| 摘要 |
A tank contains a first chamber having a bellows-type elastic wall and has a normally open valve through which the chamber is connected to an oil-filled cable and when the chamber wall contracts sufficiently the valve is engaged by the wall and closed. The first chamber is surrounded by a fluid filled second chamber which is connected to a source of fluid through a similar valve which is normally open but which is closed by contact with a wall of the first chamber when the wall thereof expands by a predetermined amount.
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