PVC-U Underground Branches, Junctions & Y-Branches
Junctions bring branch drains into the main run. Below ground the 45° Y-branch is the standard fitting, because it sweeps the incoming flow into the direction of travel rather than across it.
Also searched as: underground junction, Y branch, drainage junction, equal junction, unequal junction, saddle connection
Equal and unequal
Equal junctions join same-size runs — 110 × 110mm and 160 × 160mm are the volume items. Unequal junctions such as 160 × 110mm and 200 × 160mm bring a smaller branch into a larger collection drain without an extra reducer. Level-invert patterns keep the soffits aligned so solids are not lifted at the junction.
Angle
45° is the correct choice for almost all buried work. The 87.5° junction is available for tight situations, but it should be avoided on any run that carries solids because flow entering square against the main flow causes deposition immediately downstream.
Connecting into an existing drain
Where a new branch has to be cut into a live drain, use a saddle connection or a pair of slip couplings with a short branch assembly. The method for the coupling approach is set out in the Underground Installation Guide and meets BS EN 1610 clause 9.2.