A compacted yarn is produced by providing a row of orifices subsequent to drafting along which the fiber strand is guided and after which the fiber strand is subjected to a twist according to the invention the suction air flow is monitored at least at one suction location and upon falling below a threshold, a signal is generated which can be used for shutdown or to alert personnel. The result is elimination of the reduction in yarn quality which can occur when the compaction system becomes blocked by lint, fiber accumulation or the like.