WO2010110744A1

WO2010110744A1 - An improved roof drainage outlet

Info

Publication number: WO2010110744A1
Application number: PCT/SG2010/000097
Authority: WO
Inventors: Chun Hee Goh; Kern Ling Yap; Gilbert Ang
Original assignee: Fast Flow Limited
Priority date: 2009-03-24
Filing date: 2010-03-17
Publication date: 2010-09-30
Also published as: SG165204A1; TW201114999A

Abstract

A drainage outlet device for positioning above a drain comprising a baffle of predetermined diameter D; a support arranged to support said baffle above the drain by a predetermined height H wherein a ratio of D:h is in the range 3.0 to 4.5.

Description

AN IMPROVED ROOF DRAINAGE OUTLET

Field of the Invention

The invention relates to devices and systems for the drainage of rainfall runoff from a roof. In particular, the invention relates to a drainage outlet device for use with a roof and in particular a gutter so as to maintain pressurized flow within the drainage system downpipes.

Background of the Invention

Roof drainage design can be broadly divided into 2 main categories

1) gravity flow - where the design principle is based on flow at atmospheric pressure.

2) pressurized flow - where the flow is subjected to greater positive or negative pressure than atmospheric pressure providing higher flow rates than gravity alone can provide.

In gravity flow, the pipework and in particular fittings are not designed to accommodate greater positive or negative pressure than atmospheric pressure. To ensure that excessive pressure is minimized, atmospheric pressure is maintained in the pipe limiting the fill rate of the pipes. In vertical rainwater downpipes, the maximum fill rate allowed is typically lower than 33% of the cross sectional area of the pipe. Rainwater from the roof or gutter flows towards the openings of a gravity rainwater downpipe with or without a dedicated rainwater roof outlet.

The absence of negative pressure in this category of drainage allows the use of non- pressure rated pipes and fittings, and so a marked reduction in cost compared to pressurized flow. The disadvantage is the reduction in capacity of such systems. Whilst useful for small roof catchments, and so forming the majority of all such domestic, larger roof catchments as experienced in industrial and commercial buildings require a higher flow rate, for the same rainfall recurrence period.

In pressurized flow, the height of water column within the pipework provides the necessary hydraulic head for transporting water through the pipework. In a low fill rate, non full bore condition, typically unstable conditions occur. There maybe a build up of water column from the bottom of the rainwater downpipe while the upper part of the rainwater downpipe may have flow patterns ranging from clear air-water separation that is gravity flow, part bore pressurised state of air and water, or unstable changes from one pattern to another. The basic design consideration is for the maintenance of a low and stable water depth in the gutters. Unstable conditions will lead to much higher water depths, and so flooding, or at lest make water depth unpredictable.

In a high fill rate situation the pipe is filled with water and the total height from the roof top to the discharge forms the hydraulic head of the system. The hydraulic head is at a maximum when the system operates under full bore condition; i.e. the pipes are fully filled with water. In general, pressurized flow produce higher flow rate than non- pressure gravity flow.

In conventional pressurised systems, designers aim for full bore flow, and so it is an important criterion to ensure that air does not enter the rainwater down pipe, so as to avoid unstable and unpredictable conditions.

In order to effect this the roof outlet fitted at the top end of the pipes is typically designed to prevent the entrance of air during high flow rate.

Accordingly such systems are designed with a degree of conservatism so as to ensure full bore flow is achieved at low flow rates or alternatively to have systems designed such that at low flow rates the system is large enough to operate as a gravity system. It is conventional wisdom that pressurised flow that is not full bore is unstable and difficult to predict. In fact of the three alternatives of:

(i) full bore pressurised: which involves complex and extensive engineering design calculations;

(ii) partial bore pressure: that is, two phase flow, and;

(iii) gravity.

Systems are developed to either fit into the first or last categories because of this unstable nature of partial bore flow, otherwise known as two phase flow.

It would therefore be advantageous if a system were developed that adopted pressurised flow but did not require complex and extensive design in order to achieve reliability. Alternatively, and possibly in combination, it would preferable to reduce the cost of design and potentially installation, without adversely affecting reliability.

Summary of Invention

In a first aspect the invention provides a drainage outlet device for positioning above a drain comprising a baffle of predetermined diameter D; a support arranged to support said baffle above the drain by a predetermined height H wherein a ratio of D:h is in the range 3.0 to 4.5.

In a second aspect the invention provides A drainage outlet device for positioning above a drain comprising a baffle for preventing water entering said drain from directly above said outlet device; supports form supporting the baffle above said drain so as to permit a flow of water to enter said drain and a turbulence inducer arranged to induce turbulence in the flow prior to draining into said drain.

Accordingly the system includes a drainage outlet device for placing over a drain which permits two phase flow under stable conditions. Conventional systems have not been designed so as to accommodate for or identify conditions which would allow for stable two phased flow with industry adopting the conservative view that two phased flow must be inherently unstable. Based upon the design of the drainage system according to the present invention, this instability occurs for only a portion of the range involved with a select range actually providing stable two phase flow. The baffle ratio is defined as the baffle diameter to the height at which the baffle is located above the drain. The present invention includes such a device having a baffle ratio in the range of 3.0 to 4.5.

In an alternative aspect of the invention, pressure fluctuation within the spigot assists in creating plug flow which induces pressurized two phase flow. Pressure fluctuation may be achieved by incorporating devices that causes turbulence within the device / spigot.

To this end, the invention also provides for a turbulence inducer, Such a turbulence inducer may be the incorporation of impediments to the flow, such as baffles or projections diverting flow around these impediments. Alternatively, the turbulence inducer may be an arrangement of the device in order to direct flow in a manner that leads to turbulence, such as against the formation of a Coriolis vortex. Alternatively the flow may be directed so as to promote asymmetry in the drainage of the water.

The device may be made from a single injection moulded member, of a suitable material including uPVC, HDPE. Alternatively, the device may be a modular assembly, whereby various members are assembled to form the device. In such a case, the device may comprise any one or a combination of uPVC, HDPE, galvanised or colour bond steel.

Brief Description of Drawings

It will be convenient to further describe the present invention with respect the accompanying drawings that illustrate possible arrangements of the invention. Other arrangements of the invention are possible and consequently, the particularity of the accompanying drawings is not to be understood as superseding the generality of the preceding description of the invention.

Figure 1 is an elevation view of a drainage outlet device according to one embodiment of the present invention;

Figure 2 is a sectional view of a drainage outlet device according to a further embodiment of the present invention;

Figure 3 is a sectional view of a drainage outlet device according to a further embodiment of the present invention;

Figures 4A and 4B are various views of a baffle according to one embodiment of the present invention;

Figures 5 A and 5B are various views of a base clamp according to a further embodiment of the present invention;

Figures 6A and 6B are various views of a spigot according to a further embodiment of the present invention;

Figure 7 shows various views of a drainage outlet device having a turbulence inducer according to one embodiment of the present invention; Figure 8 shows various views of a drainage outlet device having a turbulence inducer according to a further embodiment of the present invention;

Figure 9 shows various views of a drainage outlet device having a turbulence inducer according to a further embodiment of the present invention;

Figure 10 shows a characteristic of water depth against baffle ratio for a 77mm spigot, and;

Figure 11 shows a graph of water depth against baffle ration for a 103mm spigot.

Experimental Data

Experiments were conducted to determine the appropriate dimensional limitations on a drainage outlet device in order to achieve stable conditions for two phase flow. The tests were carried out using a modified version of the procedure ANSI/ASME A112.6.9 "Siphonic roof drains". The test involves providing a known flow from a basin into the drainage device which then directs the water through a down pipe. The down pipe was transparent so as to ensure two phase flow was developed within the down pipe. The water depth within the basin was measured along with the flow rate. Each test was conducted for a different drainage outlet device, having a variety of baffle ratios so as to determine stability of water depth for a particular range of baffle ratios. The tests were conducted for the commercially relevant diameters of 77mm and 103mm. The 77mm spigot was tested for typical flow rates of 6 litres per second, 10 1/s and 17 1/s, with the 103mm spigot tested for the flow rates of 10 1/s, 20 1/s and 33 1/s.

Table 1 shows the result of the test conducted for the 77mm spigot diameter with Figure 10 showing the graphed data.

Table 2 shows the result of the test conducted for the 103mm spigot diameter with Figure 11 showing the graphed data.

Stability is based on maintaining water depth for a range of flow rates. This is important as a significant change of water depth with a change in flow may lead to flooding of the drainage system leading to economic loss. For system designed for full bore flow, there will be a period at the commencement and end of the rain storm whereby Ml bore may not be possible through lack of priming of the system, but instead may fall into two phase flow or gravity flow, or oscillate between the two. It is here where conventional systems may be quite vulnerable to failure through flooding. It is therefore important to demonstrate that two phase flow is stable for a particular circumstance, even with change in flow rate.

Hence the object of the experiments was to determine the effect on water depth with a variation in flow rate and baffle ratio to in order to determine whether stability was possible. In each case, the water depth is found to be stable and consistent across the range of baffle ratios from 3.0 to 4.5, and substantially independent of flow. Above this range, the water depth markedly increases and is more sensitive to flow rate and baffle ratio. On the basis that sensitivity to change or dimensional variation of the drainage outlet device may have an adverse effect on stability, as compared to the range.

Detailed Description

The present invention includes a drainage outlet device for a pressurised drainage system. Unlike other systems the drainage outlet device according to the present invention is suitable for use with two phase flow. Conventional design avoids two phase flow on the basis that it is traditionally considered unstable, where stability is defined as the ability to maintain water depth at a predictable level for a particular water flow. This has not been contemplated previously as such stability was not considered possible.

The drainage outlet device according to the present invention provides for stable two phase flow when constructed within the specified range of baffle ratio of 3.0 to 4.5. The baffle ratio is defined as the diameter 35 of the baffle 25 divided by the height 40 at which the baffle is positioned above the outlet drain 11. It will be appreciated that the baffle may be of various shapes. In the case where the baffle is not circular, the dimension taken as "diameter" will refer to twice the distance from the edge of the baffle adjacent to the incoming flow to the centre line of the drain projected vertically through the baffle.

Figure 1 shows a simplistic representation of a drainage outlet device 5 positioned above a drain 11 ready for receiving an incoming flow 50. The baffle in conventional systems provides a protection against detritus falling into the drain 11 and so blocking flow down the downpipe 10. This is also the case with regard to the present invention. However, the baffle acts to restrict the volume of water entering the drain 10, and so not flood the gutter by incoming flow 50.

The baffle 25 is maintained at the required height 40 by a support 30, so that water flowing from the gutter 15 is free to flow 50 into the drain 10 and down the downpipe 11 in an efficient and stable manner as possible.

It will be appreciated that below the baffle ratio of 3.0 the baffle 25 may be of insufficient size 35, or the height 40 too great, to control the flow of water into the drain and therefore will become more easily flooded. Above the limit of 4.5, the baffle is too large to permit a sufficient amount of flow to drain from the gutter 15 and thus becomes unstable in providing drainage of said gutter. Key criteria in determining the success of a drainage device is the ability to maintain a consistent water depth for a specific flow. Thus instability is seen as the water depth increasing above a stable level.

Figures 2 and 3 show two alternative installations of a drainage outlet device 55, 95. In the first case shown in Figure 3, a spigot 77 has been mounted to a metal gutter 120. The baffle 60 and base clamp 65 have been press fit together to fit into the spigot 77 such that the device 95 is supported by contacting the lower surface of the metal gutter 120. Thus the device 95 substantially falls within the flow area of the gutter so as to receive the run off from the roof and direct this from the gutter into the downpipe 78.

The second alternative installation, as shown in Figure 2, is for a reinforced concrete (RC) gutter whereby a similar spigot 77 has been cast in place into the gutter 80. This may be an insitu cast in place if the concrete gutter is poured on site. Alternatively the gutter 80 may be cast as a unit and brought to site for mounting to the roof. In this case, the spigot 77 may be cast as part of a single construction unit.

To facilitate the installation of the device 55, a further bracket in the form of a clamping ring or annular cap 70 may be mounted to the spigot 77 so as to provide a consistent and level surface upon which the device 1 may be supported.

Based upon the installations shown in Figures 2 and 3, Figures 4, 5 and 6 shown key components of the drainage outlet device according to one embodiment of the present invention. Figures 4A and 4B show the baffle 60 comprising a disc 125 having fins 130 placed on a top surface.

The baffle 60 is mounted to a base clamp 65 which in this case is a press fit arrangement into toggles 145. The base clamp in this embodiment is generally circular in shape with the toggles on extended projections so as to appear in a flower type arrangement. The toggles 145 are formed into upstands 155 which are designed so as to provide the appropriate height for the drainage outlet device to achieve the desired baffle ratio based upon the diameter of the disc 125 of the baffle 60.

The clamp base 65 further includes a connector 165 formed into a downward projecting portion so as to fit with a spigot such as that shown in Figures 6 A and 6B. The downward projecting portion 160 includes a smooth but abrupt surface for directing the flow from a substantially horizontal direction in the gutter to a substantially downward direction for the downpipe. Figures 6A and 6B show a spigot used to facilitate the installation of the drainage outlet device. As is seen more clearly in Figures 2 and 3, the device fits within the spigot 77 to form the drainage outlet device. The baffle, such as that shown in Figures 4A and 4B engage the base clamp, such as the one shown in Figures 5 A and 5B, which engages the spigot 77 in a press fit arrangement for easy installation. Other means of fitting the device to the spigot 77 may be used including a screw thread arrangement (not shown) or a combination of these alternatives such as a rotational press fit such as a bayonet fitting (not shown).

Further still, the spigot 77 may merely provide a seat into which the baffle and base clamp can be glued or otherwise adhered.

The alternative arrangement whereby the device is merely fit within the gutter and downpipe may be achieved through a number of different means including construction glue, rivets screw fasteners and hot melt. The use of the spigot 77 by whichever means of mounting the device to the spigot 77, will further facilitate installation and so reduce the corresponding installation costs.

The spigot 77 may be installed at the same time as the guttering system for new construction ready to receive the device at a later stage. Alternatively the spigot 77 may be used a "retro fit" arrangement whereby an existing drainage system can be removed so as to install the adaptor. Accordingly the adaptor may be customised between new construction and retro fit so as to accommodate a standard device 1 and so reducing the overall number of parts required to be hold in storage.

It has been found that pressure fluctuation within the spigot assist in creating plug flow which induces pressurized two phase flow. To this end pressure fluctuation can be achieve by incorporating devices that causes turbulence within the device / spigot

The devices shown in Figures 2 and 3, and the device shown in the disassembled form in Figures 4,5 and 6 show a device with radial fins that directs the flow of water to collide in the centre of the device and thus creating turbulence and hence plug flow. By way of further, or alternative, example Figures 7, 8 and 9 show alternative embodiments of a turbulence inducer, arranged to induce turbulence.

Figure 7 shows one such drainage device 185 having one or more projections 195 projecting from the baffle downwards into the flow 200. The intention is for the water flow 200 to pass through into the device 185 and contact one or more of the projections 195 and so dissipate energy on contact with the projections forming greater turbulence within the device and so permitting lower energy flow into the drain 205.

Figure 8 shows a further alternative whereby a drainage device 210 having a baffle and a plurality of upstands 220 for supporting the baffle above the drain. In this embodiment the upstands 220 instead of being radially projecting and so allowing water to flow radially into the device, in this case the upstands 220 are angled. The angle is intended to be counter to the normal vortex formed from water draining. For instance for the northern hemisphere where a normal vortex may be counter clockwise, the upstands 220 may be angled so as to induce clockwise vortex and so resulting in turbulence within the device based upon the applied influences.

Figure 9 shows a further alternative embodiment whereby a drainage device 240 includes a baffle supported by a plurality of upstands 250. However, in this case the drainage device is arranged to be positioned off centre from the drain, and so promote asymmetry in the drainage of the water. Water entering the drainage device 240 and being directed radially into the centre of the drainage device will in fact not be positioned over the drain. The resulting flow will have a differential of one portion of the flow immediately entering the drain on entering the drainage device with another portion of the flow having to travel further before entering the drain, leading to asymmetrical flow or asymmetrical drainage. Once again the differential in flow induced by the drainage device will cause turbulence within the device and so producing a resulting drop in energy and a more efficient flow into the drain.

Claims

1. A drainage outlet device for positioning above a drain comprising a baffle of predetermined diameter D a support arranged to support said baffle above the drain by a predetermined height H wherein a ratio of D:h is in the range 3.0 to 4.5.

2. The drainage outlet device according to claim 1 wherein the ratio of D :h is in the range 3.0 to 4.0.

3. The drainage outlet device according to claim 1 or claim 2 wherein the ratio D:h is in the range 3.0 to 3.75.

4. The drainage outlet device according to any one of the preceding claims wherein said support includes a base clamp mountable to the baffle, said base clamp arranged to fit within the drain and mount to a spigot.

5. The drainage outlet device according to claim 4 wherein said device is an assembly of the baffle, base clamp and spigot.

6. The drainage outlet device according to claim 4 wherein said baffle and base clamp are moulded as a single unit.

7. A drainage outlet device for positioning above a drain comprising a baffle for preventing water entering said drain from directly above said outlet device; supports form supporting the baffle above said drain so as to permit a flow of water to enter said drain , and; a turbulence inducer arranged to induce turbulence in the flow prior to draining into said drain.

The device according to claim 7 wherein said turbulence inducer includes a plurality of projections projecting from an underside of said baffle and extending towards said drain wherein said projections are arranged to impede water flow entering said device.

The drainage device according to claim 7 wherein said turbulence inducer includes said supports arranged circumferentially about the baffle and angled such that the flow entering the device is guided by said supports to form a vortex in a direction different from a naturally formed vortex.

The device according to claim 7 wherein said support comprises a base clamp and a spigot wherein said baffle is mounted to said base clamp which in turn is mounted to a spigot so as to fit within the drain, said base clamp arranged to offset the baffle from a centreline of said drain.