A sintered coupling ring is described, comprising a ring of coupling teeth which comprise relieved flanks extending from wedge-shaped end faces and, on the side opposite the wedge-shaped end faces, a stop that protrudes radially beyond the tooth tip. In addition, the present invention provides methods of delivering a nucleic acid to a cell using the AAV4 vectors and particles. When the valve is opened for initial entry of gas into the exchanger, the gas flows about the free edge of the valve. The block time generator provides a block time based on the load representative signal.