The Actrol Model BTA — 411 Rate of Flow Control Valve prevents the excessive flow by limiting flow to a pre selected max. rate regardless of changing line pressure.
The pilot senses the differential pressure across the specially sized thin edge orifice plate mounted in the valve inlet flange. when the pressure differential is less than the set point, the main valve opens and allowing to maintain the desired flow. At the desired max. set point the pilot valve reacts to small changes in sensing pressure and controls the main valve position by modulating the pressure above the diaphragm.
When the pressure drop (across) the orifice exceeds the set point, the valve closes slightly, limiting the flow to pre-set minimum.
The orifice usually sized to generate a pressure differential of 3 to 5 psi at the desired max. flow. Adjusting the pilot setting permits the max. flow to be changed in the field above or below the original point.