NZ250804A - A reduced volume cistern: increased static head of presssure - Google Patents

Description

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PATENTS FORM 5 PATENTS ACT 1953 COMPLETE SPECIFICATION Number Dated ^ 14 V £ \ 1994 'V <rO \P£\ V ..V' A CISTERN We, CAROMA INDUSTRIES LIMITEDj an Australian company, of 10 Market Street, Brisbane, Queensland 4000, Australia do hereby declare the invention for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement. ? 5 0 BO 4 -1a- The present Invention relates to cisterns and, 1n particular, to a reduced volume cistern.

For many years 1n Australia and other countries, cisterns (or flushing tanks as they are known 1n some countries) have been mounted to 5 the rear of, and generally slightly elevated 1n respect, to, the lavatory pan to which they were connected. The left to right dimensions of the cistern considerably exceeded the left to right dimensions of the lavatory pan. The Tatter's dimensions are essentially determined by the width of human hips and thus provide a standard reference for the 10 purposes of visual comparison. This reference applies not only to lavatory seats but to seating arrangements generally. As a consequence of this visual reference, a cistern 1s perceived in the mind of the general public to be an object which Is wider than the lavatory seat.

For many years in Australia the flushing volume used to flush 15 lavatory pans was approximately 11 litres. For some time the water supply authorities have been concerned to reduce the volume of water used by the general population as a means of deferring, perhaps even indefinitely, expenditure required for additional storage reservoirs. As a first step in this connection, dual button, dual flush cisterns 20 were introduced. With such cisterns, the "full" flush was set at approximately 9 litres, whilst the "half" flush was set at approximately 4.5 litres. This change 1n the maximum flushing volume was able to be accommodated without any substantial change In the overall configuration of the cistern.

However, the next step In the reduction of water consumption, is the introduction of dual flush cisterns in which the "full" flush volume is 6 litres and the "half" flushing volume is 3 litres. In addition to requiring changes In lavatory pan design, such a change also dictates a substantial change in overall cistern configuration since there 1s 30 little point in maintaining the overall cistern configuration 1f the interior capacity of the cistern is of the order of 11 litres, but the maximum flush volume to be discharged from the cistern is only 6 litres. Furthermore, 1f the overall size of the cistern can be reduced, savings can be made in material costs, freight costs, packaging costs, 35 warehouse storage volumes, and the like.

Accordingly, there are good technical reasons as to why a cistern with a changed configuration and overall smaller volume should be introduced. However, there are commercial dangers Inherent In such an HRW/17370 250 80 4 introduction since the purchasing patterns of the public may be changed when presented with a choice from an array of new cisterns from various manufacturers.

It is therefore an object of the present invention to provide a reduced volume cistern which will meet the necessary technical requirements but will also be commercially acceptable to consumers. Therefore, aesthetic considerations must be borne in mind in the overall design of the reduced volume cistern.

As mentioned previously, the width of the toilet seat represents a "reference" in aesthetic considerations. It has therefore been decided by the present applicant not to make the left to right exterior dimensions of the cistern smaller than the left to right dimension (or width) or a toilet seat. This decision was made because consumers were accustomed to cisterns being broader than toilet seats and a cistern which was narrower than a toilet seat might therefore appear "strange". Such a "strange" cistern could therefore have a limited market appeal.

In accordance with the present invention there is disclosed a cistern comprising a hollow, substantially rectangular, right prism having a left to right exterior: dimension substantially equal to the width of a toilet seat, wherein the rear wall of said cistern is provided with an internal volume reducing means to increase the static head of pressure of the reduced volume of flushing water able to be held within the cistern compared to the static head of said reduced volume of flushing water in the cistern without the volume reducing means.

A preferred embodiment of the present invention will now be described with reference to the drawings in which: Fig. 1 is a front perspective view of the cistern and toilet seat assembly of the preferred embodiment; Fig. 2 is an inverted plan view of the cistern and toilet seat assembly of Fig. 1; Fig. 3 is a plan view of the cistern and toilet seat assembly of Figs. 1 and 2; Fig. 4 is a side elevation showing how the cj^tet^iind toilet seat assembly of Fig. 1-3 are mounted on a lavatory pan in close coujfjRd fashion; c Fig. 5 is a rear view of the cistern of Figs.^^ ^y - - 2a - Fig. 6 is a plan view of the cistern of Figs. 1-5 wi showing by means of broken lines the equivalent dimensions of ? conventional toilet cistern; .f'i ii N f !( v, '■ *' \\ ;C ;X 2 5 OCT 7936 ;25 0 8 0 ;-3- ;F1g. 7 1s a schematic side elevation of the cistern of F1gs. 1-5 Illustrating the arc through which the float arm moves and Illustrating, by means of broken lines, the equivalent arc for a conventional cistern; ;Fig. 8 1s a plan view of the floor of the cistern of Figs. 1-5 5 showing the dimensions of the flush valve and, 1n broken lines, the dimensions of the floor of the conventional cistern; and ;Fig. 9 is a vertical front to rear sectional view through the cistern of Figs. 1-5. ;As seen in Figs. 1-4, 1n particular, the cistern 1 of the 10 preferred embodiment has a body 2 and a lid 3. The lid 3 1s provided with dual flush buttons 4, the front face of both the body 2 and lid 3 is generally concave so as to provide the "optical Illusion" of a comfortable backrest even though the back of the person sitting on a toilet never actually touches the cistern. This is for two reasons, 15 firstly since the lid 6 of the toilet seat assembly 6 Is Interposed between the back and the cistern, and secondly because the person 1s seated too far forward. ;As best seen 1n F1g. 3, the left to right dimensions of the cistern 1 are approximately equal to the width of the seat 7 of the 20 toilet seat assembly 5. The cistern body 2 has a rear wall 8 and a floor 9. The floor 9 contains an outlet 10 which 1s connected to an L-shaped flush pipe 11. ;As illustrated in Figs. 6 and 7, an initial consequence of deciding to make the left to right dimensions of the cistern 1 25 approximately equal to the width of the toilet seat 7, is that the conventional float arm 12 Is too long. ;Tables 1 and 2 provide comparative dimensional data in relation to both the cistern and the float mechanism from which 1t will be seen that the left to right dimension (or width) of the cistern 1 being set at 30 approximately 385mm (being the conventional width of a toilet seat) does not leave sufficient room for the conventional float arm 12 which has a radius of approximately 360mm. The action of the float arm 12 and float 13 is to close the inlet valve when the water level in the cistern has risen to the desired height. The pressure of the water inlet may vary 35 between 50 and 2000 kPa depending upon both the locality and the time of day. The shut-off pressure varies' 1n accordance with both the length of the float arm 12 and the buoyant force provided by the float 13. The buoyant force is itself determined by the float cross-sectional shape ;HRW/1737o ;25 0 80 4 ;-4- ;and the depth of immersion of the float which together determine the Immersed volume, since the float denlsy Is approximately constant and the weight of the float Itself 1s substantially Insignificant. ;From the foregoing 1t 1s desirable to have a float which 1s 5 relatively shallow 1n Its Immersed depth and which has a maximum „ horizontal, or plan, cross-sectional area. This is Indicated in relation to the conventional prior art float 13 In Figs. 6 and 7 since the reduced volume of the cistern 1 of the preferred embodiment dictates that the float geometry be changed. A relatively deep float (that 1s 10 one with a relatively small horizontal cross-sectional area but a substantial veritical extent) has the problem that for low inlet pressures the float tends to cut off the Inlet valve when the level of water 1n the cistern 1 1s relatively low. Conversely, with high inlet pressures such a float tends to allow in more water since Its buoyant 15 force Is less. This can lead to the problem that overflow may occur during the night as mains water pressure rises with increasing height in the local water reservoir as the volume of water in the reservoir 1s replenished during the low demand period which occurs at night. ;As will also be apparent from Fig. 7, a shorter float arm 14 1n 20 general leads to a bigger arc of travel for the same water level variation. It is also desirable that the inlet valve 16 which 1s located at the top of the inlet pipe 17, be open to a maximum extent when the inlet valve 16 is open, 1n order to ensure that the inlet valve 16 does not trap dirt or other debris which may be carried 1n the 25 incoming water. ;A further consideration is that the uppermost position of the float arm 14, determined by the Intended water level at which the cistern 1 is to be full, and the pressure of the mains supply, ;determines the height of the lid 3 and thus the maximum overall height 30 of the cistern 1. ;When al.l these considerations are taken into account, a larger float 15 (volume approximately 900 ml compared with 700 ml previously) but of more squat configuration and a substantially shorter float arm 12 were utilised 1n order to give approximately the same opening arc of 20°. 35 Naturally, the cistern 1 must also house the cistern operating mechanism 18. The preferred cistern operating mechanism 18.1s that described in Australian Patent No. 597438 (80111/87) and the dimensions ;HRW/1737o ;250 80 4 ;-5- ;of this arrangement set the minimum front to rear dimension at approximately 115 mn. ;As seen 1n Figs. 6 and 9, a bridge 20 extends across the r1m 21 of the cistern body 2 1n order to support the flush buttons 4 and their 5 associated mechanism 22. Since the cistern body 2 and lid 3 are preferably made from polypropylene which 1s flexible and relatively unstable dimensionally, the bridge 20 1s preferably made from ABS (acrylonitrile/butayd1ene/styrene) which is both rigid and dimensionally stable. Accordingly, the bridge 20 Imparts a greatly Increased rigidity 10 to the cistern 1. ;In addition to this advantage of the bridge 20, a further operational advantage has been achieved. In other cisterns provided with the abovemention cistern mechanism, in order to test the cisterns after their manufacture and prior to despatch, the cistern are loaded 15 into a test jig and the cistern filled with water. The the cistern mechanism was operated by a mechanism which replicated the flush buttons which were themselves previously mounted 1n the cistern 11d. ;Accordingly, occasionally the situation arose where a cistern would pass the test but the cumulative tolerances when the lid of the cistern was 20 placed in position, could result 1n the cistern mechanism not working properly. This was exacerbated If the lid was slightly out of tolerance. ;These problems are overcome 1n accordance with the cistern of the preferred embodiment since the buttons 4 are supported directly by the 25 bridge 14. Consequently, the cistern flushing mechanism can be tested by mechanical action applied directly to the buttons themselves during the in-factory testing procedures. ;The above arrangement results 1n a reduced dimension between the centre line of the outlet 10 of the cistern 1 and the front wall 19 of 30 the cistern. Consequently, this results in a change of dimension 1n the lever geometry of the operating levers 23 of the flush button mechanism 22 interconnecting the flush buttons 4 and the cistern mechanism 18. Preferably this 1s overcome by the use of shorter levers 23 but with the same length ratios. This ImpMes a bigger arc of movement in order to 35 achieve the same 11ft dimension. ;The reduced volume cistern 1 also has a reduced dimension between the rear wall 8 of the cistern 1 and the centre line of the outlet 10. Previously the flush valve was supported on the outlet pipe fitting ;HRW/17370 ;25 0 804 ;-6- ;itself. However, this required coupling fittings on the flush valve cover. In order to reduce the diameter of the flush valve, It was necessary to remove the coupling fittings from the flush valve cover. In order to correctly locate the flush valve 25, four locating pegs 26 5 are positioned on the floor 9 of the cistern body 2 1n order to correctly locate the flush valve 25 relative to the outlet 10. ;The final consideration 1s the static head of pressure available to the flushing water. The static head of pressure has a substantial influence upon the flushing performance since, In general, the greater 10 the static head the more effective a given volume of flushing water. Accordingly, the static head of pressure must not be lowered below a certain level less the effectiveness of the reduced flush volume be undermined. Naturally, the minimum static head arises in the situation of a close coupled, or low level, cistern as Indicated 1n F1g. 4. In 15 practice, the minimum static head which 1s satisfactory 1s found to be approximately 330 mm above the centre line of the horizontal leg of the flush pipe 11. This sets the lowest possible height for the maximum water level within the cistern 1. The maximum water level within the cistern 1 determines the static head of both the full flush and the half 20 flush since the cistern is full at the commencement of each of these flushing actions. ;The greatest possible height for the maximum water level within the cistern 1 1s determined by the overflow of the cistern which constitutes the top of the stem 28. In practice a safety margin of 25 approximately 30 mm below the top of the stem 28 1s allowed for the nominal greatest possible height for the maximum water level (1n order to allow for overfilling due to night-time increases in inlet pressure, for example). ;Even when all the above described volume reduction measures had 30 been implemented, It was found that the Interior volume of the cistern was, in effect, still too large since with the maximum flushing volume of 6 litres positioned within the cistern 1, the maximum or full water level was not higher than the abovementioned lowest possible height for the minimum static head. ;35 In order to overcome this difficulty, a volume reducing measure was required. This preferably takes the form of two vertically shaped scallops 30 formed in the rear wall 8 of the cistern 1. The scallops 30 provided some additional benefits over and above the volume reduction ;HRW/1737o ;2.0 u BU 4 ;-7- ;required to reach the desired full water level in that the scallops 30 form a stiffening corrugation which Increased the bending moment and hence the rigidity of the cistern body 2. In addition, the scallops 30 are able to be provided at a substantially negligible additional 5 material content and are able to be so arranged as to not substantially Increase the difficulty of removing the body 2 from the Injection moulding tool 1n which It 1s formed. ;The foregoing describes only one embodiment of the present Invention and modifications, obvious to those skilled 1n the art, can be 10 made thereto without departing from the scope of the present Invention. ;HRW/17370 ;-8- ;250 8 0 4 ;TABLE 1 - Cistern ;CONVENTIONAL ;NEW ;Flush Volume ;9/4.5 litre ;6/3 litre ;Width ;500 mm ;385 mm ;Front to Rear ;150 mm ;115 mm ;Overall Height ;420 mm ;413 mm ;Water Levels Full ;1/2 Flush Completion ;260 mm 160 mm ;231 mm 125 mm ;Minimum Static Head ;320 mm ;330 mm ;TABLE II ;- Float Mechanism ;CONVENTIONAL ;NEW ;Float Arm Radius ;360 mm ;250 mm ;Float Volume ;700 ml ;900 ml ;Float Arm Arc ;20° ;20° ;HRW/17370 *

Claims (10)

25 0804'

1. A reduced volume cistern comprising a hollow, substantially rectangular, right prism having a left to right exterior dimension substantially equal to the width of a toilet seat, wherein the rear wall of said cistern is provided with an internal volume reducing means to increase the static head of pressure of the reduced 5 volume of flushing water able to be held within the cistern compared to the static head of said reduced volume of flushing water in the cistern without the volume reducing means.

2. A cistern as claimed in claim 1 wherein said volume reducing means comprises at least one, substantially vertically extending, stiffening corrugation. io

3. A cistern as claimed in claim 2 wherein, the, or each, stiffening corrugation has a substantial horizontal extent and forms a scallop.

4. A cistern as claimed in any one of claims 1 to 3 wherein the left-to-right exterior dimension of said cistern is approximately 385mm.

5. A cistern as claimed in any one of claims 1 to 4 wherein the minimum 15 static head is approximately 330mm.

6. A cistern as claimed in any one of claims 1 to 5 and having a bridge extending between front and rear of said cistern and supporting at least one operating button operable to activate the cistern.

7. A cistern as claimed in claim 6 and having a lid forming the top of 20 said prism, said lid having an aperture therein for receiving said operating button(s).

8. A cistern as claimed in any one of claims 1 to 7 having an outlet, wherein a plurality of location lugs surround said outlet and centre a flush valve positioned above said outlet.

9. A cistern as claimed in any one of claims 1 to 7 having a float arm of 25 approximately 250mm length pivoted at one end thereof and pivotable in an arc of approximately 20°, the other end of said float arm having a float of volume approximately 900ml, said float arm being operable to open and close an inlet valve for said cistern. G?;:. c* .;

10. A reduced volume cifetern substantially as described with reference to;&CO;Attorneys for the applicant;30 the drawings.;G GREG WEST-WALKER*