Le Toilet Page

Article by Sloan Flushmate

How 1.6 GPF Technologies Impact Today's Plumbing Conservation

	The Federal Energy Act and other water conservation trends are pushing fixture manufacturers to the limits of trying to achieve true water savings. It is the public's acceptance or non-acceptance of what "water savings" really means in terms of performance characteristics that is really the driving force behind the dramatic changes taking place in plumbing today. In fact, a new technology had to be developed in order to meet the demand for toilet performance. That technology is pressure-assist, and today, along with continued improvements in gravity-type toilets, it offers the public the best chance of reaching true water conservation without sacrificing performance.
	Toilet Manufacturing: an overview Once the decision to take a serious look at water consumption levels and water conservation was made, fixture manufacturers responded with only slight modifications in the gravity product design. A strategy was followed to shutoff the flush valve prematurely on existing water closets. By doing that, the objective of less water (1.6 GPF) would be used, achieving the water-conservation objective with minimum changes to the china fixture. What resulted, however, has contributed more to the negative impressions about 1.6 GPF (gallons per flush) low consumption toilets than any other factor. Simply, the concept of just minimizing the fixture changes didn't work. A general rule of fixtures that evolved from these failures might be: the larger the volume of water, the larger the raceways that can be accommodated in the toilet. Large amounts of water "use the room" as they travel through the china to deliver their energy; this energy takes advantage of large trapways and choke areas. However, when volumes of water are reduced without corresponding changes in the fixture, the larger raceway actually acts to dissipate the energy rather than deliver the energy. The lower volume of water quickly "uses up" its force along the large openings as it travels through the fixture. In many cases, the trapway's larger size on these early models actually prevented the siphon itself from forming during the flush. The result: terrible performance. Thousands of people, who never gave a second thought to toilet performance, started asking questions such as: Why do I have to double flush all of a sudden? Why am I holding down the handle longer to clear the bowl? Why do I have more clogging than before? Why does my toilet have to be cleaned more often than before? Manufacturers quickly realized that a re-design was essential...that the raceway size had to be significantly reduced to "re-capture" the force of the water. In other words, because the water in these early attempts was simply dying in the channels, low consumption - and ultimately water conservation - was getting the blame for poor performance.
	Change The fixture manufacturers responded with the design changes required. Figure One shows how a siphon wash works. The incoming rush of water comes through openings in the rim and acts like dumping a bucket of water into the bowl. A rapid filling of the trapway (1 1/2" minimum) triggers a siphoning action within the bowl, including the contents in the bowl. The action provides for a quick withdrawal of water from the bowl with minimum water rise. However, its characteristic small water surface area (6 x 8) makes it vulnerable to soiling and staining. To achieve low-consumption gravity performance, the size of the trap and other openings were decreased. This resulted in a stronger siphonic action to withdraw the waste, and much improved performance. Still, there was double flushing going on with gravity-only type models, and constant modifications are still being made to enhance performance (i.e., enlarge the trapway and water surface areas). It was about this time that pressure-assist technology made its appearance in response to the continued dis-satisfaction with the siphon-only action of early low consumption gravity models. From early efforts to simply utilize a gravity-type bowl with the pressure vessel, fixture manufacturers realized that like gravity, a new bowl design was essential to the success of pressure. A re-thinking of traditional models was required. In fact, the eventual design of a pressure bowl is the main reason that pressure-type technologies do not retrofit on existing toilets: they require specific design elements to accommodate the strong forces from pressure - elements that are not built into a gravity bowl.

For example, a pressure-assist fixture (Figure One) incorporates a pushing action instead of the siphon, specially designed to provide the force. Using a simplified trapway (2" minimum), the powerful force of pressure and water begins the flushing action instantly. The bowl must be designed to accept this force. The water surface area is also larger ( 116 sq. in.), helping keep the bowl cleaner.

FIGURE 1

Pressure is On From the early designs, component integration made today's pressure-assist technology responsible for delivering the performance that people have come to expect from toilets because it is performance that surpasses even the traditional "water guzzlers" of the past, only with a lot less water. Early use of pressure technology was limited to commercial applications, largely due to costs and a lack of awareness at the residential levels. Also, the "pressure flush" was slightly more noisy than what people were accustomed to in gravity water-guzzlers. Nevertheless, because of a public's expectations in toilet performance, and the fact that in some cases, gravity units do not meet those expectations, pressure-technology started to gain acceptance by the public in general. Today, pressure toilets have been installed in commercial, residential, institutional, industrial and virtually every type of building

Performance The best way to understand the differences between gravity and pressure technologies and subsequent performance is to compare it to automobiles and MPG. Before the oil embargo, American vehicles guzzled a lot of gas. When the embargo hit, manufacturers responded initially with vehicles that simply didn't perform: while they saved gas, it took an extraordinary time to accelerate to 50 MPH. They went back to the drawing board and developed better performance. The analogy holds true for toilets and GPF. Today, there are two technologies to chose from: pressure and gravity. In gravity technology, energy is exerted at a pattern-type flow as shown in Figure 2. There are two forces involved in the flush: water and gravity. The siphon action, as it gathers momentum, builds to a point of discharge.

Figure 2 also shows the typical pressure curve. There are three forces involved in the pressure flush: water, gravity AND pressure. By introducing pressure into the equation, the discharge levels are actually enhanced enormously. It can also be seen why earlier attempts to use a gravity-type vessel with pressure did not work: the gravity-type fixture was simply unable to deal with the forces created by the pressure flush.

FIGURE 2

	Discharge levels of 85% of water at a flow velocity over 70 GPM are typical of pressure, compared to gravity's 20 GPM averages. In other words, more happens with less water usage - which is what conservation is all about. And, it can be measured.
	New Performance Standards The ASME A112.19.2 Standards Committee has developed installation classifications for toilets, with a Bulk Load Test for each Classification. These classifications are: 1) Residential, 2) Transient (Hotels, Motels), 3) Commercial, and 4) Public. These tests are designed to distinguish the minimum extraction performance requirement for each classification. The next issue of the standard will spell out specific tests that fixture manufacturers must follow to measure performance, and may be of help to you in fixture selection. The new standard will also drop the drainline carry requirement for fixtures. While this is an interesting development, care must be exercised in weighing the pros and cons of WHERE the standard should be dropped (across the board, or only in specific situations). To illustrate, the toilet is part of a plumbing SYSTEM, and therefore, acts as a component in a system. It acts, and in turn is acted upon, by other components. Dropping the 40 ft. requirement in drainline carry will change the model that engineers use to calculate flow rates, pipe sizing, etc. This would have greatest impact on maintaining drainline carry in Class III and IV construction due to the lack of tributary water flowing upstream of the toilet outlet. In a Class I or II facility (residential home or hotel); there is enough tributary flow and water usage to keep waste moving along. Retaining the current drainline standard would therefore greatly reduce the likelihood of a drainline problem in Class III and IV construction. The bottom-line is that the standards MUST reflect the performance expectations of the public. It is only through such standards that the public can be assured that low flush toilets do, in fact, perform as intended.
	Do Low-Flush Toilets Work as Well as Regular Toilets? The short answer is "yes." The long answer is that "as well" differs from person to person. A recent survey of low-flush toilet users in a residential environment conducted by the Los Angeles Department of Water and Power in October, 1995, found that purchasers who participated in the rebate program were generally very satisfied with their low-flush toilet performance. They report satisfaction with these toilets to be "high," and that satisfaction relates directly to the frequency of problems that the public encountered with the new toilets compared to older models. Interestingly, the overall highest satisfaction ratings were given by respondents who reported that they double flushed less often than their conventional toilets, and by those who need to clean their toilets less often. The study also pointed out this: that there are significant differences in performance between brands and models of low-flush toilets as measured by the frequency that problems occurred. These differences related directly to overall purchaser satisfaction. Care, therefore, must be observed in low-flush recommendations (copies of the report available by writing to DWP, Box 111, Rm 1348, Los Angeles, CA 90051). Or, CLICK HERE

	The Changing Landscape San Simeon, California is a good example to understand some of the differences in these technologies and how they relate to low flushing. As the now-infamous western drought of 1986 continued, the effects on the city's water supplies grew more severe. Also, waste water treatment plant demand was reaching 100% capacity during the peak season. As the situation intensified despite a public awareness water conservation program, all outside water was banned in 1988. In 1989, with well levels becoming critical, a new action plan had to be decided upon. The choices were rather grim: new, supplemental water sources, additional waste treatment capacity, more rationing, including closing 10% of the motel rooms (the city depended on for tourism). The alternative that they finally settled on was replacing all toilets with low consumption types. After tests and evaluation between the technologies, pressure was selected because of the commercial successes it had experienced. Also, the administrators performed their own evaluation tests, and settled on pressure. The town decided to changeout all of the residential units as well. The additional "leverage" of pressure, according to the administrators, seemed to contribute to securing their chances for the best results. Once pressure-assist low consumption toilets were installed, water consumption in the town was reduced by 39% and bowl stoppages were reduced by 95% compared to the older 3.5 GPF toilets. Besides preserving the economic vitality of the community, the low consumption systems eliminated ALL double flushing. Such success has been multiplied since then in hundreds of situations like San Simeon. The performance of pressure in these situations has been unsurpassed, both in terms of water conservation AND in user satisfaction.
	How Much Water Is Really Saved? If a toilet is more than 15 years old, it uses between 5 and 7.5 gallons of water per flush (GPF). The older the toilet, the more water it probably uses. If a toilet was manufactured after 1980, it uses 3.5 gallons per flush, which is the current national standard( not considered a low-flush toilet). Studies performed in Massachusetts show that in an average 3.2 person household where each person flushes 4 times a day, a 7-GPF toilet uses 32,700 gallons of water a year. In the same household, a 5-GPF toilet uses 23,400 gallons of water per year; and a 3.5 GPF toilet uses 16,400 gallons per year. Studies done at various places around the country show that toilets account for anywhere from 35-42 percent of all indoor household use.
	You can see a series of checks that can be used in deciding between gravity and pressure technologies by linking to the Pressure Checklist above. Remember that each technology offers distinct advantages which depend on the specific application involved. It is safe to assume that gravity will be your first choice, unless the conditions exist that are on the checklist. If a condition does exist, then it will be worthwhile to consider pressure. For example, it is important to identify whether the project is residential or commercial, and is a remodeling or new construction job. There are distinct situations where one technology will be preferred over the other (i.e., when a user is dis-satisfied with the current toilet, pressure should be used). Evaluate the water supply, pressure levels involved. Then, examine the piping. Are they oversized for 1.6 GPF today? Have they been installed for a long period of time? Could there be bacteria buildup that would restrict low flow? Could there be reverse pitches or dips and valleys in the drain that would give a gravity-only force a difficult time? Such questions go a long way to helping you determine which technology fits best for the installation. Commercial applications require especially close evaluation. More and more states are mandating the use of pressure technology in commercial structures for a good reason: the average user in a public or semi-private area doesn't own the fixture and can put things in that fixture with no concern for what problems could be caused afterward. Pressure allows a building owner to deal with the unknown in a positive, "preventive" way. Besides giving commercial applications special consideration, it is important to evaluate the user(s) of the toilets. Are there children in the home? What are the needs for the size of adults in the home if residential? Will the commercial application be in constant usage? Evaluate the venting. In older systems, where vents could be restricted, back pressures can build up to unsafe levels. Asking and answering such questions give us a good way to evaluate whether gravity or pressure should be a consideration,

How Pressure Works Most people know how a gravity-type toilet works, and low-flush gravity units operate the same way. Pressure, on the other hand, is relatively new. Operation is as simple as gravity and begins as water enters the supply system and compresses entrapped air in the pressure vessel. When the toilet is flushed, the air reacts like a tightly-wound spring, surging the water out of the vessel at high velocity. The toilet bowl, which has been specifically designed to accept this flow of water, has a flush cycle of less than four seconds. The crest of the surging water easily pushes bowl contents through the drainline (see illustrations below).