| 摘要 |
A mine prop comprises an elongate substantially rigid support member (10) including a biassing device (11) adapted to extend the effective length of the support member when there is a divergence between a hanging wall (20) and foot wall (21) between which the prop extends. The biassing device (11) comprises a pneumatically biased expansion device. With such an arrangement controlled yielding of the prop (10) can also be achieved by providing a pressure relief valve (18) for releasing fluid from the expansion device at a predetermined pressure. |
