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line round the bowl 25 mm below the rim with a watersoluble ink pen and measuring the total length of unwashed line after flushing. |
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7. Blotting paper test, to measure splashing from the bowl during a flush by placing a sheet of blotting paper over the WC bowl and either estimating the area of wetted paper or weighing the paper before and after flushing. |
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8. Transport test, using a 14.3 m length of 110 mm UPVC discharge pipe at a gradient of 1 in 80, connected to the WC. Transportation performance of a model solid, typically a halflength C2-type maternity pad, was monitored by recording its velocity profile along the pipe (Howarth et al., 1980). This test provides the basis for the definition of the required flush volume relative to length and gradient of drain prior to connection of discharge from other sanitary appliances. |
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With the omission of the flushing rim, it was necessary to develop an effective means of distributing the flush water around the bowl. A device termed a 'diverter bar' was developed with two slightly downward angled side slots, with the primary function of distributing cleansing water round the bowl, and a bottom jet to induce momentum transfer to solids in the trap. The diverter bar was connected via a sleeve to allow for different diameters of flush pipe. |
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The design criteria governing low-volume flush WC performance (n) are shown in Figure 13.1. The four parameters, trapseal volume (S), flush volume (F), trap-seal depth (h) and minimum trap passage clearance (w), can be functionally related as follows: |
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Uujamhan (1981) identified two dimensionless parameters, ns and nF, determining WC performance for solid or fluid contamination removal, respectively (Figure 13.2), which should be as low as possible. |
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Laboratory testing and development led to a final WC prototype termed the Mark III WC and a Mark VI diverter bar, finally appraised with a plastic cistern and a modified ceramic |
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