Normally-open backwater valve

A backwater valve, comprising:

• a liquid-retaining chamber having a top, bottom, first end, second end and two opposed sides:
• an input opening in a lower region of the first end;
• an output opening in a lower region of the second end;
• a gate positioned within the chamber and having a gate-face which sealingly closes the input opening, wherein the gate is angularly movable in a direction of angular movement about a pivot point, wherein the pivot point is positioned within the chamber, wherein the gate-face is oriented parallel to the direction of angular movement, wherein the gate is angularly movable between a lower, closed position in which the input opening is closed by the gate-face and an upper, open position in which the input opening is open, and wherein when the gate is being opened the gate moves in a first angular direction and when the gate is being closed the gate moves in a second angular direction which is opposite to the first angular direction;
• a float positioned within the chamber and not attached to the chamber, and positioned angularly away from the gate about the pivot point and angularly movable about the pivot point in the same direction of angular movement as the gate between a float upper position and a float lower position such that when the gate moves in the first angular direction the float also moves in the first angular direction and when the gate moves in the second angular direction the float also moves in the second angular direction;
• and
• wherein the float and the gate are linked such that during normal operation gravity normally maintains the float in the float lower position and the gate in the upper, open position, and wherein when there is backup of liquid in the chamber the float floats without the float being attached to the chamber and moves in the second angular direction to the float upper position and the gate is moved in the second angular direction into the lower, closed position such that the gate-face sealingly closes the input opening.