AU2014202861B2 - A cistern - Google Patents

Abstract

A cistern (8) comprising a cistern tank (10), an overflow tube (16) and a cap (28). The cistern tank (10) has a predetermined maximum fill water level (14). The overflow tube (16) has an inlet (18), above the predetermined maximum water fill level (14), and an outlet (20). The cap (28) has a lowermost edge (30) spaced horizontally outwardly and vertically upwardly from the overflow tube inlet (18).

Description

1 A CISTERN Field of the Invention [0001] The present invention relates to a cistern for a toilet suite, and an outlet valve assembly for same. A cistern is referred to as a flush tank in the United States of America. [0002] The invention has been developed primarily for use with a gravity flushing (i.e. non siphonic) cistern and will be described hereinafter with reference to that application. Background of the Invention [0003] The use of an overflow tube in cisterns is known. The overflow tube allows water to escape from the cistern to the pan or floor in such a way as to not cause any flooding or back siphonage. Back-siphonage occurs when water from the cistern is drawn back into the mains water supply in response to a negative pressure being applied to the cistern inlet valve. For example, back-siphonage can be caused by a burst water main causing the water to drain out of a high rise building's plumbing system. Having the water level in the cistern rise above the top of the overflow tube during an overflow situation greatly increases the risk of back siphonage occurring. The regulatory bodies of many countries also require cisterns to have an air separation gap in the cistern, between the overflow spill level and any cistern openings, at the point of which back-siphonage could occur. However, such arrangements are undesirable as an overflow spill level that is considerably higher than the top of the overflow tube greatly increases the minimum height of the cistern and thus reduces installation applications. [0004] Known overflow tubes also rely on a large opening at their top, to maximise the flow rate of the overflow tube and thus minimise the overflow spill level. However, the outlet valve itself must also be designed to allow for a correspondingly high flow rate of water from the overflow tube to pass therethrough. This reduces design flexibility and can increase the minimum size of the outlet valve required.

2 [0005] Known cistern outlet valves also suffer from performance problems when operated in elevated installations (e.g. in ceilings). One such problem is a relatively rapid output flow rate causing the outlet valve to prematurely close. This premature closing is mainly due to two issues. Firstly, flushing water rushing up the inside of the overflow tube effectively forms a plug on to which the water leaving the cistern applies a negative (i.e. syphonic) pressure, which pulls the valve shut. Secondly, this water flow also displaces air from the tube that was acting as buoyancy for the valve and hence reduces the overall buoyancy of the valve, causing it to prematurely close. [0006] Another performance problem is air can be trapped in the flush pipe between the bottom of the cistern and the back of the pan during flushing. This air creates an airlock and restricts the flow rate of flushing water until the outlet valve closes and allows the trapped air out of the cistern. This causes a rapid pulse of water to be released at the end of the flush which creates splashing, noise and reduces pan clearance. [0007] Yet another performance problem of known outlet valves is they can produce gurgling noises during the latter stages of a flush due to air being sucked down the overflow tube and into the flush pipe, via a venturi effect. The gurgling noises are caused by water continually closing over and then re-opening the lower end of the overflow tube. [0008] To address the above issues, plumbers often need to use a series of different sized restrictors to restrict the flow rate through the outlet valve for different installation configurations. Whilst these can address some of the problems noted above, the restrictors also impact on overall pan clearance performance and require trial and error testing to ensure an optimal solution is found. Object of the Invention [0009] It is the object of the present invention to substantially overcome, or at least ameliorate, one or more of the above disadvantages.

3 Summary of the Invention [0010] Accordingly, in a first aspect, the present invention provides a cistern comprising: a cistern tank having a flushing outlet opening; an overflow tube having an upper end, open to atmosphere above the predetermined maximum fill water level, and a lower end; a flush pipe in fluid communication with the flushing outlet opening; an outlet valve operable to open or close the flushing outlet opening; an outlet tube beneath, and in fluid communication with, the outlet valve; and a breather tube having an upper end, in fluid communication with the overflow tube lower end, and a lower end extending into the outlet tube. [0011] The breather tube preferably extends into the outlet tube to at least an extent where substantially laminar flow develops in the outlet tube during flushing of the cistern. [0012] The breather tube lower end preferably extends into the outlet tube to at least an extent where an air pocket forms beneath the breather tube lower end that does not close over during flushing of the cistern. [0013] The breather tube lower end preferably extends into the outlet tube to at least an extent where the fluid flow through the outlet tube downstream of the breather tube lower end does not extend across the entire cross section of the outlet tube. [0014] The length of breather tube is preferably about 3-4 times the diameter of the outlet tube. The diameter of breather tube is preferably about 1/3rd the diameter of the outlet tube. [0015] The breather tube is preferably insertable within the overflow tube from the upper end of the overflow tube. The upper end of the overflow tube is preferably larger than the lower end of the overflow tube. The upper end of the overflow tube preferably engages the lower end of the overflow tube.

4 [0016] In a second aspect, the present invention provides a cistern outlet valve assembly comprising: an overflow tube having an upper end, open to atmosphere above a predetermined maximum nominal cistern water level, and a lower end; a flush pipe in fluid communication with a cistern flushing outlet opening; an outlet valve operable to open or close the flushing outlet opening; and a breather tube having an upper end, in fluid communication with the overflow tube lower end, and a lower end extending into a cistern outlet tube. Brief Description of the Drawings [0017] Preferred embodiments of the present invention will now be described, by way of examples only, with reference to the accompanying drawings wherein: [0018] Fig. 1 is a cross sectional front view of a first embodiment of a cistern, filled to its predetermined maximum nominal water level; [0019] Fig. 2 shows the cistern of Fig. 1 at the beginning of an overflow state; [0020] Fig. 3 shows the cistern of Fig. 1 during a siphon action created by the overflow state; [0021] Fig. 4 is a cross sectional front view of a second embodiment of a cistern, with a closed outlet valve; [0022] Fig. 5 shows the cistern of Fig. 4 after opening of the outlet valve; [0023] Fig. 6 shows a cistern similar to that shown in Fig. 4, but without a breather tube, after opening of an outlet valve; and [0024] Fig. 7 shows the cistern of Fig. 6 during mid flush.

5 Detailed Description of the Preferred Embodiments [0025] Fig. I to 3 show an embodiment of a cistern 8 with a tank 10. Fig. 1 shows the tank 10 filled with flushing water 12 to a pre-determined maximum nominal water level 14. An overflow tube 16, which has an upper inlet 18 and a lower outlet 20, is positioned within the tank 10. The bottom of the tank 10 has an outlet opening defined by a valve seat 21, which leads to an outlet spigot 22. The spigot 22 is connected to a flush pipe 24 via a reducer 25. The flush pipe 24 is connected to the mains sewerage via a toilet pan or urinal, as is well understood by persons skilled in the art. [0026] An outlet valve, indicated generally by the reference numeral 26, is positioned adjacent and above the spigot 22. The outlet valve 26 includes a float 26a, an outlet seal 26b and an outlet seal retaining nut 26c. [0027] The cistern 8 has a substantially cylindrical cap 28 with a lowermost edge 30. The edge 30 is spaced horizontally outwardly and vertically upwardly from the overflow tube inlet 18. Put another way, the lowermost edge 30 of the cap 28 is higher than the overflow tube inlet 18 and extends around the periphery of the overflow tube inlet 18. [0028] The operation of the cistern 8 during an overflow condition will now be described. As previously mentioned, Fig. 1 shows the cistern 8 filled with water to the maximum nominal level 14. With this amount of water in the tank 10, the overflow tube inlet 18 is higher than the water level 14. [0029] Fig. 2 shows the cistern 8 after the water level 14 has increased from the maximum nominal level and, as indicated by arrows 32, has commenced spilling over the overflow tube inlet 18 into the interior of the overflow tube 16 and then to the overflow tube outlet 20. The overflowing water then travels into the sewer main via the flush pipe 24 and pan or urinal. [0030] Fig. 3 shows the cistern 8 after the maximum flow capacity of the overflow tube 16 has been reached and the entire cross sectional area of the overflow tube 16 is filled with water. This creates a siphon within the tube 16. When this occurs, the cap 28 prevents air from entering the overflow tube 16 and breaking the siphon. The cap 28 thereby advatageously increases the flow capacity of the overflow tube 16 as it utilises the potential energy of the water leaving the overflow tube 16 to draw water from the tank 10 into the overflow tube 16 via the 6 siphon effect. For example, if the tank 10 is approximately 250mm deep with the cap 28 is positioned with its lowermost edge 30 5mm above the overflow tube inlet 18, there is 255mm of water head drawing water into the overflow tube 16. However, the same arrangement without the cap 28 will have only 5mm of water head feeding water into the overflow tube inlet 18. As a result, the capped arrangement is theoretically 50 times more efficient at draining the tank than a similar arrangement without the cap. This theoretical improvement is not achieved in practise due to other restrictions to the water flow. However, significant improvement is still achieved. [0031] The cap 28 also limits the spill level of the water flowing into the overflow tube 16 to only a level equal of that to the lowermost edge 30 of the cap, until the maximum syphoning capacity of the overflow tube 16 is reached. [0032] The cap 28 also provides several other advantages to the cistern 8. Firstly, the cap does not otherwise affect the flushing and refilling operations of the cistern. Secondly, the cap enables significant flow improvement in spill level performance due to the use of the syphon, which increases factors of safety and design. Thirdly, the cap reduces the spill level height above the top (i.e. inlet) of the overflow tube, enabling a more compact cistern design, thereby improving installation applications. Finally, the cap improves designer flexibility as it allows the use smaller overflow tubes with more flow restriction. [0033] A second embodiment of cistern 8' is shown in Figs. 4 to 7. Like components to that of the cistern shown in Figs. 1 to 3 are indicated with like reference numerals. The cistern 8' includes a breather tube 32 that has an upper end 34 in fluid communication with the overflow tube outlet 20 and a lower end 36 extending into the flush pipe 24. [0034] The operation of the cistern 8' during flushing shall now be described with reference to Figs. 4 and 5. Fig. 4 shows the tank 10 filled with water to the predetermined maximum nominal water level 14. To initiate a flush, buttons or a lever (not shown) are used to operate a lifter (also not shown) to lift the overflow tube 16. This also lifts the seal 26b off the valve seat 21. As shown in Fig. 5, this allows water to exit the tank 10 via the outet spigot 22 and the flush pipe 24. The air trapped in the float 26a provides buoyancy to hold the outlet valve 26 open. When the outlet valve 26 looses buoyancy, either due to the water level falling or due to some mechanical action, the outlet valve 26 falls and the seal 26b engages with the valve seat 21 to 7 stop the water flow. The cistern 8' is then refilled by an inlet valve (not shown) ready for another flush. This flushing operation is well understood by persons skilled in the art. [0035] As shown in Fig. 5, the lower end 36 of the breather tube 32 extends into the flush pipe 24, to an extent (depth) where laminar flow has already been established. This stops water from being able to flow back up the breather pipe 32, and the overflow pipe 16, and thus advantageously stops the premature closing problem previously discussed. [0036] Fig. 6 shows the equivalent situation (i.e. water flowing back up the overflow tube 16) which would occur in the absence of a breather tube. [0037] Further, the water flowing out of the tank 10 is accelerating due to gravity. As the water flow rate increases it therefore takes up a smaller cross-sectional area inside the flush pipe 24 and, as a result, air pocket 38 formed below the breather tube 32 never closes over. This allows air within the flush pipe 24 to exit through the overflow tube 16 and thus advantageously overcomes the airlock problem previously discussed. This results in a consistent flow rate throughout the entire flush. In addition, as the lower end 36 of the breather tube 32 is never completely closed over by water, the gurgling noise problem previously discussed also does not occur. [0038] Fig. 7 shows the equivalent situation (i.e. water closing over the lower end of the overflow tube 16) which would occur in the absence of a breather tube. [0039] Although the invention has been described with reference to preferred embodiments, it will be appreciated by persons skilled in the art that the invention can be embodied in many other forms. For example, the overflow tube, the cap and the breather tube need not be cylindrical and can be of any cross sectional shape.

Claims (10)

1. A cistern comprising: a cistern tank having a flushing outlet opening; an overflow tube having an upper end, open to atmosphere above the predetermined maximum fill water level, and a lower end; a flush pipe in fluid communication with the flushing outlet opening; an outlet valve operable to open or close the flushing outlet opening; an outlet tube beneath, and in fluid communication with, the outlet valve; and a breather tube having an upper end, in fluid communication with the overflow tube lower end, and a lower end extending into the outlet tube.

2. The cistern as claimed in claim 1, wherein the breather tube extends into the outlet tube to at least an extent where substantially laminar flow develops in the outlet tube during flushing of the cistern.

3. The cistern as claimed in claim 1, wherein the breather tube lower end extends into the outlet tube to at least an extent where an air pocket forms beneath the breather tube lower end that does not close over during flushing of the cistern.

4. The cistern as claimed in claim 1, wherein the breather tube lower end extends into the outlet tube to at least an extent where the fluid flow through the outlet tube downstream of the breather tube lower end does not extend across the entire cross section of the outlet tube.

5. The cistern as claimed in any one of claims I to 4, wherein the length of breather tube is about 3 to 4 times the diameter of the outlet tube.

6. The cistern as claimed in any one of claims I to 5, wherein the diameter of breather tube is about 1/3rd the diameter of the outlet tube.

7. The cistern as claimed in any one of claims 1 to 6, wherein the breather tube is insertable within the overflow tube from the upper end of the overflow tube.

8. The cistern as claimed in any one of claims I to 7, wherein the upper end of the overflow tube is larger than the lower end of the overflow tube. 9

9. The cistern as claimed in any one of claims I to 8, wherein the upper end of the overflow tube engages the lower end of the overflow tube.

10. A cistern outlet valve assembly comprising: an overflow tube having an upper end, open to atmosphere above a predetermined maximum nominal cistern water level, and a lower end; a flush pipe in fluid communication with a cistern flushing outlet opening; an outlet valve operable to open or close the flushing outlet opening; and a breather tube having an upper end, in fluid communication with the overflow tube lower end, and a lower end extending into a cistern outlet tube. Caroma Industries Limited Patent Attorneys for the Applicant SPRUSON & FERGUSON