WO2004018795A1

WO2004018795A1 - Drainage system

Info

Publication number: WO2004018795A1
Application number: PCT/GB2003/003495
Authority: WO
Inventors: David Paul Campbell
Original assignee: Heriot-Watt University
Priority date: 2002-08-23
Filing date: 2003-08-11
Publication date: 2004-03-04
Also published as: EP1540107A1; GB0219636D0; AU2003255782A1

Abstract

The present invention relates to a siphonic apparatus (1), for draining liquid, particularly for draining rainwater, off a roof (2), comprising a plurality of tubular members (4, 6). Each tubular member (4,6) has an inlet opening (8,10) arranged to be disposed at a different height relative to another opening. As the precipitation increases the tubular members with inlet openings located at the lowest level will reach their maximum capacity beyond which point liquid can be drained through the tubular members which have inlet openings positioned at sequentially increased distances above the inlet of the tubular members which are working at their maximum capacity.

Description

DRAINAGE SYSTEM

The present invention relates to the field of liquid drainage and more specifically to siphonic liquid drainage.

Drainage systems for roofs can be classified as conventional roof drainage systems, which drain precipitation from the roof under the action of gravity, or siphonic drainage systems. The down-pipes of conventional systems are sized and installed so that they operate less than 20% full of water at storm capacity. This inefficient drainage system can result in a large number of down-pipes being required, especially when large areas of roof are to be drained. Where such down-pipes are located externally on a building this impacts on the exterior design of the building and the need for large numbers of down-pipes adds to construction costs.

Siphonic roof drainage systems operate with down-pipes running 100% full, and can achieve many times the capacity of conventional systems, thus reducing the impact on the exterior design as fewer down-pipes are required for a given roof area and reducing the material requirements significantly. When a siphonic system is operating properly, with the pipes flowing 100% full of water the system only operates at one flow rate (the maximum) , which is dictated by the friction of the system itself.

Both conventional and siphonic systems are sized by considering the storm precipitation rates and roof area to be drained. Storm precipitation rates are obtained from statistical tables and, for most locations globally, the storm precipitation rates will be in excess of typical average precipitation rates by a factor of 4 or more. Storms are also likely to occur with a frequency that is only a few percent of that which typical precipitation rates will occur - but it is the storm rate that dictates the system parameters.

This variation in precipitation rate between the storm rate and the average rate causes problems for siphonic drainage systems. When precipitation rates are below the storm capacity the systems hunt between siphonic flow and non- siphonic flow such that a system may work very inefficiently and precipitation is drained from the roof at a reduced rate, causing water to pool on the roof. If precipitation falls above the storm level for which the system is designed the roof floods as the maximum capacity of the system has been exceeded. Furthermore, fluctuations or cycling in the roof load on the structure of the roof, as water pools and is then drained away by siphonic action, is undesirable and should be avoided.

In addition to the disadvantages associated with the inefficient operation of the system, when a siphonic system is hunting between siphonic flow and non-siphonic flow it can be extremely noisy.

A further known problem associated with siphonic drainage systems is the implosion of pipes due to air pockets forming within the pipes. Present attempts to overcome this problem rely on the use of pipes made from stronger materials which have increased structural resistance and integrity, but this adds to construction costs.

It is an object of the present invention to avoid or minimise one or more of the above disadvantages. In one aspect according to the present invention there is provided a siphonic apparatus for draining liquid, the apparatus comprising a plurality of tubular members, wherein each tubular member has an inlet opening arranged to be disposed at a different height relative to another opening.

Thus, by providing inlet openings arranged at different heights, liquid may be drained by siphonic flow over a wider range of flow rates, or precipitation levels. As the precipitation rate increases the tubular members with inlet openings located at the lowest level will reach their maximum capacity beyond which point liquid can be drained through the tubular members which have inlet openings positioned at sequentially increased distances above the inlet of the tubular members which are working at their maximum capacity.

It will be appreciated that the siphonic apparatus of the present invention is of use in the drainage of roofs, in particular of roofs which are generally known as "flat roofs". The siphonic apparatus may also be used for other applications including, but not limited to, for example, the drainage of ground surfaces from which liquid is to be drained, such as shower areas at swimming baths, pavements, streets, sports grounds etc.

Preferably, the tubular members are disposed in close proximity to one another. The tubular members may be adjacent one another, or may be disposed one within another. More preferably the tubular members are arranged coaxially. A coaxial arrangement of tubular members reduces the number of apertures required in the surface to be drained to accommodate the plurality of tubular members. Where the apparatus is used to drain a roof this simplifies construction of the building.

The tubular members may take any appropriate form, and are preferably of circular section. The tubular members may be one piece, or may be of sectional construction.

Preferably, the opening of each tubular member coincides to the flow area of the respective tubular member.

Preferably, the tubular member having the lowermost opening defines a relatively small flow area. Preferably, the flow area of the tubular members increases as the height of the inlet openings of the tubular members increases. Where the tubular members are arranged coaxially preferably the outermost tubular member will have the smallest flow capacity or volume through which water can be drained. It will be appreciated that the size of the flow areas and the difference in size of flow areas of the tubular members will be determined by the rainfall intensity, rainfall pattern and roof geometry, where the apparatus is used to drain a roof. Typically the size of the flow area reflects the flow capacity of the tubular members .

Preferably, the apparatus further includes fixing means for fixing the tubular members relative to one another. The fixing means may take any appropriate form, including screws, bolts, nails, adhesive, or the like. By fixing the tubular member to each other the tubular members may be further strengthened and the risk of implosion of the tubular members reduced. The fixing means may be adjustable to, for example, vary the relative heights of the inlet openings. Preferably, the apparatus includes at least one sliding collar disposed around the inlet of at least one tubular member to allow the height of the tubular member to be raised or lowered according to operational requirements.

Preferably, the apparatus further includes means for coupling the tubular members relative to a surface to be drained. The means for coupling may include screws, bolts, nails, adhesives or the like.

Preferably, the apparatus further includes baffle means for restricting or limiting swirling of liquid flowing into the tubular members . The baffle means may include one or more vanes. In a particular preferred from the apparatus includes an anti-vortex plate. The anti-vortex plate may be of any suitable geometry known in the art. For example, the plate could have a simple planar geometry, alternatively the anti-vortex plate could have a downwardly disposed conical shape. Where the apparatus comprises tubular members that are arranged coaxially, preferably the innermost tubular member of the coaxial arrangement is provided with an anti-vortex plate.

Preferably, the apparatus further includes a cover means for restricting access of foreign bodies to the inlet openings. The cover means may also serve as a baffle.

It will be appreciated that the capacity of the tubular members and the height of the inlet openings of the tubular members above the surface to be drained and their relative separation will depend on the amount of liquid to be drained at any one time, and the variation in drainage requirement over time. Appropriate apparatus according to the present invention can be designed to satisfy a wide range of drainage requirements and the number of tubular members, their capacity and the relative vertical separation distances of the inlet openings required can be readily ascertained by consulting climatic records/databases and known roof design parameters.

According to a second aspect of the present invention there is provided a building structure having a surface and a siphonic apparatus for draining liquid from the surface, the apparatus comprising a plurality of tubular members, wherein each tubular member has an inlet opening arranged to be disposed at a different height relative to another opening.

According to a third aspect of the present invention there is provided a method of siphonically draining liquid from a surface, the method comprising: providing a plurality of tubular members each having an inlet opening; locating the inlet openings adjacent the surface, and arranging said openings at a different height relative to the surface.

According to a fourth aspect of the present invention there is provided a method of siphonically draining liquid from a surface, the method comprising: arranging inlet openings of a plurality of tubular members adjacent the surface, and arranging said openings at a different height relative to the surface such that siphonic flow will occur in the tubular members in sequence.

Further preferred features and advantages of the invention will appear from the following detailed description given by way of example of some preferred embodiments illustrated with reference to the accompanying drawings in which:- Fig. 1 is a cross section of a siphonic apparatus according to the present invention;

Fig. 2 is a cross section showing the arrangement of tubular members of an apparatus according to an alternative embodiment of the present invention;

Fig. 3 is a perspective view showing the arrangement of tubular members of an apparatus according to a further embodiment of the present invention; and

Figs. 4 and 5 show a nomogram for design of a siphonic roof drainage system according to the present invention.

A siphonic drainage apparatus, generally indicated by reference number 1, for draining rainwater (precipitation) from a flat roof surface 2, is shown in Fig. 1. The drainage apparatus 1 comprises a first inner 4 and second outer 6 pipe of circular cross section which are arranged coaxially. The inner pipe 4 has an inner pipe inlet opening 8 which is at a higher level than the outer pipe inlet opening 10.

The roof 2 has a recess which defines a trough 11 within which the apparatus 1 is situated and within which water can pool. Rainwater falling on the roof 2 is channelled into the trough 11 to be drained by the apparatus 1. The apparatus 1 passes through a aperture 12 of circular cross section in the roof 13 such that a water tight seal is formed between the inner surface of the roof aperture 14 and the outer surface of the outer pipe 15.

The outer wall 16 of the inner pipe 4 and inner wall 18 of the outer pipe 6 define an annular channel 20 through which rainwater entering the outer pipe inlet opening 10 can flow. As the outer pipe inlet opening 10 is closer to the base 22 of the trough 11 than the inner pipe inlet opening

8 rainwater will initially be drained through the annular channel 20. During heavy downpours or storms the maximum capacity of water that can flow through the annular channel 20 will be reached causing the level of rainwater collecting in the trough 11 to pool and rise to a level high enough for water to enter the inner pipe 4 via the inner pipe inlet opening 8.

The inner pipe 4 is provided with a collar 24 of circular cross section which fits over the upper end portion 26 of the inner pipe 4. The inner pipe inlet opening 8 is defined by the upper open end 28 of the collar 24. The collar 24 can be slid vertically along the upper end portion 26 of the inner pipe 4, thereby altering the height of the inner pipe inlet opening 8 above the surface where rainwater collects 22 and the outer pipe inlet opening 10. The height of the collar 24, and hence the upper open end of the collar 28, relative to the inner pipe 4 can be adjusted by means of a threaded rod 30 which passes vertically through an inner pipe anti-vortex plate 32 situated above the collar 24. The anti-vortex plate 32 acts as a baffle. The anti-vortex plate 32 is anchored to the inner wall 34 of the collar 24 via rectangular support vanes 36 and has a central, downwardly disposed conical section 37. The support vanes 36 are in the form of blocks which are anchored to the collar 24 by a securing peg (not shown) .

The outer pipe 10 is also provided with a baffle in the form of an anti-vortex plate 38 which is anchored to the inner wall 18 of the outer pipe 6 via outer pipe vanes 40 which are secured to the outer pipe anti-vortex plate 38. The outer pipe anti-vortex plate 38 is similar to the inner pipe anti-vortex plate 32 but has a central aperture 42 to accommodate the collar 24 of the inner pipe 4 and hence the conical section of the outer pipe anti-vortex plate 37 is absent. The outer pipe vanes 40 are also coupled to the base of the trough 22.

The apparatus is provided with a filter 44 having a honeycomb shape which extends around the apparatus. The filter 44 is secured to the flat surface of the roof 2 in close proximity to the trough 11 and extends vertically to a height 125% of the height of the top of the inner pipe anti-vortex plate 32 above the base of the trough 22. The filter helps to prevent swirling of the rainwater as it enters the trough 11 and inlet openings of the pipes 8, 10.

The inner and outer pipes 4, 6 are fixed together by bolts 46. Sets of bolts are used to fix the pipes 4, 6 with respect to each other at positions spaced apart along the length of the pipes. Each set of bolts comprises 3 bolts each of which is positioned around the pipes' circumference 120° apart. The sets of bolts can, therefore, also be used to centre the inner pipe 4 within the outer pipe 6.

The inner and outer pipes 4, 6 are made of polyvinyl chloride (PVC) . The outer pipe 6 has an inner diameter of 91mm and the inner pipe 4 has an inner diameter of 63mm. The outer pipe inlet opening 10 is situated 100mm above the base of the trough 22 and the inner pipe inlet opening 8 is situated 25mm above the outer pipe inlet opening 10, although as described above by vertically adjusting the position of the collar 24 the height of the inner tube inlet opening 8 can be altered. These pipe dimensions and the position of the inlet openings have been found to be suitable for draining rainfall in Central Eastern Scotland including Edinburgh and the Lothians . Suitable dimensions for different climatic conditions and roof sizes can be readily ascertained and an appropriate apparatus designed.

In Figs. 2 and 3 alternative embodiments of the present invention are shown in which the detail of the upper end of the pipes has been omitted for clarity. In both Fig. 2 and Fig. 3 the drainage apparatuses 1' are situated within a trough 14 similar to that shown in Fig. 1 such that all the inlet openings of the pipes are positioned below the level of the flat surface of the roof 2 to avoid water pooling on the roof surface 2. In Fig. 2 four pipes 52, 54, 56, 58 each of different height are shown arranged in a line adjacent to one another, sequentially in order of increasing height. Each pipe has an inlet opening 60, 62, 64, 66 at the upper end of the pipes. The shortest pipe 52 has its inlet opening 60 positioned level with the surface of the base of the trough 22. The inlet opening 62 of pipe 54 is positioned above inlet opening 60; the inlet opening 64 of pipe 56 is positioned above inlet opening 62 and the inlet opening 66 of pipe 58 is positioned above inlet opening 64.

In Fig. 3 three pipes 68, 70, 72, each of different height are shown arranged in a bundle formation. The pipes 72, 70, 68 have inlet openings 78, 76, 74, respectively, positioned sequentially one below the other such that water drains though the lowest inlet 78 of pipe 68, then through inlet 76 of pipe 70 and then through inlet 78 of pipe 72 above the base of the trough 22 within which water to be drained collects.

Fig. 4 shows a nomogram of the run off rate of rainwater in 1/s against the diameter of drainage pipe in cm against the ratio of the storm rainfall intensity to average annual rainfall intensity. The nomogram can be used in the design of an apparatus according to the present invention for a roof drainage system for a particular climatic location. The curved surface data was derived by calculating the pipe diameter required to drain typical rainfall falling in Central Eastern Scotland from a 18m x 4m test roof by applying hydraulic theory for weir/full bore pipe flow. The roof run off rate required to drain the average annual rainfall intensity for the location in question is estimated. In the example shown 15 1/s is the estimated value. It can be seen from line A that for the average annual rainfall (i.e. when the ratio of the storm rainfall intensity to the annual average rainfall intensity is 1) a single pipe with a diameter of 5cm is required. As storms grow in intensity compared to the average rainfall intensity the need for additional pipes increases.

The ratio of the storm rainfall intensity to the average annual rainfall intensity is estimated, and in this example is estimated to be 3. This shifts line A along and up the curve surface to line B and specifies that to drain the storm rainfall from the roof another pipe of 7cm diameter is required as an outer pipe in an embodiment of the present invention in which the pipes are arranged coaxially, such as that shown in Fig 1.

Fig. 5 shows an example of a nomogram, derived in a similar manner to the nomogram of Fig. 4 and uses the same labelling for the axes, that can be used to design a drainage apparatus according to the present invention for a situation where the storm intensity of the region in question increases to a level where three coaxially arranged pipes are required to drain rainstorm water from a roof. The procedure as described for Fig. 4 is further extrapolated to identify the diameter of the third pipe required to drain storm rainfall when the ratio of the storm rainfall intensity to the annual rainfall intensity is estimated to be 4.5. This shifts line A along and up above the lower curve surface on which line B lies to the upper curve surface and line C from which the corresponding diameter of the third pipe can be determined.

Various modifications may be made to the embodiments described hereinabove without departing from the scope of the present invention.

Claims

C AIMS

1. A siphonic apparatus (1) for draining liquid, the apparatus comprising a plurality of tubular members (4,6), wherein each tubular member (4,6) has an inlet opening (8,10) arranged to be disposed at a different height relative to another opening.

2. A siphonic apparatus (1) as claimed in claim 1, wherein the tubular members (4,6) are disposed in close proximity to one another.

3. A siphonic apparatus (1) as claimed in any preceding claim, wherein the tubular members (4,6) are disposed one within another.

4. A siphonic apparatus (1) as claimed in claim 3, wherein the tubular members (4,6) are arranged coaxially.

5. A siphonic apparatus (1) as claimed in any preceding claim, wherein the tubular members (4,6) are of circular section.

6. A siphonic apparatus (1) as claimed in any preceding claim, wherein the opening (8,10) of each tubular member

(4,6) coincides to the flow area of the respective tubular member (4,6) .

7. A siphonic apparatus (1) as claimed in any preceding claim, wherein the tubular member (6) having the lowermost opening (10) defines a smaller flow area relative to the openings (8) of other tubular members (4).

8. A siphonic apparatus (1) as claimed in claim 7, wherein the flow area of the tubular members (4,6) increases as the height of the inlet openings (8,10) increases .

9. A siphonic apparatus (1) as claimed in any preceding claim, wherein the apparatus includes fixing means (46) for fixing the tubular members (4,6) relative to one another.

10. A siphonic apparatus (1) as claimed in claim 9, wherein the fixing means (46) are adjustable to facilitate varying the relative heights of the inlet openings (8,10).

11. A siphonic apparatus (1) as claimed in any preceding claim, wherein the apparatus (1) includes at least one sliding collar (24) disposed around the inlet (8,10) of at least one tubular member (4,6) to allow the height of the tubular member (4,6) to be raised or lowered.

12. A siphonic apparatus (1) as claimed in any preceding claim, wherein the apparatus includes means (46) for coupling the tubular members (4,6) relative to a surface to be drained (2) .

13. A siphonic apparatus (1) as claimed in any preceding claim, wherein the apparatus includes baffle means (32) for restricting or limiting swirling of liquid flowing into the tubular members, the baffle means (32) being disposed at the opening (8,10) of the tubular member (4,6).

14. A siphonic apparatus (1) as claimed in claim 13, wherein the baffle means include at least one vane (36) .

15. A siphonic apparatus (1) as claimed in claim 13 or claim 14, wherein the baffle means is an anti-vortex plate (32) .

16. A siphonic apparatus (1) as claimed in claim 3 or 4, wherein an anti-vortex plate (32) is included in the opening (8) of the innermost tubular member (4).

17. A siphonic apparatus (1) as claimed in any preceding claim, wherein the apparatus includes a cover means (32) for restricting access of foreign bodies to the inlet openings (8,10) of the tubular members (4,6).

18. A siphonic apparatus (1) as claimed in claim 17, wherein the cover means (32) also serves as a baffle (32) .

19. A building structure having a surface (2) and a siphonic apparatus (1) for draining liquid from the surface (2), the apparatus comprising a plurality of tubular members (4, 6) , wherein each tubular member (4,6) has an inlet opening (8,10) arranged to be disposed at a different height relative to another opening.

20. A method of siphonically draining liquid from a surface (2) , the method comprising: providing a plurality of tubular members (4,6) each having an inlet opening (8,10); locating the inlet openings (8,10) adjacent the surface (2), and arranging each of said openings at a different height relative to the surface (2).

21. A method of siphonically draining liquid from a surface (2), the method comprising: arranging inlet openings (8,10) of a plurality of tubular members (4,6) adjacent the surface (2) , and arranging said openings (8,10) at a different height relative to the surface (2) such that siphonic flow will occur in the tubular members (4,6) in sequence.