WSS in a peristaltic pump


Wall Shear Stress Measurements in PF-6 Peristaltic Pump

An F-series Lenterra’s RealShear™ stress sensor was adapted to measure wall shear stress on the wall of plastic tube within and outside Flexicon PF6 peristaltic filling machine.

To adapt the sensor to the pump, a plastic tubing T-junction was used that shown in the figure below.  The test fluid was pumped from the tank to PF6 and returned back to the same tank via connecting plastic tubing. The pipe inside the pump was replaced with the T-junction integrated with the WSS sensor. The sensor was integrated with the T-junction tubing in such a way that its sensitive surface was flush with the plastic tubing wall when the tubing was squeezed by a roller. To accommodate the sensor within the pump, a hole was made in the bridge of the pump. The sensor was positioned vertical in all tests and was filled with liquid prior to measurements using a short tubing attached to the sensor flushing port. In this setup, where the sensor was at the center of the bridge so the rollers were passing and squeezing the tubing next to the sensor.

In another setup, the T-junction was installed into one of the connecting plastic tubes outside the pump.

WSS Raw signal: sensor within the pump


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WSS Raw signal: sensor in a tube downstream the pump


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Degradation experiments

WSS was measured for several hours while continuously pumping of protein solutions. The following data representing force pulse magnitude (FPM) evolution versus time was collected for three different protein solutions:

The ultimate result of the measurements is degradation test result – the dynamics of wall shear force after several hours of continuous pumping. Both pH4 and pH5.6 solutions displayed steady decrease of FPM after about 2.5 hours of pumping, while Sucrose PH4 solution demonstrated a temporary rise of FPM at approximately same time, followed by decay in the signal.

The degradation tests therefore separated sucrose-pH4 formulation from the pH4 and pH5.6 formulations respectively. Both pH4 and pH5.6 display similar dynamics over several hours of pump operation while the sucrose-pH4 stands apart. This conclusion is supported by the different shapes of the raw data signals for sucrose-pH4 and pH4 and pH5.6 formulations.