a peristaltic pump driven by a single speed power source has a fixed length of flexible wall tubing circumferentially positioned between the wall of the inner chamber and an adjustable band . the flexible band has one end fixed to the pump housing and the other to an adjusting screw . turning the adjusting screw varies the effective length of the adjustable band and consequently the degree of contact with the flexible wall tubing . increasing the effective length of the adjustable band flattens the tubing against the wall , thereby changing the volumetric capacity of the tubing and delivery rate of the pump . decreasing the effective length of the adjustable band has the opposite effect .