Butterfly valves shall be installed such that the rotation of the valve is in the same direction as the flow stream, when closing. When a butterfly valve is installed in a pipe line, spacer rings shall be installed if the adjoining pipe bore is likely to obstruct the movement of the disc or if the process requires a smooth internal diameter transition between the pipe and the valve. Removable spools may be required at butterfly valves to enable removal in the event of a jammed open disc.