The invention relates an adjustable stopper cum locking device for large butterfly Valves for improved sealing of valve door and valve seat comprising a first projecting plate (17) welded to lever arm (7) which rests on a spherical headed stopper screw (19) which is fixed in a second plate (20) projecting out from valve body (1) a locking bolt (23) insertable into a threaded hole (22) configured in the first projecting plate (17) of a lever to lock the lever (7) with respect to the valve body (1), the spherical headed stopper screw (19) and the locking bolt (23) in combination is enabled to push or pull the door (2) with respect to the body (1) to place the valve in an optimum sealing position, the spherical headed stopper screw (19) having holes at the opposite end for turning by a tommy bar and projectingly fixed from the valve body (1) on the second plate (20) the screw (19) is locked by a slotted ring nut (25) by inserting a rectangular steel piece (26) in the slot, wherein the locking bold head (23) comprises a spherical back to sit on a spherical washer (24) to absorb misalignment between the axis of the threaded hole (22) in the first projecting plate (17) of the lever arm (7) and the second projecting plate (20) on the body (1).
