https://www.pkp.de/en/pkp-products/flow/oval-wheel-nutating-disc-and-gear-wheel-flowmeters/doz07-oval-gear-flowmeter-for-high-flow-rates
DOZ07 Oval gear flowmeter for high flow rates
For particularly clear liquids or gases, the flow indicators/sight glasses are equipped with rotors, flaps or balls to make the flow visible.
oval gear flowmeterhighrates