Addressing the challenge of measuring pulsating flow

Following Titan Enterprises’ published technical paper that discussed how to mitigate the effects of variation in flow velocity, the company now offers advice on the types of flow meter systems that give the best results with pulsing flow rates, focusing on the benefits of ultrasonic flow meters.

Pulsating flow systems can be seen in process applications where the velocity profile of the flow undergoes dramatic cycling changes as compared to normal steady flow conditions. Such conditions are common in blood flow monitoring, medical, and chemical dosing systems where peristaltic or diaphragm pumps are used.

Neil Hannay, Titan’s senior R&D engineer, says: “Pulsations in a flow line are commonly caused by the pumping element: diaphragm, peristaltic, solenoid or piston pumps can all induce significant pressure and flow pulses. If this pulsation rate is not taken into account, errors in flow measurement will be seen. This can be most erroneous with electronic flowmeters as aliasing can occur.”

Few flow meters can measure these fluctuations accurately so removing the pulsations as near to the pump as possible is recommended to achieve the best results. Using advanced electronics, Titan’s Atrato and Metraflow ultrasonic flowmeters are able to accurately measure pulsating liquid flow that is less than 10Hz. To accurately measure pulsating flows above this frequency, inline pulse dampening is required to improve the effectiveness of the flow system. If it is not practical to install a damper, a length of flexible hose may reduce the undesirable effects of pulsations.

Pulsating flow is always challenging to measure accurately. However, with consideration of the system design and flowmeter performance characteristics, successful flow measurement is possible.