An ultrasonic flowmeter for liquids measures flow using transit time technology. It sends ultrasonic signals upstream and downstream through the liquid. By comparing the travel times of these signals, the meter accurately calculates the flow rate.

Transit time flowmeters offer high accuracy, non intrusive installation, and suitability for many liquids with varying viscosities and temperatures. They can also measure flow in both directions.

Their accuracy can decrease in very turbulent flows or liquids with air bubbles or solids. They also have a higher initial cost, though low maintenance often balances this over time.

Overall, transit time ultrasonic flowmeters provide precise, reliable, and versatile liquid flow measurement in closed pipe systems.