Stationary liquid flow in long (to l/d = 1250) adjacent conduits separated by a permeable membrane was studied for II and Z flow geometries and input Reynolds numbers from 2870 to 9363. The distributions of water pressure along and pressure difference between the conduits were obtained. Experimental data were compared with the numerical solution of equations derived from the momentum equation and the three-range formula for the friction coefficient. Changes in the liquid flow regimes in the conduits are taken into account; the boundary-layer Re numbers for three ranges where the friction coefficient was calculated Re < 2500, 2500 < Re < 4000, and Re > 4000 -are given.