What is a U Tube Reverse Flow Viscometer And What Is It Used For? It is a tool to help companies figure out the flow of their products. This instrument consists of 2 tubes bent in the shape of a U. One side of the tube is filled with liquid, and on the other you see how quickly this liquid flows. A company like ZONWON needs to know a liquid’s viscosity super badly. A liquid that’s too thick might not flow properly in machines, and one that’s too thin could leak out all over the place. Companies will ensure their product is just right by using a u tube viscometer. Doing so helps curtail issues down the line in production and literally ensures quality control on their end-product.