Installation Guide

Installing PVC Pipe in Underground Applications

Switching a commercial plumbing system from cast iron to plastic takes more than just changing materials.

Installation requirements change, and failure to address these dierences may result in your plumbing system failing.

Key Points to Remember

Bedding and Backll

Proper bedding and backll include digging a larger trench and taking extra care

when installing the foundation and bedding. Also, the pipe must be compacted to

the spring line of the pipe to help PVC and ABS withstand external loads.

VE_PVCUnderground2015

Trench width is too narrow, two pipes

buried directly adjacent to one another and

improper bedding

Bedding and backll requirements are outlined in ASTM D2321 (Standard

Practice for Underground Installation of Thermoplastic Pipe for Sewers and

Other Gravity-Flow Applications), which is often included in the engineer’s

specication for installation.

Please note these additional steps are necessary because PVC and ABS do not

have adequate stiness to resist earth and live loads. Failure to meet these

requirements may result in the system collapsing and failing.

Incorrect Underground

Installation

Elevated Temperatures

The Iowa formula uses pipe stiness in combination with soil type, trench design and other factors to determine maximum burial for

exible systems like ABS and PVC. As shown in the table below, at 140°F only 22% of PVC pipe stiness remains. If high-temperature

discharges from commercial dishwashers, boilers, water heaters, temperature and pressure relief valves or other equipment are not

tempered before entering a plastic DWV system, softening of the pipe can occur resulting in collapse or failure.

4” PVC DWV Solid Wall Pipe (ASTM D 2665)

Operating Temperature (°F) 73 80 90 100 110 120 130 140

Correction Factor 1.00 0.88 0.75 0.62 0.50 0.40 0.30 0.22

Pipe Stiffness 310 272.8 232.5 192.2 155 124 93 68.2

Using Cellular Core vs Solid Wall Pipe

Cellular, or foam, core PVC and ABS pipe is extruded with a layer of foam sandwiched

between inner and outer layers of solid plastic. Due to decreased pipe stiness and less

resistance to mechanical cleaning, some speciers nd cellular core PVC is not suited for

commercial applications. If cellular core pipe is used, speciers should conrm the material

installed is consistent with their specication and with the requirements of the application.

Buried pipe collapsed due to exposure to

excessive temperatures

Cellular core of PVC stained

orange for identication

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Installing PVC Pipe in Underground Applications Switching a commercial plumbing system from cast iron to plastic takes more than just changing materials. Installation requirements change, and failure to address these differences may result in your plumbing system failing. Key Points to Remember Incorrect Underground Installation Bedding and Backfill Proper bedding and backfill include digging a larger trench and taking extra care when installing the foundation and bedding.
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Mechanical Cleaning Unstable Soil Maintenance and drain cleaning to remove blockages are required to keep DWV systems performing optimally. This is especially true in hospitals, prisons, hotels or food service applications. Mechanical cleaning using auger bits or high pressure water may damage ABS or PVC pipe and fittings.