actuator 8 which is adapted to restore the tension to the desired reference value thus if there is less tension the braking action will be increased thereby to increase the tension of the yarn f on the other hand if the tension is higher the braking action will be reduced in order to reduce the tension of the yarn f a further embodiment of the system according to the invention which it has been deemed superfluous to illustrate in the drawings provides for the use as an alternative to the signals from the warp stop motion device of signals representing the value of weft yarn tension sent by a sensor suitably a tensiometer provided for the specific purpose of the invention said tensiometer may be positioned upstream or downstream of the warp stop motion device 5 as long as it is on the path of the weft yarn between the weft feeder and the loom in this case the warp stop motion device may be of the conventional type it is to be deemed that the system thus modified even if less economic than those heretofore described and illustrated by fig1 and 2 turns out to be more efficient as it can make use of a sensor more adaptable to the purposes of the invention with each of the described embodiments of the system according to the invention according to the nature and type of interaction between the actuator and the brake means usually mechanical or magnetic it will be possible to rely on.