TECHNICAL
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Table 1
CPVC piping systems can be installed using one
of two methods: chemical joining or mechanical
joining. The chemical joining process, called
solvent welding, eliminates the need to use a
separate primer. Installers cut the pipe, clean the
pipe and fittings, apply solvent cement inside the
fitting socket, assemble the joint, and verify proper
installation. The science of solvent-welding, which
forms a chemical bond, ensures that a properly
installed fitting is the strongest part of the system.
Mechanical joining options consist of cutting
and grooving the pipe, then connecting pipe
sections with specialty fittings. Mechanical
joining options are especially ideal for
alterations or repairs, as they eliminate drying
time and shorten system downtime.
EXPANSION LOOPS
Another key component to designing pipe
systems is factoring in expansion loops. Like
all building materials, CPVC pipe materials
will expand when heated and contract when
cooled, and engineers must factor this into
the system design.
CPVC will expand about one inch per 50 feet
of length when subjected to a 50-degree
F temperature increase. Linear expansion
does not vary with pipe size. Expansion is
mainly a concern on hot-water lines; however,
expansion allowances for hot or cold water
pipe installed in unconditioned spaces should
account for the temperature difference
between the installed temperature and the
service temperature.
Expansion loop requirements for CPVC are
not much different than those of properly
designed copper systems. Generally, the
effects of expansion can be controlled
with changes in direction; an offset or loop
may be required on a long straight run.
One properly sized expansion loop (see
illustration) is all that is required in any
single straight run, but two or more smaller
expansion loops, properly sized, can be
utilised in a single straight run of pipe. Be
sure to hang pipe with smooth straps that
will not restrict movement, and remember
that the pipe must be free to move for the
expansion loops to work.
Table 1 shows calculated loop (offset)
lengths with ΔT of approximately 80
degrees F (90 degrees F to 170 degrees F)
based on diameter and length of two types
of CPVC pipe.
Per IAPMO IS 20, expansion loops are not
required in vertical risers, provided the
temperature change does not exceed 120
degrees F. Vertical piping must be supported
at each floor as specified by the design
engineer to allow for expansion/contraction,
and piping should have a mid-story guide.
Specify only hangers and straps that do not
distort, cut, or abrade the piping.
No matter the material or the project type,
consult with your pipe manufacturer for
special considerations and installation/
engineering requirements. PA
Tom Attenweiler is a product engineer for Lubrizol, while Don Townley is global codes and
approvals manager for Lubrizol.
www.plumbingafrica.co.za
March 2019 Volume 25 I Number 1