400X flow control valve is a multifunctional high-precision pilot-way flow control valve which is suitable for some of water distribution pipelines needing to control flow and pressure to maintain the predetermined flow and limit the excessive flow at a predetermined value. It can also reduce high upstream pressure appropriately. As a result, even if the upstream pressure of the main valve changes, the downstream flow of the main valve is not affected. The valve changes the principles that conventional throttling valve reduces drainage area purely mechanically or by the pore plate and minimize energy loss in the throttling process by using relevant pilot valves. In case of emergency, 400XA flow control valve can completely cut off the flow and avoid loss. It has high sensitivity of control, safety, reliability, easy debugging and long service life.