Abstract: A pilot-operated ball cock valve of the type wherein a vent to a pressure chamber is controlled by a lever arm to thereby control the flow of fluid through the valve. A movable rod is slidable in aligned relief and pilot conduit openings and has a valve sealing element carried on the rod. The valve sealing element is adapted to seal off the relief opening in one position of the rod and to open the relief opening in another position of the rod. Further, the sealing element is adapted to close off the pilot conduit between the pressure chamber and the inlet opening when the rod is in the other position. The valve is advantageously formed in two pieces which screw together through a threaded core. The float on the arm has a hole in an outer portion thereof and is rotatably mounted on the arm to adjust the buoyancy of the float and thereby adjust the height to which the arm will rise in the tank.