Normally-open backwater valve

A backwater valve (for preventing the flow of liquid in a reverse direction when water backs up in the valve) has a gate which sealingly engages the input opening to the valve chamber so as to prevent the flow of water out of or into the input opening. The gate is angularly moveable about a pivot point between a lower, closed position in which the input opening is closed by the gate and an upper, open position in which the input opening is open. Linked to the gate, but positioned angularly away from the gate, is a float. The float and the gate are linked such that gravity normally maintains the float in a lower position and the gate in the upper, open position but, when liquid backs up into the value, the float will float to an upper position thereby moving the gate into the lower, closed position thereby closing the input opening and preventing liquid from flowing out of the valve through the input opening.