This valve uses a high accuracy pilot operated flow control and is suitable for flow and pressure pipeline control to keep the preset flow unchanged.1imit an extra—big flow at a preset value and properly lower the high pressure on the upstream.the flow at the downstream will not be affected even if the pres-sure of the main valve at the upstream varies.1t changes the principle for a throttle valve to reduce the basin area purely mechanically or by way of using orifices and utilizes the related pilot valve to reduce the energy loss during throttling to the utmost extent and features sensitive control,safety,reliability,easy debugging and long duration