Over-or under ground piping: accessibility, insulation, blockage.

地上或者地下管道：就近原则，隔热处理，阻塞问题。

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Plastics piping systems for buried and above-ground drainage and sewerage under pressure - Unplasticized poly (vinyl chloride) (PVC-U) - Part 1: specifications for piping components and the system.

地下和地上排水和排污用塑料压力管道系统。未增塑聚氯乙烯(PVC - U)。第1部分：管道件和系统规范。

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