The 400X flow control valve is a multifunctional valve that adopts the mode of flow control employed by high-precision pilot valve. It is suitable for use in water distribution pipes within which the flow and pressure need to be controlled, and can serve to keep the preset flow constant, restrict excessive flow at a preset value and reduce the excessively high pressure upstream properly. This valve differs from other conventional throttle valve, which normally work through reducing the flow area by means of orifice plates or purely mechanically, by making use of an appropriate pilot valve to minimize the loss of energy in the course of flow regulation. The 400X flow control valve can completely stop the flow in case of an emergency to avoid loss. Accordingly, it boasts high control sensitivity and is reliable, safe, simple to debug and offers a long service life.