Stuffing box and blow out preventing device for polish rods of oil well pumping units

In a stuffing box which includes a cylindrically bored body portion through which a polish rod reciprocates;

• the improvement comprising a blow-out preventing assembly, said assembly including a cylindrically bored resilient elastomeric substantially cylindrical element normally freely surrounding said polish rod and situated within said body portion, means to restrain said element from upward and downward movement within said body portion, an annular recess formed in the outer wall of said element defining, with the wall of said body portion, an annular fluid chamber, fluid conduit means through the wall of said body portion communicating with said chamber for the injection of fluid under pressure to engage said element in sealing relationship with said polish rod, and to close off said stuffing box completely if said polish rod is removed, said recess being bounded by an inner wall and a pair of side walls one each extending from the upper and lower sides of said inner wall respectively and inclining outwardly from said inner wall towards one another thereby defining annular upper and lower wedge portions which are forced outwardly to contact with said wall of said body portion by the injection of fluid under pressure, and sealing means surrounding said elements above and below said recess for sealing of said chamber.