A clamp arrangement for retaining a flexible tube (18) during operation of a roller pump (10) for pumping fluid, the clamp arrangement comprising a pair of rotatable bobbins (24A, 24B, 26A, 26B) mounted adjacent to each other. Each bobbin (24A, 24B, 26A, 26B) has a tapered groove (30), formed partially around a cylindrical surface of the bobbin (24A, 24B, 26A, 26B), and counter rotation of the bobbins (24A, 24B, 26A, 26B) clamps the tube 18 between the bobbins (24A, 24B, 26A, 26B) in the tapered grooves (30). The clamp arrangement allows tubes of different shapes and diameters to be securely held without overly deforming the tube.
