A throttle valve is a valve that controls fluid flow by changing the throttling section or length. The throttle valve and the one-way valve can be combined into a one-way throttle valve by connecting them in parallel. The throttle valve and the one-way throttle valve are simple flow control valves. In the hydraulic system of the fixed displacement pump, the throttle valve and the relief valve cooperate to form three types of throttling and speed regulation systems, namely, the oil inlet throttle and speed regulation. system, return oil line throttling and speed regulating system and bypass throttling and speed regulating system. The throttle valve does not have a flow negative feedback function and cannot compensate for speed instability caused by load changes. It is generally only used in situations where load changes are not large or speed stability requirements are not high.