Level control system for a liquid filled basin

A control system to control liquid level in an upstream basin without electrical components, the control system including the upstream basin and a midstream headloss inducing device that creates a non-linear relationship between the upstream basin's liquid level to be controlled and a lesser downstream liquid level, the control system further comprising:

• a gate at an exit of the midstream headloss inducing device, with closure means urging the gate toward closure,
• the gate being a flap gate, with a flap movable on a horizontal hinge axis, which is below the liquid level of the upstream basin,
• the closure means including a counterweight connected to the gate and urging the gate toward closure during flap travel of the gate, the counterweight being supported above the gate flap by an arm fixed to and extending generally upwardly from the gate flap such that the counterweight changes position with varying horizontal distance from the hinge of the flap as the gate opens, so that closing moment imposed by the counterweight is greatest near flap closure and becomes less as the gate opens farther, the counterweight continuing to exert closing force after the gate opens and moves toward a fully open position,
• such that the gate tends to reach a point of equilibrium of gate opening and closing forces while liquid flows out of the basin through the headloss inducing device and then through the gate, for smooth transitions of flow out of the gate,
• whereby liquid level changes in the basin are minimized, without sudden surges out the gate and without sudden closures of the gate.