A flow channel suitable for use with a peristaltic pump comprises: an upper wall having a bowed upward shape; a lower wall having one of a bowed downward shape and a flat shape; and one or more spacers between the upper wall and the lower wall disposed between lateral edges of the upper and lower walls, each spacer having a height. The upper wall, lower wall, and the one or more spacers define a lumen. When the upper wall is compressed toward the lower wall by compressing members, the one or more spacers limit vertical movement of the compressing members such that the lumen is maintained in an under-occluded condition. In some cases, the bowing of one of the upper and lower walls has a recurved shape.