Abstract: The invention provides a toilet cistern dual flush valve (10) operable selectively in a full flush mode in which a relatively large volume of water is discharged from the cistern or a partial flush mode in which a relatively small volume of water is discharged from the cistern. The dual flush valve (10) comprises a stem (36) carrying a valve closure (38) seatable on an outlet from the cistern, means to raise the stem (70, 72,74), buoyant means (50) attached to the stem (36) which in the full flush mode maintains the stem (36) in the open position until the relatively large volume of water has been discharged and the buoyant means (50) loses buoyancy whereafter the stem (36) descends under gravity to the closed position, and means (54) which operates in the partial flush mode to add sufficient mass to the stem when the relatively small volume of water has been discharged causing the stem (36) to descend to the closed position.