Manhole Connectors for Polyethylene Pipes
Manhole Connectors fix PE pipes into Concrete chamber walls. A connector is necessary because, unlike rigid Ductile Iron or Clay pipes, PE pipes are subject to ongoing movement through temperature change and ground settlement. This causes small but constant changes in pipe length. This combined with expansion of the PE as the concrete cures means there is always a gap between the concrete and the pipe. If a manhole connector is not used, sewage and waste water will continuously leak from the chamber, polluting ground water, leading to erosion and sinkage.
There are two DSD approved connection methods given in the DSD Specification for Gravity and Stormwater Connections, Drawing Page 5 and Appendix 5A, Clause 5.7. these are Type A - Flexible connection and Type B - Rigid connection. Links to the DSD Drawing for Manhole connections and the material specification are given below.
DSD Drawing Page 5
DSD Appendix 5A
Type A - Flexible Connection
Also known as a Sliding Manhole Joint, this comprises of two machined PE components, independant of each other. The socket ring is plastered into the concrete chamber (non structural) and the spigot fused onto the PE pipe. The two components seal with O'Rings and a Hydrophilic expansion seal. This joint allows the pipe and spigot to move independently of the Socket ring in the chamber.
Movement due to temperature change (thermal movement) and settlement forces cause a change in the pipes length or angle, are not transferred into the chamber wall. These Socket/Spigot type joints allow for some vertical deflection (≤ 3º), so the chamber and pipe can settle independently of each other, and the pipe can change in length due to temperature, while still maintaining a water tight joint, with up to 5m of head. Typically only used in sizes up to DN525, larger sizes a Rigid Type B joint is typically used.
Advantages and limitations of Type A
Advantages of Type A Connections - In a Type A Joint the spigot end is welded to the pipe. When movement caused by a temperature change in the fluids, traffic loading or soil movement is applied, the spigot is free to slide a small amount inside the sockets rubber rings, but still maintain a watertight seal.
This flexible design means no force is applied to the socket ring or the chamber wall due to pipe movement, therefore the socket ring can simply be plastered in place (non structural). The socket ring does not need a structural connection to the chamber wall such, as there are no forces applied to the socket ring by the pipe.
Type A Flexible joints can be quickly installed as no structural Concrete / reinforcement / Corbels are required, the contractor can simply make a hole in an existing cast chamber wall and plaster the socket ring in, as the pipe is laid. See the images & Video below showing typical applications.
Limitations of Type A Connections - Type A are not suitable in reclaimed land, as ground settlement movement will likley be greater than the spigot length. Not suitable if the pipe is above ground as large temperature change will generate significant length change, both may pull the spigot from the socket ring over time. Also not suitable in installations where there is steep gradient between chambers (installed down a slope).
In these cases above, a Type B rigid joint should be casting the chamber walls and integrated with reinforcing to anchor the pipe ends into the chambers, the pipe is left to stretch and self relax when movement occurs.
Type A Flexible Connection example A
Type A Flexible Connection example B
Type B - Rigid connection (Short / Long)
Using the same principal and dimension relationships as a PE puddle flange, a Type B rigid manhole joint is machined from a single piece of hollow PE100 bar, with an embedded hydrophilic seal ring on the puddle edge. The theory of anchoring PE using puddle flanges is given here. The principal is that under tensile stress, the pipe will fail before the puddle pulls free of the concrete. Type B joints must be used in reclaimed land where future ground settlement will slowly stretch the pipe between chambers.
Advantages and Limitations of Type B
Advantages of Type B Connections - Type B joints are cast into the chamber wall with the reinforcing (not plastered in place like Type A) therefore they can withstand 100% of the maximum tensile force applied by the pipe so are perfect for reclaimed land, steep slopes, where the pipe is installed above ground. Type B long series can be cast into the wall on an Angle up to 30º and the excess spigot cut off after curing, saving repair plastering.
Limitations of Type B Connections - Because they are a rigid joint the forces created by temperature change in the pipe (length change) are transmitted directly into the chamber wall. Therefore, Type B connections should to be cast into the wall when the chamber is poured. In addition, the chamber wall must have sufficient cover over the puddle flange to transfer the tensile forces. This may add expense and means the pipes installation must be performed during chamber construction.
Plastering a Type B Connection in place may not withstand the forces created by thermal change and may break the joint out. Breakout forces can be calculated using the degree of temperature change, the length between chambers and estimated soil friction.
Type B Rigid Connection Example