The blow-out proof stem is one of basic design features of ball valve.

Ball valve stem is inserted from the valve body inside with integral T-type shoulder to provide blow-out proof effectively. It is internally inserted as a function of backseat to assure stem sealing safety.

To describe it in details, the stem is sealed by o-rings & packing rings, and held in position by the stem housing which is bolted to valve body. The o-rings & packing rings are compressed and held in position by the gland flange, which is bolted to the stem housing. That means when we replace the packing, the blow-out proof stem feature can prevent stem from being pushed out by the pressure from valve inside.