Abstract: Gas, particularly methane, is sucked from a borehole (B) extending from a coal mine working by means of a casing consisting of tubular plastics sections (8) by means of a vacuum pump connected to the lower end of the casing. The casing is sealed to the borehole by a sliding seal (2) which allows the casing to be moved up and down the borehole until the upper end of the casing is at the level of the maximum yield of gas. The annular space between the casing and borehole wall is then filled with a liquid which expands and sets to form a polyurethane foam (4).

Abstract: In a stone cutting machine having a cutting chain rotated by a motor and a separate power feed for the machine, the power consumption of the drive motor is monitored. When the power consumption falls below a minimum, a control signal is generated to increase the feed, and when the power consumption exceeds a fixed maximum, a control signal is generated to decrease the feed. In generating the control signal, the power consumption is scanned only over a pre-determined period, which for power consumption beneath the minimum is approximately twice as long as for the power consumption above the maximum.