Abstract: Ring injectors for aerating fluids, useful for example in flotation systems, have a housing with a mixing section, in which air is added to the through-flowing fluid through an annular slot. A core is arranged in the center of the mixing section. An air-solid mix is formed in the mixing section by deposition of air bubbles on solid particles. An annular injector with a slot width (Q.sub.2) that leads into the airing chamber with a minimum opacifying speed of 2.0 m/s at the inlet of the aerating chamber, has an annex mixing and dispersing section (6) with a cross-section that remains the same until the end (12), as well as a middle piece (10) centrally arranged therein also having a constant cross-section, the length of the mixing and dispersing section (6) being 20 times the width of the annular slot (Q.sub.3). The distributing cone (2) and the middle piece (10) can be screwed together or inserted into each other. The air slot can be regulated by spacing rings (13).

Abstract: An electronic control method and apparatus for controlling the sloughing strokes in sloughing machines for coal and other minerals, has a stroke frequency generator which supplies recurrent signal codes to parallel-connected inlet and outlet stroke generators. Power amplifiers are connected to the stroke generators for amplifying command pulses therefrom, the pulses being supplied to inlet and outlet valves of the machine. A signal code is supplied from the stroke frequency generator through a divisor in a freely selectable clock sequence to the outlet stroke generator or alternatively the divisor releases the command pulse from the outlet stroke generator to the outlet valve in a freely selectable clock sequence.