A throttle valve is a valve that controls the flow of a fluid by changing a throttle section or a throttle length. The throttle valve and the check valve are connected in parallel to form a one-way throttle valve. The throttle valve and the one-way throttle valve are simple flow control valves. In the hydraulic system of the fixed pump, the throttle valve and the relief valve cooperate to form three throttling speed control systems, that is, the throttle throttle speed regulation System, return oil throttle control system and bypass throttle speed control system. The throttle valve has no negative flow feedback function and cannot compensate for the instability caused by the load change. It is generally only used in applications where the load does not change much or the speed stability is not high.