compaction chamber 1 is adjustable and in that the pre setting and guiding chamber 5 has a cross section greater than that of the compaction chamber and therefore greater than that of the sliver of resultant crimped yarns 6 the supplementary space or spaces defined around the sliver 6 being related to the delivery means of the pre setting fluid the compacting chamber 1 which is made up of driving rollers 2 and doctor blades 3 is adjustable in its cross section owing to the provision of means 7 and 8 which allow on one hand a coming together of the two doctor blades 3 and on the other hand a displacement of the inlet section of the doctor blades 3 in the direction of or away from the driving rollers 2 the adjusting means 7 which allows the coming together of the two doctor blades 3 is illustrated in fig4 of the accompanying drawings in the form of a reverse threaded element or screwed element but may also very well be in the form of a pair of synchronized jack screws or an articulated control rod assembly bringing together or spreading apart the doctor blades 3 the means 8 which is intended to produce the displacement of the doctor blades inlet in the direction of the driving rollers 2 or in the opposite direction to these driving rollers 2 is illustrated simply in.