The present invention relates to a valve unit (100) for a chromatography apparatus, the valve unit comprising a fluid inlet (110) configured to receive an input fluid, a fluid outlet (120) configured to provide an output fluid, a first pair of fluid ports (131,132) configured to be coupled to a first column, a second pair (141,142) of fluid ports configured to be coupled to a second column, a coupling valve assembly (200) configured to direct fluid between a selection of the fluid inlet (110), the fluid outlet (120), the first pair of fluid ports (131,132) and the second pair of fluid ports (141,142) in response to one or more control signals, wherein the coupling valve assembly is configured to direct fluid using a selection of membrane valves coupled by fluid channels comprised in a body of the coupling valve assembly. The invention further relates to a chromatography apparatus comprising the valve unit and a membrane valve comprised in the valve unit.