User Guide

54 l uponorengineering.com
Reverse osmosis
and de-ionized water
systems
Reverse-osmosis systems and
systems using de-ionized water
for drinking water applications
are approved for use with
Uponor AquaPEX piping
granted the pH is between
5 and 8 and the maximum
temperature does not exceed
104ºF (40ºC). Uponor requires
the use of EP or stainless-steel
ttings with de-ionized and
reverse-osmosis water.
For process water applications
such as clean labs and other
industrial-type pure water
applications, please contact
Uponor for more information.
Surge pressure and
sound intensity
The main sources of sound
in a water piping system are
cavitation, surface roughness
and water hammer caused
by surge pressure. Typical
polymers will absorb sound
in the range of 10 dB/cm,
whereas metals are on the
order of 0.1 to 1.0 dB/cm. For
a given change in velocity, the
intensity of sound from copper
pipe will be higher than that of
PEX-a piping. Peak pressures
caused by a quick-acting
valve could be reduced by
18 percent to 40 percent by
utilizing Uponor PEX instead
of copper pipe.
When comparing the change
in sound intensity when
switching from copper to PEX
piping, with all else remaining
the same, the sound intensity
in the radial outward direction
is the primary area to evaluate.
Beginning with the general
wave equation
² p = (1/
c²)(M²p/M t²) and some
simplifying assumptions (e.g.,
point source of sound), the
relationship for intensity can
be derived with the following
formula:
I = pv
Where:
I = sound intensity
p = sound pressure
v = particle velocity
Water hammer
Water hammer is probably the
most signicant concern and
can be evaluated using the
following:
A = 4660 / [1+ kD/(Et)]½
Where:
A = Wave velocity
k = Bulk modulus of water
(300,000 psi)
D = Inside diameter of pipe
E = Tensile modulus of
pipe material
t = Wall thickness
For ½" nominal size piping, the
dimension ratio (D/t) of PEX
piping is approximately 7; it is
approximately 11 for copper
(Type K).
Assuming a PEX piping
modulus of 250,000 psi and
copper modulus of 16,000,000
psi, the wave velocity is:
PEX piping – 1,520 ft./sec.
Copper piping – 4,240 ft./sec.
The surge pressure is
calculated as P = Av/(2.31 g),
where v is the water velocity
prior to the valve closing and
g = 32.2. Assuming this is also
the sound pressure (i.e., no
losses), the sound intensity
can be calculated as: I = (A²)
(v)/74.4
For PEX piping, I = 31,000 (v)
For copper piping,
I = 242,000 (v)
This demonstrates that for a
given change in water velocity,
the intensity of the sound
from copper piping will be
approximately eight times that
of the PEX piping. While some
assumptions are made in
reaching this conclusion, even
a conservative estimate would
give copper piping a sound
intensity two to four times that
of PEX piping.
Water hammer
arrestors
When considering the need to
install water hammer arrestors,
there are two components
of water hammer that are of
signicance: surge pressure
and noise transmission.
The intent of water hammer
arrestors is to reduce the
surge pressure to 150 psi and
to minimize the amount of
noise transmission.
The International Plumbing
Code (IPC) and the Uniform
Plumbing Code (UPC)
both require water hammer
arrestors at quick-closing valve
locations. Tables 5-6 and
5-7 show surge pressure for
copper, chlorinated polyvinyl
chloride (CPVC) and PEX.
Pipe material Maximum measured pressure (psi)
Flow rate, gpm 2 2.5 3 4 6
½" Uponor PEX 136 150 169 193 244
½" PEX-b 143 168 177 212 274
½" CPVC 155 173 201 222 296
½" Type L Copper 194 239 266 318 422
Table 5-6: First peak pressure for each piping material and
ow rate (cold water)
1. Pressure response measurements include 60 psi static
pressure.
2. Closing speed of quick-acting valve estimated at 25
milliseconds.
3. Test performed at 54˚F/12.2°C (cold water temperature).
Surge Pressure in Plumbing Pipe Materials, PPI Report # 3285
Pipe material Maximum measured pressure (psi)
Flow rate, gpm 2 2.5 3 4 6
½" Uponor PEX 113 122 123 141 174
½" PEX-b 108 113 124 141 175
½" CPVC 142 157 174 203 252
½" Type L Copper 149 181 204 250 306
Table 5-7: First peak pressure for each piping material
and ow rate (hot water)
1. Pressure response measurements include 60 psi static
pressure.
2. Closing speed of quick-acting valve estimated at 25
milliseconds.
3. Test performed at 130˚F/54.4°C (hot water temperature).
Surge Pressure in Plumbing Pipe Materials, PPI Report # 3285
These tables show the surge pressure in Uponor PEX is about
38 percent less than the surge pressure in copper. The main
reason for the dramatic difference in these results is the exibility
of Uponor PEX piping. Because of its exibility, Uponor PEX
piping signicantly dampens surge pressure.