A piston flow meter is a positive displacement flowmeter, which is mainly used to measure liquid flow. The piston flow meter is composed of a shell, piston mechanism, and other parts. The measured fluid fills a space with a certain volume, and these volume increments are counted and accumulated. It has the advantages of simple structure, reliable work, high accuracy, large range ratio, and little influence on viscosity. It is mostly used for measuring non-corrosive liquids, such as heavy oil or other oils, on small-diameter pipelines.