| 摘要 |
1,233,188. Hydraulic mine roof support. GULLICK DOBSON Ltd. 21 Feb., 1969 [22 March, 1968], No. 13950/68. Heading E1P. When ram 11 and hydraulic roof support 10 are retracted simultaneously to move the roof support nearer to the working face shuttle valve 20 is closed and fluid from the ram passes to the exhaust line 14, similarly fluid from the roof support 10 passes through control valve 15 to exhaust line 13, neither exhaust streams affecting the working of the other device. Control valve 15 is used to connect supply 12 to prop 10 and to connect supply 12 to side 11b of ram 11 when shuttle valve 20 is open or to connect the supply to side 11a of ram 11 when shuttle valve 20 is closed. If back pressure is low then only one exhaust line may be used. A non return valve 21 may be provided on the exhaust line from ram 11. |
