在流入城市下水道中的生活和工业污水中,含有沙子、砾石和碎石块,有的甚至是石头的粗粒杂质。这些物质能引起净化构筑物中的泵站设备、压力管和干管的磨损。对城市排水工程系统的管道磨损往往忽略不计,因此,对其不够重视,然而,应当把它看作是客观存在且不可避免的,在某些情况下,磨损发展很快,并造成破坏。例 The living and industrial wastewater that flows into the city’s sewers contains sand, gravel, and crushed stones, some of which are even coarse-grained impurities of the stone. These substances can cause wear of the pump station equipment, pressure pipes, and dry pipes in the decontamination structure. The wear of pipelines in urban drainage engineering systems is often neglected. Therefore, they are not given enough attention. However, they should be regarded as objective and unavoidable. In some cases, wear and tear develops quickly and causes damage. example