Float valve Sub ( bit sub) usually connect the top of the drill bit. They used to  control the bottom hole fluid. When stopping pump and make up a joint, they can prevent the reverse flow of drilling cuttings. When there is a well kick, they can prevent fluid flows into the drilling tool. They have the effect of down hole blowout preventer.

According to the connection forms of the body, it can be divided into two kinds of  typeAand type B. Type A Float Valve Sub is upper BOX and lower PIN, Type B is double BOX. Their  internal structure are similar.As shown in figure1,2.

                                                                                                                                                                                                                                                           1. body 2. Float valve
                                                   Figure1, typeAdrill pipe float valve

                                                        1.body 2.float valve

                                                Figure2. Type B drill pipe float valve

According to the structure of valve core, it can be divided into Model F and Model G.