Introduction to CMC

2.yìn-jǐng, called manhole in Hong Kong, Macao and Guangzhou, is an underground space for transit and control of urban underground pipelines. Its ground entrance and exit is called Shajingkou or CMC. Manholes are usually covered by manhole covers.

3. In cities, all public water supply, sewage pipes, telephone lines and optical fiber networks may be connected through underground passages under inspection wells. Manhole is its exit to the ground and is covered by manhole cover. Underground pipelines are mostly straight. When steering is needed, a manhole is arranged at the steering position, so that the straight pipeline is not easy to be blocked and the pipeline is easy to install. In addition, in order to facilitate work and safety, a manhole will be set in the middle of a certain length of pipeline to facilitate access to the pipeline.

4. In sewage treatment engineering, manholes with different designs can have different functions, such as degrading manholes and dividing manholes. Degraded manholes are manholes where water enters the bottom of manholes from high places and consumes kinetic energy, which can reduce the kinetic energy of water and is suitable for draining water from high places to low places. Sand-separating manhole is a manhole whose bottom sinks to collect garbage.

5. Because the canal under the manhole cover is a sealed site, the concentration of methane, carbon dioxide and other gases is often too high. Cleaners, canal repairers, telephone line technicians, firefighters and other personnel need to use ventilators to introduce fresh air on the ground before entering work to avoid occupational disasters caused by lack of oxygen or gas explosion.