| 摘要 |
Device preventing the introduction of foreign bodies inside an access tube for operating buried valves D. It consists of a metal body A receiving a sealing washer E which is interchangeable by means of a system of rings G + F and of bolts I. Under the thrust of a key for operating the valve, the membrane opens and then closes again after this key has passed through. The device according to the invention is particularly intended for preventing any introduction of gravel or pebbles to the bottom of an access tube for operating a valve which would make this operation impossible. <IMAGE>
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