The flow of peristaltic pumps is interrupted as the rollers engage and disengage from the tube. For example, considering the outlet flow, as the roller moves away from the tube it expands back from flat to its original shape. During this expansion the flow from behind the roller is partly used to fill the void. Hence flow decreases momentarily during this part of the rotation. The level of decrease depends primarily on the angle of which the rollers break away from the tube, roller diameter and outlet pressure. In some cases the flow will momentarily reverse.
If more rollers are used the frequency of the 'flow interruption' is increased giving the effect of reduced pulsation. In addition, since more rollers often means less volume between rollers, the expansion of the tube as the rollers move away is reduced in proportion to the volume available for flow.
More rollers are only recommended where needed since tube wear is significantly increased. See FAQ 'how to maximise peristaltic tube life'.