Patent GB-1019212-A (GB)
Title: Improvements in and relating to tensioning means for endless conveyor belts
IPC: B65G23/44
Filed: 1962-12-11
Abstract: 1,019,212. Endless conveyers. G. A. BLACK, and E. H. HANDS. March 10, 1964 [Dec. 11, 1962; July 12, 1963], Nos. 46787/62 and 27670/63. Heading B8A. An end roller of a belt conveyer is tensioned by one or more hydraulic rams 2, Fig. 6, to which the roller is attached, the rams being connected to gas-filled hydraulic accumulators 1, and a boost pump 51 is provided to maintain a substantially constant pressure in the ram as the accumulator pressure falls. The pump 51 draws oil from the accumulators through an unloading valve 41, and a second pump 52 drawing oil from a tank 44 delivers it through a non-return valve 53 to the accumulators, the two pumps being driven by a common motor. The pump 52 has a relief valve 46. In operation, when the conveyer is started, oil passes from the accumulators 1 via a non-return valve 3 to the rams 2, the resultant small pressure drop being detected by a pressure switch 50 or by the relief valve 46 to cause the pumps 51, 52 to start pumping, the pump 51 delivering oil through a non-return valve 45 to the rams and the pump 52 delivering oil to the accumulator to offset leakage. When the extension of the belt has ceased the slight rise in pressure is sensed by the valve 46 or the switch 50 and, if the pumps are run continuously the valve 46 unloads the pump 52, this unloading operating the valve 41 to allow the pump 51 to circulate oil in a closed circuit through ports b and c, thus unloading the pump 51. If the belt tension is too great for the belt loading conditions oil is forced back so the accumulators via a variable balance valve 40 which thus measures the total extension of the rams and so alters the pressure difference between the rams and the accumulators to accommodate for the change of pressure in the latter. Pressure surges and any over-delivery of the pump 52 causes fluid to pass through a relief valve 48. In a modification, Fig. 5 (not shown), a hydraulic motor operated by oil from the accumulators drives the boost pump, the pump 52 being dispensed with and the relief valve 46 being associated with the boost pump; the boost pump external driving means is thereby reduced in horse-power. The output of the boost pump is greater than the hydraulic motor to provide a pilot supply for operation of the valve 41 when the valve 46 is closed by reduction of pressure in the ram cylinders, and to charge the accumulators. In a second embodi-, ment, Fig. 1, accumulators 1 are connected to rams 2 through non-return valves 3, 4, the rams being return-connected to the accumulators through a pressure relief valve 5. A pump 7 controlled by a pressure switch 9 and associated with a storage tank 10 is connected to a point between the valves 3, 4, the pump 7 being supplied from the accumulators through a solenoid operated selector valve 12. Pressure surges are provided for by a relief valve 6. When the accumulators have to be recharged due to leakage the pump 7 is started by a pressure switch 11 and is connected to the accumulators through the valve 12. The ram assembly, Fig. 2, consists of five rams 20 ... 24, the rams 20 ... 23 being mounted on a carriage 25 and the ram 24 being mounted on a carriage 31, the carriages having rollers 26. The effecttive areas of the rams and the disposition thereof are such as to ensure that the rams operate telescopically. In an alternative assembly, Fig. 7 (not shown), two pistons are provided one of which is disposed inside the other for telescopic movement, the latter being transmitted to the end roller of the conveyer by wire ropes arranged over pulleys to give a movement of the end roller which is three times that of the stroke of the cylinder assembly. In a modification only one piston may be provided.