50 is then inserted a strong downward force is exerted by the oil well fluid on the adjusting mandrel in addition to the restoring force due to the fact that flow channel 7 is blocked at the lower end and this downward force causes adjusting mandrel 33 to move into the lower end position illustrated by 33b in this end position the oil well fluid is forced to flow out of flow channel 7 at the upper end of adjusting mandrel 33 and past gasket 39 through slit openings 8 with the result that the oil well fluid flushes out any solid particles that might be deposited in the gap openings 18 19 with such a downward movement induced by valve body 50 the lower end of adjusting mandrel 33 comes into engagement with a stop element which in the practical example according to fig4 is also designed as a fixing element namely as a slotted radially expandable fixing ring which rests in an internal groove 52 in part 6 of casing 3 this stop and fixing element which may also have any other suitable design defines the lower end position for adjusting mandrel 33 and also secures it when the pumping of oil well fluid is concluded so the oil well fluid present in the drilling shaft above valve body 50 can escape into the borehole for the sake of drainage when the drilling shaft is pulled up for the next operation of the deep well drilling tool valve body 50 is removed from the stabilizer and the adjusting mandrel 33 is pushed up out of engagement with the stop and fixing ring 51 which can be accomplished for example as part of an above ground maintenance job by a tool inserted from beneath after unscrewing casing part.