We consider an exclusion process with finite-range interactions in the microscopic interval [0, N ]. The process is coupled with the simple symmetric exclusion processes in the intervals [−N, −1] and [N + 1, 2N ], which simulate reservoirs. We show that the empirical densities of the processes speeded up by the factor N 2 converge to solutions of parabolic partial differential equations inside the intervals [−N, −1], [0, N ], [N + 1, 2N ]. Since the total number of particles is preserved by the evolution, we obtain the Neumann boundary conditions on the external boundaries x = −N , x = 2N of the reservoirs. Finally, a system of Neumann and Dirichlet boundary conditions is derived at the interior boundaries x = 0, x = N of the reservoirs. *