| 摘要 |
<p>991,012. Advancing mine roof supports. DOWTY MINING EQUIPMENT Ltd. May 21, 1963 [May 25, 1962], No. 20179/63. Divided out of 991,007. Heading F1P. In a roof support assembly wherein a series of roof supports are automatically advanceable in a predetermined sequence when supplied in turn with fluid under pressure from a line 11, a sequence stoppage indicator 18 including a warning device 24 is arranged to indicate, during an advancing sequence, the existence of a predetermined pressure in the line 11 for more than a predetermined period of time. The indicator 18 comprises a pressure gauge 19 supplied with fluid from the line 11, and having a pointer 22 which completes the circuit to the warning device through a contact 22 and a pressure switch 25, when the pressure exceeds a predetermined maximum. The pressure switch 25 ensures that the warning device is operative in response to maximum pressure only during an advancing sequence. The device 24 incorporates a delay mechanism to prevent operation due to normal pressure fluctuations associated with support advancing operations. A further contact 27 is engaged by the pointer 21 should a low pressure in the line 11 occur at any time for more than a predetermined period. Specification 991,008 also is referred to.</p> |
