A throttle valve is a valve that controls the flow of fluid by changing the throttle section or length. The throttle valve and the check valve can be combined into a one-way throttle valve by connecting them in parallel. Throttle valve and one-way throttle valve are simple flow control valves. In the hydraulic system of quantitative pump, throttle valve and relief valve are combined to form three throttling speed regulation systems, that is, inlet throttling speed regulation system, return throttling speed regulation system and bypass throttling speed regulation system. The throttle valve has no negative flow feedback function and cannot compensate for the speed instability caused by the load change, which is generally only used for occasions where the load changes little or the speed stability is not required