400X flow control valve, is a kind of high-precision pilot controls the flow of multi-function valve. Suitable for water distribution to be controlled flow and pressure pipe, maintaining a predetermined constant flow rate, the excessive flow restriction at a predetermined value, and upstream of the high pressure appropriate to reduce, even if the pressure upstream of the main valve is changed, it will not affect the downstream flow of the main valve. The valve is a change in the use of conventional throttle plate or purely mechanical principles to reduce drainage area, the use of relevant pilot valve to maximize the less energy loss in the throttling process. In case of emergency 400XA flow control valve can be completely off the flow, to avoid losses. High sensitivity control, safe, reliable, easy to debug, long service life.