the region of the appurtenant feed which upon the first revolution of the needle cylinder displaces the connected 3 2 way pneumatic valve 15 into a position in which a pressurized air impulse of short duration is passed from the source through the corresponding check valve into duct 10 as a result chamber 18 is pressurized lifting the piston 4 whereupon pawl 11 is also lifted out of engagement with the slot 16 by this action spring 13 causes the lever 1a to pivot counterclockwise in the direction of arror b swinging the guide 1 into operative position as shown in fig2 as the pawl 11 is released from slot 16 it is caused to slide over the edge of the hub fig5 which because of its curvature acts to additionally force the piston 4 into its uppermost position simultaneously the piston 5 which moves freely in its cylinder 5a is moved by the rear arm of the lever 1a into its upper position the check valve 14 does not permit any pressure drop in line 10 due to feed back and thus the correct operation is assured even with short duration air impulse when guide 1 has however reached its operative position secured by spring 13 then air slowly escapes from below piston 4 and the pawl 11 due to the lack of sealing in its mounting in the body 6 the guide is held in the operative position throughout knitting by the bias of spring 13 in order to disengage the yarn guide 1 from its operative position the switching of one of the 3 2 valves 15 leading to duct 8 is effected from machine control drum or the control chain this valve 15 is brought.