106 and an oblique bore 108 an angle 109 of about 30 u00b0 is advantageously defined between the axial bore 106 and the oblique bore 108 the diameters of the axial bore 106 and of the oblique bore 108 are advantageously about 3 to 5 times smaller than the inlet diameter 110 of the inlet cone 104 in fig6 they have for example approximately the same diameter as the constriction 40 of the venturi nozzle 36 with reference to fig1 a first embodiment of the valve control of the gas feed will now be described in more detail both solenoid valves 32 32 u2032 closed in the absence of current are controlled by a pressure switch 60 which applies water pressure in the drinking water pipe 10 if the water pressure in the drinking water pipe 10 is smaller than a predetermined pressure p 0 then both solenoid valves 32 32 u2032 are provided with current and are opened if the water pressure is greater than the pressure p 0 only the solenoid valve 32 u2032 is provided with current and is opened in other words if the water pressure is smaller than p 0 the gas flows via both gas channels 54 54 u2032 into the constriction 40 of the venturi nozzle 36 if however the water pressure is greater than p 0 the gas only flows via one of the two gas channels 54 54 u2032 in the constriction 40 of the venturi nozzle 36 the pressure switch 60 may naturally also be replaced with a pressure sensor which is connected to an electronic circuit device which then controls the solenoid valves 32 32 u2032 reference number 62 indicates a switch which allows the current supply of both solenoid valves 32 32 u2032 to.