A flow cell unit to be docked against a flat lid surface to form a closed flow cell arrangement, the flow cell unit comprising a top surface with protruding walls of elastic material defining three or more adjacent elongated flow channels, each flow channel comprises a first fluid port and a second fluid port, wherein the walls separating adjacent flow channels comprises a valve section of reduced height, thereby allowing selective opening and closing of a flow path transverse to the elongated flow channels by controlling the docking force between flow cell and the lid surface to an open docking state and a closed docking state respectively.