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Phreatic safety sign is an auxiliary device which is attached to the well cover. It consists of
a warning tragle, a spindle and a torsion spring, which produces an elastic force .
With the help of the torsion produced by the torsion spring, the warning tragle of this device can rise automatically , and gradually become erect, warning the pedestrians and vehicles.
HuSonglin Linxie Yangxue ZhangXiaoqiong