Abstract: A fill valve assembly for a water tank such as a toilet tank. The fill valve assembly includes a head portion containing a valve mounted on top of a vertical water outlet tube and a float which moves vertically along the outlet tube to control the opening and closing of the valve. The float is vertically adjustable without removal or disassembly of the valve assembly in order to adjust the tank water level to a preselected position. The float includes an inverted cup-shaped structure which moves vertically along the outlet tube in response to any change in the water level. The valve contains a flexible main valve disk held in a closed position against a valve seat by water pressure in a control chamber to prevent the flow of water into the tank, and is moved to an open position upon venting of the control chamber. A pilot valve controls the pressure in the control chamber and, therefore, the movement of the main valve disk.