ft型投入式止回阀是钻柱内防喷器。该工具结构简单，操纵方便，只要缷开方钻杆的接头螺纹便可以投入钻杆的水眼内就位后就能达到内防喷的目的。投入式止回阀由凡尔接头和止回阀总成两部分构成。凡尔接头与止动环用螺纹连接并上紧扣和钻柱连接下入井内，在未投入止回阀总成时，作为钻柱上的一个接头。

ft type drop-in check valve is a kind of insied 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.