Jun 13, 2002

Understanding High-Flow Valves

Luxury homes dominate the market trends for valves compatible with high-flow fixture demands

The demand for 11/4-inch plumbing in residential
applications is on the rise. Recent trends in new home construction have been
towards larger homes with more plumbing fixtures. Twenty years ago, a typical
home with 0.75-inch plumbing had two bathrooms, a kitchen sink, dishwasher,
laundry sink and two hard water outside hose bibs. Many new homes today utilize
1-inch (or larger) plumbing to supply three or more bathrooms, two kitchen
sinks, a bar sink, hot tub, laundry sink, mud room sink, soft water hose bib
and two hard-water hose bibs. While not all new homes include such luxuries,
the trend in even modest homes is toward including more fixtures and larger
plumbing piping.

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Already a Reality

According to Bruce Martin, industry expert and president of
W/C Technology, a MASCO company, larger supply pipes have been a reality for
years. ?Any credible plumbing contractor or architect will specify
plumbing supply lines and systems to meet the demands of the size of the
household, as well as its plumbing fixtures. Bigger homes with numerous
fixtures and higher water demand have led to the utilization of larger diameter
piping such as 11/4 inch. I?ve even seen cases where 2-inch
plumbing was used.?

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Flow Rates Predicted by Code

Providing a water conditioning system that meets the actual
water flow demands of new homes as well as the Plumbing Code requirements for
these homes is a challenge. Consider the requirements of meeting a strict
interpretation of the Uniform Plumbing Code 2000 Edition. The flow rates
required for a ?typical? home and a ?luxury? home are
shown in Table 1. The typical home in this example includes two and a half
baths, a kitchen sink, laundry sink, clothes washer and dishwasher. The luxury
home in this example includes three and a half baths, two kitchen sinks, a bar
sink, laundry sink, soft water hose bib, clothes washer and dish washer. These
are not atypical in today?s housing market, yet the flow rates required
by code are 19 gallons per minute (gpm) for the typical home and 24 gpm for the
luxury home.

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Observed Flow Rates

Given the high flow rates predicted by the codes, how has
the water conditioning industry been able to satisfy its customers? needs
when the vast majority of the systems sold today are not capable of providing
such high flow rates? The answer
is that when the fixture flow guidelines included in most plumbing codes are
strictly interpreted they predict unrealistically high flow rates.

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In March of 2001, the Water Quality Association issued a
report entitled, Analysis of Indoor Peak Demands in Single-Family Housing,
prepared by Aquacraft, Inc. Water Engineering and Management. The data was
collected from May 1996 through March 1998. Some of the study?s
highlights include

? There
were 12 sites in seven states/provinces and a total of 1,188 households in the

? Data
was taken in both summer (peak) and winter (off-peak) seasons.

? A
total of 28,015 days of data was accumulated.

? A
total of more than 1.9 million flow events were recorded.

? The
average house size was 1,800 to 2,000 sq. ft. (11 percent had less than 1,000
sq. ft., 22.6 percent had between 1,000 and 3,000 sq. ft.).

? Water
used outside the home (i.e., irrigation, swimming pool, etc.) was not included
in the study.

? The
average household in the study included 2.8 people (2.13 adults, 0.22 teenagers
and 0.45 children under 13).

? The
average house had 2.3 bathrooms.

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Analysis of the flow ?events? include

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95 percent were at 6 gpm or less

99 percent were at 7.5 gpm or less

99.9 percent were at 10 gpm or less

? 99.96
percent were at 12 gpm or less

? On
average, peak flow events exceeding 12 gpm would occur only once every 1.14
years per site.

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System Flow Ratings

The code requires that the maximum flow rate for a water conditioner
be at a pressure drop of 15 psid or less. Valve manufacturers typically rate
the flow rates of their valves as ?valve only.? Since the valve manufacturers do not
have control over the design and installation of the water softener, they
cannot predict the ?system flow.? Valve only flow ratings do not
include pressure drop due to resin, distribution system and accessories.

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While advertised system flows must be based on third-party
test results, it is interesting to note how the different system components
contribute to the overall system pressure drop. The calculations in Table 2
compare 1 and 2 cu. ft. softeners assembled with valves rated at 21 gpm and
valves rated at 27 gpm (flow rate for valve only at 15 psid).

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From Table 2 we find

? That
there is only a 1.1 to 2.0 gpm difference in system flow ratings between a
water softener constructed with a 21 gpm valve versus a 27 gpm valve.

? The
valve contributes as little as 27 percent of the total system pressure drop.

? For
smaller (1 cu. ft.) systems, the resin pressure drop exceeds the valve pressure

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Other things that have a significant impact on system flow
include resin selection (uniform particle, standard or fine mesh), type of
distributor, use of a gravel under bedding system and plumbing used in the

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For example, consider the effect of assembling a 1 cu. ft.
system (21 gpm valve) as above but with a fine slot distributor and no gravel
under the bedding. The fine slot distributor installed in a system with
standard mesh resin and no gravel has a pressure drop of 3.17 psid at 12 gpm.
This system design change would result in a system rating of 11.7 gpm at 15
psid. This is about the same change in system flow as assembling the system
with a 27 gpm valve.

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Recent trends in home construction and strict interpretation
of plumbing codes are forcing the water conditioning industry to offer systems
with higher flow ratings. While the need for higher flow rates in larger homes
is genuine, the actual flow rates that are encountered are likely to be less
than those predicted using the traditional fixture count method to calculate
flows. The system manufacturer needs to carefully consider all components used
to assemble the system when designing a water conditioner to meet a specific flow requirement.

About the author

Dave Averbeck is the director of engineering at Pentair
Water Treatment (PWT) since 1999. In 1978, Averbeck started his career in the
water treatment business. Prior to PWT he worked for Water Services, Inc. He
has a BS in mechanical engineering from the University of Wisconsin Milwaukee.