Keep proper length of pipe when put into the manhole .
布放后应保留适当长度于引进端人（手）孔或拉箱内。
2
Two alternative methods can be adopted, one being to provide a ventilation pipe fixed to a building and carded above the eaves level, and the other to have ventilated manhole covers.
有两种解决办法，一种是安装固定在建筑物上高度超过屋檐的通气管，另一个使用通风检查井盖。
3
Main products include ductile manhole covers, composite resin covers, drill rod cement covers, galvanized steel grating, polymer alloy covers, cast iron manhole covers, flower bar, cast iron pipe.