly in the conditions of nonuniform fluid flow. The presence of grids, blades and other structures in hydraulic lines leads to a sharp change in the flow characteristics and to additional energy losses during the flow. Despite the extensive use of grids, there is insufficient information on the throughput of channels. In this article, flat plastic perforated grids of different degrees of permeability, installed at the outlet of the pipeline, have been investigated. The resistance coefficients of the grids have been determined experimentally. It has been demonstrated that the two methods for determining the resistance coefficient (by flow and by differential pressure on the grids) are identical. The influence of the grids on the capacity of the pipeline has been established. The dependence of the relative flow rate in the pipe on the surface porosity of the grids has been obtained. An alternative transition from the resistance coefficients to the filtration coefficients and permeability of the pipeline with grids has been proposed.