Peristaltic pumps operate using positive displacement. Fluid is forced through tubing by a number of rollers, that rotate squeezing a flexible tube against the pump housing. As the roller moves over and past a point on the tubing, it expands to allow more fluid to enter. During operation, there is at least one of the rollers in contact with the tubing at all times, therefore eliminating the need for valves to prevent backflow. The rollers or roller carriers are turned in the housing either directly by the motor or by a small gearbox that can alter the number of revolutions per minute. If the pump is directly driven, increasing or decreasing the motor speed can control the flow. Peristaltic pumps are ideal for use with corrosive and viscous fluids, as the only part of the pump to come into contact with the fluid is the tubing. With the tubing or the head being easily replaced, the pumps are relatively maintenance-free.
Thomas has 5 sizes of pumps with flows ranging from 0.1 ml/min up to 3000 ml/min. Various tube materials are available depending on their compatibility with the media being transferred. Each of the 5 sizes are available in AC or DC (DC pumps are also reversible) and are self-priming.