body 3 surrounding the chamber sleeve 2 with an entry diameter which is equal to the diameter with which the transition 10 opens into the facing end of the chamber sleeve 2 from this point on the nozzle bore 15 tapers conically the corresponding bore having an apex angle u03b2 up to a narrow point 16 from whence the nozzle bore 15 again conically widens up to the free end of the nozzle body 3 with an apex angle u03b5 for the corresponding cone thus originating from the water entry nozzle 9 up to the remote end of the nozzle body 3 an inner space is formed which is rotational symmetrical with respect to the major axis 4 and which extends firstly over the length of the chamber 7 cylindrically then conically widens near the end thereof then conically tapers in the adjoining nozzle body gradually up to the narrow point 16 and from there again conically widens until the exit from the nozzle body 3 in a preferred example of embodiment the chamber sleeve 2 comprises a total length of 90 mm the bore 5 having substantially a diameter of 6 35 mm the chamber 7 a diameter of 21 mm the opening from the chamber sleeve 2 to the nozzle body 3 an opening.