Abstract: A crossflow filter device for filtering a pressurised feed liquid is provided. The crossflow filter device comprises: a filter membrane; a flow channel for the pressurised feed liquid which extends in a path over a retentate surface of the membrane such that the direction of flow in the channel is tangential to the retentate surface, and a filtrate derived from the feed liquid passes through the membrane leaving retentate liquid in the flow channel; and a collection chamber for the filtrate formed on an opposite, filtrate surface of the membrane. The crossflow filter device further comprises a sealed housing having a retentate side and a filtrate side which enclose therebetween the flow channel, the filter membrane and the collection chamber. The crossflow filter device further comprises, flow channel guide walls provided at an inner surface of the retentate side of the housing.