| 摘要 |
<p>The invention relates to a method for replacing or preparing an existing main, particulary an cast iron gas main, with a new main. The new main may be of any convenient plastics material such as polyethylene or pvc. The method comprising fracturing the existing main and maintaining sufficient clearance through the fractured main for movement therethrough of a new main or a liner for the fractured main. The liner is of a much tougher wear resistent plastics material and serve as a protective sleeve for the new main when the new main is subsequently moved into the liner.</p> |
