Abstract: An improved pressurized fluid check valve is provided which, when incorporated into a drill string powered by a rotary table of a drilling rig, prevents drainage of fluid from the stand pipe and rotary hose when the flow of fluid through the drill string is interrupted, such as during the attachment of another section of drill pipe to the drill string. The improved pressurized fluid check valve comprises (a) a tubular body member having a bore extensive therethrough between first and second end portions thereof, the bore having an enlarged medial portion forming a valve chamber; (b) a flow restricting assembly supported within the valve chamber of the tubular body member for selectively closing the valve chamber to fluid flow in a pressurized mode; and (c) a loading valve supported in an access bore formed through the side wall of the body member so as to communicate with the valve chamber.