Air shooting system for the mining of coal or the like

In an air shooting system for a set of shot holes in a coal seam or the like, the combination comprising a set of tubular shooting heads dimensioned to fit in the respective shot holes and each having a head inlet at the near end supplied by an individual feed line, a reservoir in the head fed by the inlet, means defining a discharge port adjacent the far end of the head, each shooting head having a valve mechanism interposed between the reservoir and the discharge port for blocking the discharge port as pressure is progressively built up in the reservoir, the valve mechanism including pressure responsive means for suddenly opening the discharge port as the pressure reaches a triggering level to release pressurized air in the shot hole for splitting of the seam, a source of high pressure air, a manifold connected to the source, a set of automatic shut-off valves interposed between the manifold and the individual feed lines, each shut-off valve having an inlet and an outlet and having a movable shut-off valve element interposed between the inlet and outlet for controlling air flow through a restricted air passage, the movable valve element being exposed on opposite sides to the pressures at the inlet and outlet and biased into a normally open position to permit gradual flow of air through the restricted air passage to the outlet but with the differential pressure resulting from the sudden drop in pressure at the outlet, as discharge occurs at the associated shooting head, serving to snap the valve element into closed position cutting off further flow, the valve element being thereafter held in closed position by the pressure at the inlet, the pressure responsive means in the respective shooting heads being adjustable to trigger at incrementally spaced levels in a predetermined series so that, as air pressure is built up simultaneously in the reservoirs of all of the shooting heads, the shooting head lowest in the series is triggered for discharge causing a sudden drop in pressure at the outlet of the associated shut-off valve thereby shutting off further flow of air thereto and isolating such head from the manifold to prevent loss of manifold pressure, with the process being repeated for each successive shooting head in the series until all of the shut-off valves are in closed condition, and means including a manual control and re-set valve interposed between the source and the manifold for cutting off flow of pressurized air from the source to the manifold and venting the manifold to remove pressure at the inlets of the shut-off valves so that the valve elements thereof are restored to normally open position to achieve prompt simultaneous venting of the feed lines preparatory to removal of the shooting heads for re-location in a succeeding set of shot holes.