Abstract: A pipeline detector is driven by the pressure of the medium in pipelines to detect pipeline defects. In order to ensure its detection accuracy, its running speed shall be controlled lower than 5 m/s, but the flowing speed of the medium in gas pipelines is too high. In this paper, it was proposed to control the running speed of detectors by equipping speed control devices. After the operating principles of speed control devices were introduced, two types of speed control devices (i.e., fan blade type and conical cylindrical type) were developed. Both of them can control the running speed of detectors by changing the area of the discharge channels. The speed signals from the odometer wheel is real-time compared with the speed range preset by the control program and the speed control devices are driven by motors to control the real-time running speed of detectors in the preset range. It is shown from test and industrial application that these speed control devices can run normally in actual working conditions.