The mechanism consists of four-bar linkage ABCD. When the level in the tank rises, liquid flows along pipe 4 into bucket 5. Lever 1, rigidly secured to the bucket, turns about fixed axis A and flap 3 is opened so that it rapidly lets out excess liquid from the tank. When bucket 5 empties, lever 1 is returned to its initial position by weight 6 which can be adjusted along the axis of lever 1 to regulate the device.
$809$LW,S$