Patent GB-993670-A (GB)
Title: Roof support assemblies suitable for use in mines
Inventor: POTTS MICHAEL CHARLES
IPC: E21D23/16
Filed: 1962-10-10
Abstract: 993,670. Advancing mine roof supports. DOWTY MINING EQUIPMENT Ltd. Oct. 2, 1963 [Oct. 10, 1962], No. 38395/62. Heading F1P. A high pitch warning bell 32 Fig. 3 responsive to pressure in the main line 11 Fig. 2 supplying a series of sequentially advanced mine roof supports 4 sounds at the start of advance of each unit towards the coal face but during the advance of each unit gives way to a low pitch bell 29 responsive to the fall in pressure in said line 11. The bells thus sound alternately and at the completion of advance of the last unit 4 of the series the high pitch bell 32 is inoperable whereas the low pitch bell remains operable. A plurality of high pitch bells 33 in parallel with bell 32 may be arranged along the working face. The roof supports are arranged in groups of four the first of which has a conveyer advancing jack 8 Fig. 1 (not shown) and each support 4 is controlled by a valve 13 connected by lines 14, 15 to main supply and return lines 11, 12 and to a source 10. Each valve is connected in series in a pilot line 17 and a pressure source 16. Pressure in line 17 actuates a valve 13 to initiate advance of its associated roof support unit and when the props have been reset the pressure therein actuates valve 13 to admit pilot pressure through line 17 to the next support when the props of the end support of a group have been reset pilot pressure is admitted past a non-return valve to a line 18 and cuts off source 16 from line 17 and connects the latter to exhaust. Prior to advance of the succeeding group of supports the conveyer is advanced and jack 7 operates a valve 19 so as to transmit pressure from line 18 first to a line 21 leading to the warning system 23 and then to a line 22 leading to the pilot pressure source which is then reconnected to line 17 to pressurize it and thus initiate advance of the first of the four units of the group of supports. At this time pressure in lines 18, 21, 22 is lost. In operation and assuming no advance taking place a switch 39 is closed by an actuator 42 subject to high pressure in line 11, a two way switch 41 is moved by an actuator 43 subject to pressure in line 18 to connect switch 39 to resetting mechanism of a counter 31, a switch 48 is opened by an actuator 52 also subjected to pressure in line 11 and a switch 46 is held open by an actuator 47 connected to line 21 which is unpressurized. Consequently bells 32, 33 do not operate. Near the completion of conveyer advance, valve 19 is operated and line 21 pressurized resulting in switch 46 closing to complete the circuit of the high pressure bells 32, 33. Then as pilot line 17 is pressurized and the first roof support unit is advanced pressure in line 11 falls sufficiently to cause motor 42 to open switch 39 and to cause motor 52 to close switch 48 thereby breaking the high pitch bell circuit and closing the low pitch bell circuit and that of counter 31. On completion of advance of the particular unit pressure in line 11 rises and thus opens switch 48 and closes switch 39 whereon the high pitch bells alone operate. When the end roof support of the group has completed its advance pressure in line 18 operates motor 43 to cause switch 39 to be connected to counter 31 which is reset to zero; operation of bells 32, 33 being prevented until another advancing sequence commences. Specification 991,008 is referred to.