Abstract: A toilet device flush valve has a body with an inlet and an outlet and a valve seat in the body positioned therebetween. There is a movable diaphragm which closes upon the valve seat to control flow between the inlet and the outlet. A piston is attached to the movable diaphragm and there is a flow control ring mounted on the piston. The flow control ring includes water passages forming the sole flow path between the inlet and the outlet when the piston is in the open position. The passages on the flow control ring are sized to correspond to the desired flow rate through the flush valve. The passages extend in a direction to give the water flowing therethrough both axial and circumferential components to dissipate power in the water flowing through the flush valve to provide a relatively constant flow rate which is independent of the water pressure applied at the flush valve inlet.