How to make a design choice for the structural forms of manholes and access holes?

1. The design choice for the structure of manholes and access holes should be determined based on factors such as the frequency of opening the cover, the installation location (horizontal or vertical), the required level of sealing, the weight of the cover, and the space occupied when the cover is opened. 2. When the manhole cover needs to be opened and closed frequently, quick-opening manholes or hand holes are recommended. If the vertical plane position of the manhole axis is small, a rotary quick-opening manhole or handhole can be selected ； If rapid opening and closing is required, and it is permissible for the cover to move left and right perpendicular to the axis, a lever-type quick-opening manhole or handhole can be selected. 3. To prevent dead zones where the flow of the medium is halted or severely restricted due to the sections of manholes and access holes, core-equipped manholes and access holes should be used. 4. When the weight of the manhole cover exceeds 35 Kg, a hinged manhole cover should be selected. 5. Atmospheric manholes and handholes are only suitable for non-toxic and non-explosive media. 6. The selection of the nominal pressure class and seal face type for manholes and handholes is the same as that for pipe flanges. 7. Manholes located at the bottom of a container or at a higher position (more than 2 m above the ground or operating platform), or those designed for temperatures below -10°C, shall have lids supported by lifting rods or hinges.