| 摘要 |
<p>A packing tube for sealing the annular cavity around the pipe in a borehole, whilst high pressure grouting is carried out, is detachably assembled to pipes above and below so as to form part of a boring and injection installation. It has a central bore for the passage of drilling fluid or a filling material such as cement, and has a tubular elastic mantle forming a seal, the outer circumference of which, in its normal position is flush with the outer surface of the pipe. The packing tube consists of upper and lower halves which turn in one direction together, but can be displaced relatively to each other in the reverse direction, through a predetermined angle from a normal position to a second active position. Each half has a set of permanent magnets arranged around the central bores so that, whilst in the normal position the strins of pipes rotates in the forward direction for boring, when the pipe at the surface is turned back through a few degrees, the two sets of magnets are brought into alignment.</p> |
