Drop-In Check Valves prevent return flow during a kick and are suitable for most drilling situations in which return flow through the drill string is a risk and normal operation requires the benefits of a full-bore sub. By preventing upward flow through the drill pipe, but allowing fluid to be pumped downward to circulate the well, the valves provide the driller with the means to control the drill pipe pressures when required, significantly improving and simplifying well control. When blowout is going to be happened, the thread connections of the Kelly is screw out immediately and put the check valve is into the drill pipe and then pumped downward to the required place. Thus the blowout can be prevented.