in the regulating organ facing the inlet conduit 4 if the regulating organ 6 is rotated further an intermediate flow u201c qint u201d will be supplied by way of an ensuing flow opening 17 in the form of a groove which has a decreasing area being substantially lower than the qmax the u201c qint u201d flow is diminishing in accordance with the angle a rotated until a through hole 18 for a u201c qmin u201d flow is facing the inlet conduit 4 at an correspondent angular position a2 210 degrees the diameter d1 of this hole 18 is calibrated for the supply of a qmin of ng on the ng type cooking appliance the knob class provided with the appendix 14 cannot turn through an angle larger than a2 the external control panel 2 fig4 has a circular groove 20 travelled by said appendix 14 of the knob 9 its angular extension a2 210 degrees imposes the limit of angular travel governing the regulating organ 6 from the off position to the outlet of the ng qmin flow by way of hole 18 once installed on the panel 2 the knob unit 9 chosen for the supply of lpg lacks in having said appendix 14 or any other element limiting the angle u201c a u201d of rotation thus the regulating organ 6 may rotate as far as an angular position a3 270 degrees located farther away from the initial off position than the prior position u201c a2 u201d until a second through hole 19 lines up with the inlet conduit 4 the diameter d2.