FT type drop-in check valve is a kind of Iside BOP(blowout preventer)in the drill string.It is simple in structure and easy to operate.When blowout is going to be happened,the thread Connections of the kelly are screwed out immdiately and back pressure valve sub is into the I.D. of drill pipe and then pumped downward to the required place.Thus the blowout accident can ba prevented.Drop-in check valve consists of back pressure sub and check valve assembly.Back pressure sub is connected with stop ring and tightened on and put into downhole with drill string.back pressure sub is used as a sub above drill string before check valve assewbly is run in downhole.