CSE_Bad_WCs by xiaohuicaicai


									          Why Many Low-Consumption WC‟s Don‟t Work?
There is no denying that plumbing fixture manufacturers have come a long way in helping stem
America‟s water shortage and waste treatment shortages. As the chart below depicts, the
consumption of the typical water closet in North America has plummeted by more than 80% from
around 7-1/2 gallons/flush back in the late „50s and early „60s, to what is now just starting to
emerge, 1.0 gpf.

The problem is that while these paper improvements look great, users will readily admit that actual
field performance has been anything but universally satisfactory.
                                      Typical WC Consumption/Flush


             [7.5 GPF]            92%

                                [5.5 GPF]


                                                    [3.5 GPF]



                                                                     [1.6 GPF]          17%

                                                                                      [1.0 GPF?]

               1960               1975               1985             1995              2005

Especially since the late 1970s, as severe droughts caused serious water shortages in the western
United States and inadequate waste disposal capability emerged in the east, there has been no
shortage of articles complaining about poor toilet performance. Desperate to find answers to these
social problems, Eastern authorities initially faced their problems by imposing construction
moratoriums in an attempt to balance waste disposal capacity with demand.

Because the toilet accounted for approximately 45% of all in-house water consumption, instead of
rationing, the western states took aim directly at the water closet. Spurred on by the great Fede ral
Government‟s success in legislating significantly better gas mileage [after the auto manufacturers
said it couldn‟t be done] bureaucrats appeared to be convinced that all they had to do to solve the
water shortage was legislate lower toilet consumption. Unfortunately, they didn‟t take time to verify
the new technologies, that they were mandating, really worked. The bureaucrats shrugged aside
manufacturer warnings and heard only what they wanted to hear. First they banned 5-1/2 GPF
WCs, and then, quickly followed by mandating 1.6 GPF versions.

For the most part, the early 3-1/2 gpf WCs were merely cut down versions of 5-1/2 GPF cousins.
The early 1.6 gpf versions were either direct imports from Europe or 3-1/2 gpf designs with less
Why Some Low-consumption Toilets Don‟t Work [Continued]
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storage water or partitions that restricted discharge volume. Soon, article after article and survey
after survey began reporting consumer dissatisfaction. The reason was simple, the “new” gravity
fed WCs didn‟t work anywhere like the old reliable 5-1.2 gpf versions.

To truly understand why these early toilets didn‟t work, we must step back to look at how the
historic gravity-flush water closet worked. Shown below is a “typical” gravity-activated, siphonic-
action water closet.

The gravity-activated, siphonic flush system uses the stored water’s weight to
generate flushing pressure. When the trip lever is depressed, it opens a flapper
valve. With the valve open, gravity pulls the fluid from the tank into the bowl and
through the S-shaped trapway. When the flow-rate through the trap reached a
critical rate, siphonic action is established [usually around 25 to 30 gallons/minute]
which then pull the bowl’s contents into the drain. The flush action continues until
the tank’s stored water is exhausted and the siphon is broken .

Looked at in a different way, the next chart below shows a typical [3-1/2 gpf] gravity-activated
WC‟s discharge profile in terms of discharge time versus flow water velocity. Siphon is not
obtained until after six seconds of flow, when this bowl reached approximately 20 gpm. In this bowl,
about 35% of its discharge was used to build siphon. Many 5-1/2 gpf designs were considerably
less inefficient – requiring as much as 75% of its stored water to establish siphon. All water used
before the siphon is established is wasted. None aids the extraction or the carry of waste in the
Why Some Low-consumption Toilets Don‟t Work [Continued]
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                 40.0               3-1/2 GPF Gravity Activated 2-Pc Combo.
                                                           Test Pressure = 20 psi [static]


    Flow (GPM)





                        0   1   2    3     4     5     6      7     8     9    10 11 12 13 14
                                                        Time (sec)

Coincidental with the arrival of the 1970s water shortages, was the introduction of the first new
toilet flushing technology in the 20th century, the flushometer-tank. Mansfield Plumbing was the
first fixture manufacturer to introduce this technology in the Quantum™ two-piece combination.
The Quantum incorporated a new [pressure-discharge] trapway design developed by Bert Preston.
The Preston trapway was fundamentally different from traditional bowl designs in that it had no
siphonic maintenance down-leg. Instead of restricting water flow to maintain the siphonic action,
the Preston trapway was designed to offer as little flow resistance as possible. Shown below is
Crane‟s pressure-assisted Economizer™ incorporating the Preston trapway design.
Why Some Low-consumption Toilets Don‟t Work [Continued]
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Another way of viewing the difference between a gravity-activate siphonic water closet discharge
and that of the pressure-assisted WC can be seen in the following chart which shows [compared
to the 3-1/2 gravity] that the pressure-assisted WC obtains a peak flow of 56 GPF [vs. 22.3] in less
than two seconds [vs. 6.5]. Its whole discharge is completed in approximately 3.3 seconds [vs
14.0]. Performance wise, the PA toilet‟s extraction was superior to the 3-1/2 gravity and
comparable to that obtained by the 5-1/2 GPF predecessors.
Why Some Low-consumption Toilets Don‟t Work [Continued]
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As more and more states jumped on the water conservation bandwagon, environmentalist
organizations were lobbying Congress for Federal legislation. While, initially, fixture manufacturers
opposed and successfully fought the first Federal legislative proposal, in 1991, they reversed
themselves when they decided they could more efficiently serve one Federal law rather than
[potentially] 50 different state requirements and threw their support to the environmentalist
movement. As a result, a “perfect storm” came together1 and the Federal Energy Efficiency Act
[“EPAct92”], which was already under review for updating appliance performance requirements,
was amended to include maximum shower head flow and water closet consumption. EPAct92
became law in 1992 with an implementation date [for showerheads and WCs] of January, 1994 in
order to allow manufacturers time to retool.

At the same time National Standards [upon which state and local codes mostly base their
requirements] were also undergoing a revolution. While historically, the Federal Government had
“effectively‟” set the national standard for toilets with their Federal purchasing specification WWP -
541[b], in the late „70s it decided to withdraw from that and let the private market sector determine
designs. This resulted in the emergence of the American National Standards Institute [“ANSI”] as
the dominating national standard-setting organization for water closets. The basic difference
between to two procedures was that industry ended up having a much stronger influence on the
standard development process for toilets under the ANSI system compared to when the Feds
controlled the system.

EPAct92 resulted in the most massive retooling ever experienced in the U.S. plumbing fixture
industry. In one swoop, seventy years of gravity-flow technology was scrapped in favor of an
unproven [1.6 gpf] concept. And as one might expect, the result of all this turmoil and change was
that unsatisfactory performing toilets were sold into the U.S. market for several years.

      In this writer‟s opinion, the water closet portion of the EPAct92 is flawed because it
      addressed only one aspect of the problem – total water consumption per flush. Extraction
      and drainline carry capability are not covered in the law. This omission allowed many
      unsatisfactory products to be released on the unknowing American public.

The following chart shows a comparison of the discharge [velocity vs. time] of a typical 3-1/2 gpf
versus a 1.6 gpf gravity toilet. As can be seen, the 1.6 WC‟s discharge velocity was at least 20%
lower than the 3-1/2 unit and 25% shorter in duration2.

1 It was interesting that the environmentalists only cited pressure-flush technology as their proof to those in Congress
that raised questions demanding to know where the proven 1.6 gpf technology was.
22 Since a 3-1/2 gpf WC‟s discharge was at least 20% lower than a 5-1/2 gpf, it is not surprising that the public was

dissatisfied with the 1.6 design. It was a significant come-down from a traditional water closet.
Why Some Low-consumption Toilets Don‟t Work [Continued]
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While market complaints were growing louder and louder, the fixture manufacturer dominated
ANSI Working Groups [where standard revisions start] actually pushed through several
simplifications. Their net result was to make it easier for a water closet to meet the standard‟s
minimum requirements. While several “public interest” [minority] members had wanted tougher
requirements and a rating system rather than the simple “pass/fail”, the fixture manufacturer
representative majority carried the day. While it made it easier for fixture manufacturers to get 1.6
designs certified, it certainly did not help allay the market‟s dismay.

One test in the ANSI A112.19.6 [Hydraulic Performance for Water Closets] standard that directly
related against proven 5-1/2 gpf capability is the drainline carry requirement3. It is that standard‟s
most controversial part. The manufacturer‟s has been trying to get that requirement eliminated for
several years because the test setup was cumbersome and time consuming. To pass, it also
requires the bowl‟s hydraulic design to be a compromise between its “thrust” [reasonable
discharge velocity] and its bulk extraction capability. For a given energy source, thrust varies
according to the bowl‟s trapway diameter – smaller diameter, more discharge velocity.
Unfortunately, reduced trapway diameters increased clog vulnerability. Thus, the drainline carry
test places the bowl designer in a dilemma – while larger trapways would reduce field [consumer]
complaints [less double-flushes and clogs] drainline carry would also be reduced.

3   The ANSI test requires a WC to equal at least 67% of the per for mance obtained by 5-1/2 GPF WCs.
Why Some Low-consumption Toilets Don‟t Work [Continued]
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         The argument has always been that waste, after it leaves the bowl, is not the bowl
         manufacturer‟s responsibility. The FM‟s maintain that is the waste system designer‟s
         job to plan a transport system that works.

Except for the American Society of Plumbing Engineers [“ASPE”] strong objection, the drainline
carry requirement would have been history many years ago.

While the market controversy regarding gravity activated 1.6 gpf toilets was raging, pressure -
assisted WCs were enjoying great market success -- because they worked. Users that had been
“frustrated” by unsatisfactory gravity 1.6 WCs started switching to pressure-assisted water closets.
And despite their considerably higher selling prices, by the end of 2002, PA toilets had gained
more than 15% of the overall market.

     Pressure-assisted water closets incorporate a flushometer-tank assembly within a
     conventional vitreous china enclosure. They use the supply system pressure to push
     water into a closed vessel. When empty, the vessel is full of air. Since air is almost
     perfectly elastic whereas water is not compressible, as the water is pushed in to the
     flushometer-tank‟s vessel, the trapped air becomes compressed. Water flows in until
     either the compression in the air equals the force pushing the water or the built-in
     pressure regulator shuts.

     When the trip-lever opens the flushometer-tank‟s actuator, an imbalance is created that
     causes the flush valve [“FV”] to lift. As the FV lifts, the compressed air in the unit‟s main
     vessel pushes the trapped water into the bowl at a high velocity causing extraction to be
     implemented almost immediately. Higher velocity of flow offsets the lower discharge
     volume [eg. 1.6 vs.3.5 gal.] so that a flushometer-tank activated WC‟s extraction
     performance matches that of the old reliable 5-1/2 gravity toilets of the „50s and ‟60s.

Because of their “turbo charge”, pressure-assisted WCs obtain a high peak discharge rate [50 to
70 gallons/minute]. Coupled with the Preston hydraulic bowl design, this high flow velocity allows
PA toilet combinations to match the extraction capability of the old 5-1/2 gpm designs.

Determined not to yield the market completely to pressure-assisted activation, one fixture
manufacturer introduced a vacuum-assist innovation - essentially the reverse of pressure-assist.
As the name implies, this double-trap design [as shown below] works by causing the initial
discharge to create a vacuum in the chamber located between the two traps. Thus the
atmospheric pressure on the bowl‟s well help inaugurate a siphonic flush action.
Why Some Low-consumption Toilets Don‟t Work [Continued]
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Gravity advocates weren‟t sitting back idly either. FM‟s quickly recognized that the Preston
trapway design was also better for a short 1.6 gpf gravity discharge. Incorporation of the Preston
trapway design coupled with a new [slot or open] rim design improved discharge velocity and thus
extraction performance.

One FM designer also rightfully reasoned that the 1.6 gpf WC‟s problem was insufficient peak
discharge velocity. He clearly reasoned that a larger bowl inlet would allow more water into the
bowl in a shorter interval, thus increasing the peak flow rate. As a result, the traditional 2” Douglas
flush-valve was increased to a nominal 3” diameter -- a 125% increase. This design change
increased the peak flow rate significantly and further improved the 1.6 GPF WC‟s extraction
capability, although still not matching the extraction performance of pressure-assisted WCs.
Unfortunately, the new 3” flapper type WC‟s costs have also escalated significantly so that these
improved WCs now cost more than pressure-assisted models4.

The following chart shows a comparison of the peak discharge velocity for the current state-of-the-
art in 1.6 gpf water closets in North America.

                                                                         Peak Discharge Comparison

                                    100.0                                                                   95.0
                                            VAC = Vacuum Assist
                                            2-G = Gravity w/2" Flapper
                                     90.0   3-G = Gravity w/3"flapper
                                            PF = Pressure-assisted


                   Flowrate [GPM]

                                     50.0                                      43.6




                                                     VAC                       2-G                   3-G    PF

4   Based on current retail prices at The Home Depot and Lowes super stores.
Why Some Low-consumption Toilets Don‟t Work [Continued]
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      The above numbers are discharges to air [eg. without any flow restriction].
      Flow rates through and out of a bowl are substantially lower because of friction, etc. What this
      data comparison shows is the performance opportunity potentially available to bowl designers.
      As bowl hydraulic designs continue to become more sophisticated, it is this writers view that
      1.0 gpf units are not far for general use.


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