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Does reduced flush volume have a negative effect on the performance in the drain line? World Plumbing Info reports on one manufacturer’s quest to find an answer.
The trend of reducing the volume of water used to flush sanitary fixtures is posing questions about drain-line performance. While fixture manufacturers focus on the performance of their products in the laboratory, what about the impact on the overall performance of the plumbing system?
Reduced-flow, single-flush toilets began to appear in Europe in the 1970s. Even then, water authorities around the globe raised concern about lowering the volume of the flush water used, when it was not known what effect such a reduction in quantity would have upon the flow within the associated drain lines.
In 1993, Australian sanitaryware manufacturer Caroma launched the first 6/3 dual-flush toilet, using just six litres for full flush and three litres for half-flush. This was the first instance when the technologies of both reduced-flush and variable-flush volumes were integrated.
Dr Stephen Cummings, manager of Caroma’s R&D department, has long held the view that, while the involved and exacting process of designing and manufacturing toilet suites is of paramount importance, a critical issue that needs to be considered is that the suite must be seen as part of a ‘balanced plumbing installation’.
CRITICAL DESIGN
“Much of the critical design and production process is based upon the need to retain as much of the energy of the flushing water for as long as possible within the pipeline system. This flow-transportation performance can be impeded easily if the drain lines taking the waste discharge from the toilet bowl are poorly or incorrectly installed.
“The construction of pipework with correct workmanship, gradient, true bore, smooth jointing and quality materials are all essential factors that will affect the overall performance significantly,” argues Dr Cummings. He initiated the design and construction of a pipeline test rig at the corporation’s Sydney manufacturing centre.
The elevated test platform, situated approximately four metres above ground level, allows toilet suites of various designs to be connected easily to 100 mm and 80 mm diameter drain lines. These clear plastic drain lines, extending for 60 metres and forming the longest test installation of its kind in the world, enable the test team to easily observe the waste-flow performance from up to five water closets set up on the rig, using varying drain-line grade configurations and low-flush discharges.
A number of intensive test programmes have been carried out over several years, incorporating national and international standards and procedures where applicable. The research programme provided valuable information regarding the flow and behaviour of waste through the toilet bowl and the drain line when using various low-flush discharge volumes.
By using various low-flush volumes, combined with the introduction of synthetic solids and toilet paper, the researchers gained valuable information and a better understanding of the performance criteria required to achieve a ‘balanced plumbing installation’.
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Test rig supports and pipeline hangers were designed and installed to replicate conditions experienced in the field. Initial gradients were achieved accurately by the use of a dumpy level, which proved to be very successful in achieving a continuous and correct gradient.
The researchers have even utilised current electronic levelling devices to obtain an easier and even more accurate process of levelling. While adjustment is labour-intensive, the rig will allow a variety of tests to be carried out at a number of gradients, while differing pipeline sizes and fitting conditions can also be tested.
In 2004, Caroma set a new benchmark for the industry when it introduced the first 4.5 litre/3 litre dual-flush toilet system. However, simply reducing the volume of water entering a cistern bowl can lead to certain problems.
REAL SCIENCE
The real science behind producing a reduced-flush performance toilet is in matching the flow of water from the cistern to the precisely-designed configuration of the toilet bowl. In one action, the flow from the cistern into the bowl needs to remove solids and paper, as well as cleanse the bowl, but even then, using ultra-low-flush volumes, the task is not complete.
The characteristics of the head of water exiting the trap and flowing down the drain line is critical to the long-term performance of the complete plumbing system. As Dr Cummings explains: “The key requirement between the WC and drain line is to fully discharge the waste from the bowl outlet using the initial part of the flush, and then to achieve steady flow conditions within a minimum distance within the drain-line system in order for the waste to clear the drain line effectively.”
Importantly, the performance levels observed on the testing rig were validated in trials in the field with existing drain line installations. Such trials emphasised one important task that cannot be neglected by any plumbing engineer or specifier, and that is to check the installation standards of contractors and staff regularly, as drain lines cannot be expected to be as forgiving when attached to low-flow fixtures. However, such perennial problems are global issues.
As societies come to grips with water as a scarce commodity, it is the responsibility of all to realise that, as the trade continually ‘pushes the boundaries’, there is a need to apply good and safe practices at all times if we are to achieve the goal of reducing our water consumption.
From the toilet cistern to the authorities’ sewer main, each component of the installation requires a ‘matched performance’ to ensure that adequate and continuous energy exists to provide an efficient and water-conserving solution to the increasing problem of water consumption.
For more information, visit www.worldplumbinginfo.com.
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