Mine hoists

In a mine winder of the type having two load-carrying cables wound in opposite directions around respective drums incorporating for each cable and its associated cable-supporting drum a braking mechanism, said braking mechanism comprising motion-sensitive means for sensing the immediate operating conditions of the cable, said motion-sensitive means incorporating one element the position of which is variable according to the amount of cable paid out from the drum and a second element arranged to occupy one of two possible extreme positions, one of which corresponds with most of the cable paid out or most of the cable reeled in and the other of which corresponds with positions of the cable between these extreme positions, the positions of these two elements constituting mechanical signals, and a cable movement detector arranged to sense whether the cable is moving above or below a predetermined minimum speed and if it is moving above said minimum speed in which direction and to generate a corresponding signal, pressure operated braking means for controlling the rate of movement of the cable, brake control means including air pressure control means operative to provide at least two separate supplies of air at different pressures and means for varying the pressure of the supply at the higher pressure between a minimum and a maximum value, said last mentioned means being arranged to receive a signal from said one element and to act according to the signal received to vary the air supply pressure, a changeover valve connected to the air pressure control means and having operating means arranged to receive a signal from the cable movement detector and thereupon connect an output from the valve to either of said supplies of air according to the signal received, two air flow restricting devices connected between the outlet of the changeover valve and the braking means and arranged to provide individually different time delays in the build-up of pressure across the devices, and a time delay selecting device having operating means arranged to receive a signal from said second element and to act according to the signal received to render effective the appropriate air flow restricting device.