The valve should never be jammed in the open position.  After a valve has been fully opened, the hand wheel should be turned toward the closed position one-half turn.  Unless this is done, the hand wheel is likely to freeze in the open position, and it will be difficult to close the valve.  Many valves have been damaged in this manner.  Another reason for not leaving globe valves fully open is that it is sometimes difficult to tell if a valve is open or closed.  If a valve is jammed in the open position, the stem may be damaged or broken by someone who thinks that the valve is closed, and tries to force it open.  Valves that are exceptions to the above rule are called back seating valves.  Sometimes the operation of a back seating valve will require that it be fully opened.  Whenever this is so, special instructions to that effect will be given.  These are designed so that when fully open, the pressure being controlled cannot reach the valve stem packing, therefore eliminating possible leakage past the packing.
