TECHNICAL
3. Supply demand – Reference section A 103.1
4. The minimum required residual pressure at the
highest fixture – Reference section A104.1
5. The elevation of the highest fixture – Reference
section A104.2
6. Pressure loss through the building supply line –
Reference section A105
7. Pressure loss though branches and risers –
Reference section A106
8. Pressure loss though fittings – Reference section
A107.3.
MATERIAL CONSIDERATIONS
Among the other factors that can impact pressure loss
calculations, are pipe materials. While CTS (copper tube
size), PEX, CPVC, and copper all have the same outside
diameters, the materials themselves require different wall
thicknesses to meet standardised pressure ratings, with
copper the thinnest, PEX the thickest, and CPVC in-between.
Therefore, for the same amount of water flowing, the
velocity and pressure loss will be greatest with a PEX system
due to its smaller internal diameter; a larger pipe size might
be required to maintain the necessary residual pressure
at the farthest fixture. The flexibility of PEX may reduce
the number of fittings versus CPVC, but the pressure drop
through a CPVC fitting is less than a comparable PEX fitting.
While CPVC and copper fittings surround the exterior of the
pipe, PEX fittings are inserts, which creates orifices in the
piping systems and restricts flow.
Copper can also experience some pressure drop over
time as it corrodes, and the surface becomes rougher.
This is calculated using the Hazen Williams C factor,
which is a constant that applies to the pipe related
to smoothness. Under the C factor, the higher the
number, the smoother the pipe. At their origin, steel
has a C factor of 120, and PEX, CPVC, and copper
150. However, copper’s number will decrease over
time as the material scales and corrodes; CPVC’s
number remains constant.
53
closing valve, such as a washing machine or an ice maker,
water goes from seven or so feet per second to zero in less
than a second. This creates a pressure wave in the pipe.
In general, the peak pressure wave should not exceed one-and-
a-half times the maximum operating pressure of the pipe that
is experiencing the pressure wave. The pipe should be properly
sized to avoid exceeding this limit. In some regions, water
hammer arrestors are required by code to absorb the pressure
wave before it travels down the pipe.
For these devices to be effective, they must be placed as
close to the quick-closing valve as possible. Even if the
pressure wave does not exceed one-and-a-half times the
maximum operating pressure, the wave can still create
unacceptable noise in the system. Pressure arrestors can be
used to dampen this noise.
UNDERSTANDING CPVC
CPVC is ideally suited for commercial applications, including
schools, office buildings, retail, and hospitals, as well as
industrial applications, including chemical processing,
manufacturing, mineral processing, wastewater treatment,
power generation, and marine applications.
CPVC is self-extinguishing and has relatively low smoke
generation. CPVC has a much higher limiting oxygen
index (LOI) value than many other common materials of
construction, and thus will not support combustion under
normal atmospheric conditions.
Performance-wise, CPVC is characterised as follows:
• Durable: CPVC plumbing systems will not pit, scale, or
corrode like metallic systems — regardless of water quality.
• Cost-efficient: A CPVC system costs less and is faster and
easier to install than traditional metal systems. No torches
required. Pipe and fitting are solvent-welded quickly
and firmly, and in the long term, the CPVC system offers
additional savings because it is highly energy efficient.
• Selection: Pipes and fittings up to 24 inches meet the
needs of nearly any commercial project.
Corzan CPVC’s online
design calculator
simplifies the sizing
process. Designers and
engineers simply input
the parameters of the
piping system, such
as pressure losses,
minimum daily service
pressure, and pipe
type, and the tool will
determine the allowable
friction loss, velocity,
and demand flow rate.
Another challenge is oversizing a pipe system. At times,
sizing tables do not offer the necessary granularity to
accurately size a system. When this is the case, it is best
practice to select a larger pipe size to ensure that required
demand is met with excess capacity. The result is greater
expense and wasted water, which is a growing concern
in many regions around the world. You can use a small
pipe and push water through very quickly, but it’s not
necessarily feasible. First is the potential for erosion in
copper pipes, which are generally limited to five linear feet
per second for hot water and 8–10 feet per second for hot
and cold, depending on the size of the pipe. Second is the
phenomenon of water hammer. For devices with a quick-
Continued on page 55 >>
www.plumbingafrica.co.za
March 2019 Volume 25 I Number 1