How to Guide

122
Plastics Technical Manual
Occasionally a designer will specify Schedule 80 PVC pres-
sure pipe meeting ASTM D 1785 for a DWV application in
combination with Schedule 40 PVC DWV (Drainage) fittings
meeting ASTM D 2665. Typically the application is under-
ground and the designer is interested in specifying a pipe that
is more robust than standard Schedule 40 PVC.
Charlotte Pipe does not recommend using Schedule 80 pipe
in combination with Schedule 40 DWV fittings due to the
dimensional mismatch between these products. Schedule
80 pipe has a significantly smaller inside diameter (ID) than
Schedule 40 pipe. When Schedule 80 pipe is installed in a
DWV fitting hub, the reduced ID of Schedule 80 pipe forms a
restriction or ledge at every fitting hub that will impede flow,
possibly leading to buildup and clogs. Additionally, Schedule
80 PVC pipe is not marked or listed in the model plumbing
codes for DWV applications. ASTM D 1785 is exclusively
a standard for pressure-rated pipe. Additionally, pressure-
pattern fittings do not have a sanitary turn which is neces-
sary to allow waste to travel through the fitting unobstructed;
therefore, Schedule 80 pressure-pattern fittings would not
be an appropriate product for the application. There is no
ASTM standard for Schedule 80 DWV fittings and except
for some large-diameter fabricated fittings, no Schedule 80
DWV fittings are offered by any U. S. manufacturer.
If Schedule 80 pipe is being specified for a DWV application,
it is often motivated by a desire for a more robust product
with greater earth / live load carrying capability in under-
ground applications. In these instances Charlotte Pipe rec-
ommends Cast Iron Soil Pipe for the application as it is a
robust product with the ability to resist tremendous earth and
live loads. In contrast, PVC pipe is a flexible conduit which
is dependent upon the support provided by the surrounding
soil for its ability to withstand external loads.
If the designer determines that PVC is the best material for
a commercial DWV application, Charlotte Pipe recommends
Schedule 40 DWV pipe and fittings that conform to ASTM
D 2665; this will ensure a Schedule 40 solid-wall PVC pipe
SUPPLEMENTAL INFORMATION
PVC Schedule 80 Pipe for DWV Applications
product that is more robust than cellular or foam-core pipe.
Cellular or foam-core Schedule 40 pipe conforms to ASTM F
891, is lighter, has reduced pipe stiffness, reduced resistance
to mechanical damage, and most specifiers believe it is less
appropriate for commercial applications. PVC pipe should
always be installed underground per ASTM D 2321. For pipe
being installed in unstable or unusual soil conditions, addi-
tional installation procedures may be required. Consult a soil
expert and/or structural engineer for guidance. Plastic pipe
suspended from an on-grade slab must be installed in accor-
dance with ASTM F 2536.