Manholes made of plastic material can be moulded according to the needs of the project, so we cannot speak of standard dimensions.
However, a distinction must be made between manholes made from tubing and those made by rotational moulding. The latter consist of a moulded EPDM base with a circular cross-section, the dimensions are therefore constrained by the moulds owned by the various manufacturers.
Polieco, for example, offers its customers six different types of bases depending on the base geometry, the diameters of inlet and outlet pipes and the riser diameter.
Dimensions of moulded plastic manholes
The upper part of the ND/OD 800 – 1000 – 1200 moulded manholes can be made with an EPDM conical adapter obtained by rotomoulding and engaged on the coupling extension to taper the manhole up to ND 600 mm for the crawl space.
In the last few years, the use of a special tee obtained from rotomoulding and used as a manhole is widespread on the European market. This product also has a size limitation dictated by the moulds used by manufacturers. Polieco’s range offers three-sided tee manholes in diameters from ND/OD 400 to ND/OD 1200. In this case too, the upper part equipped with a spigot is connected to the risers of corrugated pipe and the conical adapters (for diameters ND/OD 800 – 1000 – 1200).
When it comes to custom-made manholes, there are no limits to the through-pipe diameter and any type of manhole can be made according to the engineer’s drawing. In this case too, the end of the manhole can be made with an EPDM conical adapter obtained by rotomoulding and engaged on the coupling extension to taper the manhole up to ND 600 mm for the crawl space.