There has been a strong demand for global warming countermeasures and water resource conservation measures, and water-saving toilets have been promoted worldwide. However, while various types of water-saving toilets are commercially available, data about discharge characteristics of each type or variations in the characteristics when being connected to the horizontal drainpipe are insufficient, and basic unit data used in the steady flow rate method by SHASE-S 206 are unclear. Moreover, there is no systematic understanding about the results of carrying performance experiments involving the simultaneous draining of toilet paper, etc. Therefore, the collection and disclosure of basic data is required for plumbing design that involves the installation of water-saving toilets.
In response, the study examined fixture discharge characteristic values and carrying performance values by carrying out experiments. In the experiments, three water-saving toilet types; type I (low cistern system), type II (flushing valve system), and the common type, which are categorized by JIS A 5207-2014 'Sanitary Wares' according to the amount of flush water and the amount of drained water, were each connected to a fixture drainpipe (total length 16 m, pitch 1/100 and diameter 75A). Subsequently, the following knowledge has been acquired, which is useful for carrying performance and plumbing design.
(1)Compared to types I and II, the average drainpipe-connected fixture discharge rate,
qd', of the common type decreases gently and by a small amount along with the pipe length, and no significant difference is observed between type I and type II.
(2)Five types of experimental waste substitutes were used in the carrying performance experiment, and the results confirm that the common type ensures a carrying distance of 10 m or longer (with nine bends), and types I and II ensure 4-8 m (with 3-7 bends) when using toilet paper (layered) which is a realistic waste substitute.
(3)In each case of the five experimental waste substitutes, the relationship between the amount of flush water and the carrying distance has been clarified, and the approximate decrease in the carrying distance in line with the reduction of unit water quantity has been identified.
(4)The average drainpipe-connected fixture discharge rate,
qd', which serves as a carrying limit value, is approximately 0.3 L/s, which can be used as a standard value, and from the safety perspective, it is 0.5 L/s, which is roughly the same as
qd' for bathtubs. Therefore, in a plumbing design that ensures good carrying performance, plumbing conditions should be determined within the ranges of pipe lengths and numbers of bends so that the
qd' value is met at the end of the horizontal fixture branch.
The acquired knowledge helps to understand basic unit data about discharge characteristics of different types of commercially available water-saving toilets and carrying performance (carrying distances and the number of bends) through simulation using a plumbing model. Furthermore, the study achieved its objective in providing basic data of fixture discharge characteristics for use in the steady flow rate method stipulated by SHASE-S 206 while ensuring good performance of carrying waste when water-saving toilets are connected to drainpipes. The next study will examine carrying performance when using experimental waste substitutes which are approved for use in the current BL testing, and will discuss the possibility of predicting discharge characteristics of different types of water-saving toilets and carrying performance (e.g., carrying distances) by using a numerical simulation model.
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