A transfer system for controlling and initiating the flow of metered amounts of materials which may be radioactive ash, radioactive calcined salts, cement, flour, or pharmaceuticals comprising a vertical non-converging conduit which acts as a storage hopper; a stationary platform located at the downward end of the conduit to allow the radial outward flow of the material; a translatable hollow piston that acts externally but coaxially to the conduit and platform to interrupt the radial flow of material; a hopper located below the platform for accepting the material; and a housing that encloses and supports the hopper and platform and provides a dust tight seal around the apparatus of this invention.