Should the rate of flow decrease the differential pressure will drop and the pilot will open causing pressure in the upper chamber to decrease. The main valve will then open to increase the rate of flow and the pressure differential and pilot setting will be maintained. The rate of flow pilot has an adjusting screw to preset the desired rate of flow and an internal needle valve to control the closing speed.
Flow Control valves can also work with hydraulic actuators (also known as hydraulic pilots). These types of valves are also known as Automatic Control Valves. The hydraulic actuators will respond to changes of pressure or flow and will open/close the valve. Automatic Control Valves do not require an external power source, meaning that the fluid pressure is enough to open and close the valve. Automatic control valves include: pressure reducing valves, flow control valves, back-pressure sustaining valves, altitude valves, and relief valves. An altitude valve controls the level of a tank. The altitude valve will remain open while the tank is not full and it will close when the tanks reaches its maximum level. The opening and closing of the valve requires no external power source (electric, pneumatic, or man power), it is done automatically, hence its name.
Flow Control Valve with an easy to read micrometer dial offers an amazing 1100 precise set points to accurately control flow of gases or liquids. The extremely high CV of the Magna Flow control valve enables very high flows for whatever media is being controlled, up to 200 PSIG pressure or full vacuum. Linear flow characteristics provide easy to set and precise metering of gases and liquids for almost any application where accurate results are required.