Above: ill. 1 (a) The U-tube portion of a Coriolis mass flow meter. All fluid flow will travel through the U-tube portion of the flow meter. (b) This diagram shows the U-tube vibrating up and down. The up-and-down movement is caused by a magnet. (c) This diagram shows an end view of the U-tube. When fluid is flowing through the U-tube as it vibrates, the tube will tend to flex.