Abstract: Existing speed control methods for pigs are comparatively analyzed. Accordingly, a rotary bypass valve with high bypass to area ratio is designed. With the field test data available in other countries, the maximum bypass to area ratio, as an important parameter that decides the bypass valve size, is investigated. Through dynamics experiments of the adjustable-speed bypass valve, the relationships of the bypass valve opening with the bypass valve load torque and the difference of pressure front and behind the pig are obtained, which can effectively guide the selection of power components and the calculation of matched power, and provide a theoretical guidance and basis for the design and principle of the speed control device of such adjustable-speed pig.