drawn into the loom t the circuit 14 is associated according to the invention with a programmable control circuit 15 to which it transmits its analysis signals from the circuit 15 prearranged for a specific preestablished working program of the loom t to which there correspond certain characteristic parameters operating periods strength and length of the air blasts output signals are sent both to the solenoid valves 7 8 and 9 and to the servo controls 10 11 and 12 in order to operate the same according to the program as a result of the analysis provided by the circuit 14 it is possible to continuously vary this program throughout loom operation according to the times taken for the turns of yarn f to unwind as determined by the sensor 13 and depending on the yarn 39 s physical characteristics this allows both the blowing periods and times of the nozzles 1 2 and 3 to be varied as well as the air pressures in the receivers 4 5 and 6 so as to obtain yarn feed conditions permitting the insertion of the weft yarn in an optimal time independently of any changes in the physical characteristics of the yarn itself which directly influence its unwinding speed on leaving the feeder a said speed corresponding to the times determined by the sensor 13 the logic adopted is that illustrated in detail in fig2 and specified hereinafter once.