Abstract: The combination of a storage silo and bottom unloader therefor wherein the base of the silo is formed as a hopper having a substantially central discharge outlet, the unloader being arranged to project into the silo through the discharge outlet and comprising a sweep arm pivoted for rotation in the hopper about a vertical axis disposed centrally of the discharge outlet and for vertical movement away from the surface of the hopper and means for varying the effective length of the arm comprising a mounting supporting the arm for pivotal movement about the centrally disposed vertical axis, the mounting arrangement being such that the length of the arm projecting into the silo can be altered.