Peristaltic Pumps in Metering Applications and How They Compare to Other Metering Technologies
Peristaltic pumps are positive displacement pumps, typically used to pump sterile and aggressive fluids that should not be contaminated during the pumping process. This pump works on the same principle as peristalsis, a natural phenomenon observed in living organisms - such as the esophagus of humans. The pump consists of a number of shoes (typically two) that compress flexible tubing along the circumference of a round pump casing. In the case of peristaltic pumps with two shoes, the distance between the rotary shoes is constant. This invariable distance between the two shoes generate the same amount of vacuum for suction regardless of the rpm of the motor that rotates the shoes. The quantity of fluid encapsulated in the subsequent phase of vacuum generation is proportional to the vacuum generated. Thus, the flow rates of peristaltic pumps are precise over three sequential constrictions of the tube. The consistent nature of the pump’s output flow rate makes it viable for metering and dosing applications.
Factors affecting flow rate:
Though the output per cycle of the pump is indifferent to the rpm of the motor, the flow rate is, however, directly proportional to the rpm of the motor. Variations in the rpm of the motor produces relevant change in the output flow rate, which can be demonstrated by assembling a variable frequency drive (VFD) in the peristaltic pump system. The rpm of the motor needs to be constant after the required flow rate is achieved, since metering applications require an invariable flow rate over a long period of time.
Metering application and performance characteristics:
Peristaltic pumps are widely used as metering pumps in the medical field due to isolation of fluids during pumping. Accuracy of peristaltic pumps’ flow rates ranges between ±0.25% and ±5%. Primarily these pumps are used for infusion of medicinal fluids because of their ability to infuse at a rate as low as 0.1 ml/hour. Such slow infusions can prevent blood clots in the vein. Sensitive administrations like these require pressure guards to avoid infusion of air caused by the lack of source fluid. An optical device is used for detecting bubbles introduced in the system during the pumping action. The pump’s working mechanism incorporates an anti-siphoning mechanism and thereby makes them suitable for medical metering applications. Apart from metering applications that require a constant flow rate, known-volume metering applications can also be served by peristaltic pumps. Known-volume metering is also known as dosing. Dosing applications requiring both constant flow rate and constant volume per dosage, use peristaltic pumps with rpm regulators and pinch valves. These pumps calculate the volume by extrapolating flow rate and time. Certain applications require only accurate dosage of the fluid and are catered by peristaltic pumps that lack rpm regulators. The volumetric output of pumps lacking rpm regulators is calculated by deducing the number of rotations and output volume per three occlusions. The number of rotations or the number of occlusions is calculated by using an angular measurement device.
Comparative analysis of metering pumps:
Peristaltic pumps operate without any moving parts or environment in contact with the fluid; this gives them an advantage over other metering pumps in medical and pharmaceutical applications. This advantage is restricted within applications requiring fluid isolation. Other metering pumps such as a diaphragm pump offer better chemical and physical compatibility. The pressure handling capabilities of the diaphragm pump significantly eclipses the pressure handling capabilities of peristaltic pumps. Solenoid operated metering pumps offer better accuracy over peristaltic pumps and their ability to be operated by conventional 4-20 mA allows industrial compatibility. Peristaltic pump users incur significantly lower maintenance costs when compared with other metering pumps. Metering applications determine the choice of pumps and therefore all types of metering pumps have distinctive market penetration.






