Within the application of high-gradient magnetic separation (HGMS) in bioprocess engineering, peristaltic pumps are usually used for fluid transport. If the pump rotates with a constant revolution speed, the flow rate through the HGMS filter descends. This is because the free flow cross section decreases with increasing filter loading. As a result the particle loading of the HGMS filter does not occur constantly. In this work an ultrasonic flow meter was tested for the dynamic adjustment of the revolution speed, in order to stabilize the flow rate during magnetic separation.