Abstract: The flow measurement method by using differential pressure transmitter is used in hydropower stations currently. In this method, according to that the water flow in the volute casing abides by the law of constant velocity torque, combining with the Bernoulli equation and the water flow similarity law, the relation between the flow and the pressure difference can be obtained; and by processing, the flow can be calculated. The effects of differential pressure transmitter use are not ideal in many hydropower stations. Starting from the angles of experience, installation and data processing, the reasons of deviation of measured value were analyzed; and relevant solutions were given. 

Key words: differential pressure transmitter, flow measurement, volute casing, reservoir, constant velocity torque