The present invention relates to a roof drain comprising a bowl for building into a roof surface, said bowl having a top, a rim at the top, and a bottom; a central outlet opening in the bowl at the bottom thereof for connection with a drain pipe; a vertical axis extending through the central outlet opening; and a substantially flat cover superimposed on the bowl.

A roof drain of the above art is known from US-A-3 469 698, which discloses several embodiments of a roof drain in all of which the cover comprises a central opening around which a circumferential, generally cylindrical wall is provided by elements that may be repositioned to provide inlets between. The inlets may be symmetric to provide a radial flow into the central opening or asymmetric to provide a vortex inducing action. The roof drains disclosed are relatively complicated constructions with many adjustable components. Further the general building height of the roof drain is relatively big with a corresponding large consumption of materials for the construction.

US-A-5 524 393 discloses a roof drain comprising a vortex chamber placed on top of a flat roof. The roof drain including the vortex chamber may be arranged in a sump recessed in the roof surface.

Roof drains of the above art are generally used to regulate the flow of rain water from flat roofs to utilise the roof surface as a storage for rain water in order to avoid that a downstream drainage system is overloaded in case of a heavy rainfall. The provision of a vortex of water in a vortex chamber or bowl of a drain provides a breaking action on the flow to restrict the same while providing for a relatively large cross-sectional area for the flow passage through the drain to avoid blockage by debris in the water. To avoid larger pieces of debris getting into the drain it is known from both of the above documents to provide a grating such as a slotted dome over the drain.

It is an object of the present invention to provide a roof drain as mentioned by way of introduction which avoids at least some of the drawbacks of the prior art.

It is a further object to provide a roof drain that has a simple construction and that may easily be amended to provide a flow characteristic according to the needs at a site of installation.

This is obtained by a roof drain comprising a bowl for building into a roof surface, said bowl having a top, a rim at the top, and a bottom; a central outlet opening in the bowl at the bottom thereof for connection with a drain pipe; a vertical axis extending through the central outlet opening; and a substantially flat cover superimposed on the bowl, wherein an asymmetric inlet is provided in the cover for directing water present on the roof surface into the bowl such as to provoke a swirling motion of the water inside the bowl around the axis, said asymmetric inlet opening being asymmetric relative to a plane defined by the central axis and a radial line in the cover through the central axis and the asymmetric inlet. By providing asymmetric inlets in the substan- tially flat cover a simple construction is obtained together with a low building height since the cover may be flush with the roof surface allowing water on the roof to flow directly onto the cover and down through the inlet whose asymmetry will provoke a swirling motion to induce a more or less pronounced vortex in the bowl.

In an embodiment the bowl has a conical portion extending downwards from the rim, the cover comprises a sheet material, the asymmetric inlet being provided by an incision having a first part extending along the rim and a second part extending from the rim towards a centre of the cover allowing a flap of the sheet material to be bent into or out of the bowl to provide the asymmetric inlet. This provides for a very simple and versatile construction since the inlet results in different flows dependent on whether the flap of the sheet material delimited by the incision is bend into or out of the bowl. Thus when bent into the bowl a free edge of the flap may abut on the internal surface of the bowl to provide the inlet with a channel directing the water in a circumferential direction of the bowl. When bent out of the bowl, or even removed, the flap will leave an asymmetric inlet opening having a wide end and a narrow end in either circumferential direction that will provoke a swirling mo- tion of the water flowing through the inlet opening, but in an opposite direction compared to the situation when the flap is bent into the bowl.

In an embodiment the sheet material is perforated along a line extending between distal ends of the incision. This facilitates the bending or re- moval of the flap of sheet material delimited by the incision.

In an embodiment a number of asymmetric inlets are provided equi- distantly along the rim. Thus a number of inlets may be provided to provide a flow characteristic wanted for the instance.

In an embodiment an orifice member is provided below the cover in- side the bowl to provide a vortex chamber in the bowl between the cover and the orifice member, said orifice member having a central orifice providing an outlet from the vortex chamber. Hereby the flow characteristic may be further adjusted to provide a flow characteristic wanted for the instance since the size of the orifice influences the flow characteristic, which accordingly may be al- tered by providing an orifice member with an orifice of a different size.

In a further embodiment a pipe is extending downwards from the orifice member coaxially with the central orifice. Such pipe may under certain circumstances run full and provide a suction or siphon effect. Thus the flow characteristic may be further adjusted to provide a flow characteristic wanted for the instance.

In an embodiment the cover has an additional opening and an overflow pipe is extending upwards from said additional opening thereby providing an overflow inlet to the bowl at a higher level compared to the asymmetric inlet(s). Hereby the overall flow characteristic is further adjusted to provide a flow characteristic wanted for the instance due to the fact that a significantly larger flow is provided for when the level of water on the roof has reached the higher level. Thus the additional opening and the overflow pipe will provide an emergency overflow to avoid an excess amount of water on the roof.

In a further embodiment in which an orifice member with an orifice is provided inside the bowl and wherein the additional opening and the orifice are coaxial relative to a second vertical axis, the additional opening has a smaller diameter than the orifice. This allow the water flowing through the ad- ditional opening to flow through the orifice together with the water flowing through the asymmetric inlet(s) without the two flows blocking each other.

In an embodiment the first and the second vertical axes are coincident.

In an embodiment a perforated shielding member is provided above the cover. Hereby entry of large debris into the roof drain is avoided.

In an embodiment the cover and, if present, the orifice member are exchangeable. Hereby is obtained that with a bowl of one embodiment and size a number of roof drains having different flow characteristics may be pro- vided.

In the following the invention will be explained in further detail with reference to the accompanying schematic drawings which illustrate by way of example different embodiments. In the drawings,

Fig. 1 shows a side view of a roof drain according to the present in- vention;

Fig. 2 shows a top plan view of the roof drain of Fig. 1 ;

Fig. 3 shows a top plan view of the roof drain of Fig. 1 omitting a grating;

Fig. 4 shows an exploded sectional side view of the roof drain shown in Figs. 1 and 2 sectioned along line IV-IV indicated in Figs. 2 and 3;

Fig. 4a shows part of Fig. 4 in a not in scale view showing more clearly details:

Fig. 5 shows a top plan view of a bowl of the roof drain shown in Fig.

1 ;

Fig. 6 shows an orifice member;

Fig. 7 shows a sectional side view of a part of the roof drain of Fig. 1 with different insides, sectioned along line VII-VII in Fig. 8; and

Fig. 8 shows a top view of the roof drain of Fig. 7 omitting a grating. Referring to Figs. 1 to 6, the drawings show an embodiment of a roof drain according to the invention comprising a bowl 1 and a cover member 3. In the present embodiment the bowl is shaped as an inverted, stepped, truncated cone with an upper rim 5, a first conical portion 7 extending downwards from the rim 5 to a step 9, the function of which will be described below, and a lower, second conical portion 1 1 .

The second conical portion 1 1 is truncated to provide a central outlet opening 13 at a bottom of the bowl, of a size appropriate to fit a drain pipe or a drain hose with which to roof drain is to be connected when installed at a given site. A cylindrical spout 15 for connection with such drain pipe or drain hose is attached to the second conical portion 1 1 around the central outlet opening 13.

The rim 5 is provided with holes 17 for fasteners such as screws. The cover member 3 comprises as central cover portion 19 for covering the conical portions 7, 1 1 of the bowl 1 , and a flashing portion 21 surrounding the central cover portion 19 to seal between the bowl 1 and the roof covering of a roof in which the roof drain is installed. Thus the central cover portion 19 provides a cover superimposed on the bowl 1 , when the cover member 3 and the bowl are assembled. The flashing portion 21 comprises holes 23 for insertion of fasteners, when installing the roof drain in a roof, and holes 25 for fasteners such as screws for fastening the cover member 3 to the bowl 1 .

The cover member is in an embodiment made from a single piece of sheet material and in another embodiment the cover member is made from two different pieces of sheet material whereby the central cover portion 19 is made from one sheet material and the flashing portion 21 is made from another sheet material, which facilitates selecting respective materials suitable for the two portions.

The central cover portion 19 comprises several openings for letting water into the drain. To provide for at least one inlet 27 the central cover portion 19 has in the embodiment shown six incisions 29 each comprising a first part 31 extending along the rim 5 of the bowl, when the bowl and cover member are assembled, and a second part 33 extending towards the centre of cover member. Thus, in the embodiment shown, the second parts of the incisions extend along radial lines extending from a vertical central axis 35 of the roof drain. Perforations 37 extend between distal ends 31 a, 33a of the re- spective first and second parts 31 , 33.

In use when the roof drain is installed in a flat roof and rain falls on the roof, water will flow from the surface of the roof onto the cover of the roof drain, i.e. the central cover portion 19, and into the inlet(s) 27. In the embodi- ment shown in the drawings the cover, i.e. the central cover portion 19 is flat, but it should be understood that a slight curve, either up or down will not disturb the function of the roof drain as long as the water may flow onto the cover from the surrounding roof surface, when a certain small height of water is present on the roof surface.

The respective first and second parts 31 , 33 and the perforations 37 circumscribe flaps 39 of the sheet material. The flaps 39 can selectively be bent around their respective perforation 37 either down into the bowl 1 or up and away from the bowl. In the latter case the flaps 39 may be detached from the sheet material by cutting or breaking the perforations 37.

Bending or removing a flap 39 will provide an asymmetric inlet 27 with an asymmetric inlet opening 27a in the central cover portion 19. The asymmetry of the inlet 27 is in relation to a plane defined by, i.e. comprising, the central axis 35 and a radial line 41 through the inlet proper and the central axis 35. By bending down a flap 39 as shown in Figs. 3 and 4 (which show two diametrically opposite flaps bent down) a side 43 of the flap 39 adjacent the first part 31 of the incision may be brought into engagement with the first conical portion 7 of the bowl 1 thereby providing as a part of the asymmetric inlet 27 a circumferential channel for guiding water from the roof surface down into the bowl 1 in a swirling motion in a clockwise direction as indicated in Fig. 3 by arrow 45. Thus the flap 39 functions as a guide plate.

Due to the swirling motion mentioned above a vortex will be generated inside the bowl below the cover element, and the bowl will form a vortex chamber. This vortex chamber can be delimited downwards by an orifice member 47, which may rest on the step 9. Thus the vortex chamber is delim- ited by the central cover portion 19, the first conical portion 7 and the orifice member 47.

In the embodiment shown the orifice member 47 is a circular piece of sheet material and it has a central coaxial orifice 49 having a diameter. Below the orifice 49 a pipe 51 is extending from the orifice member 47. The pipe 51 has an internal diameter that may be equal to the diameter of the orifice 49, but in the embodiment shown is slightly larger. The orifice 49 provides an outlet of the vortex chamber. Due to swirling motion of water running through the orifice 49 a centrifugal force may pull the water to the inner surface of the pipe 51 even if the internal diameter of the pipe 51 is slightly larger than the diameter of the orifice 49.

At the centre of the central cover portion 19 an additional opening 53 is provided. The additional opening 53 is surrounded by an overflow pipe 55 extending to an overflow level 57 higher than the level of the inlet opening(s) 27a. The additional opening 53 and the overflow pipe 55 are coaxial with the vertical central axis 35. The overflow pipe 55 is shown to be cylindrical. It might however e.g. be wider at its top, i.e. funnel-shaped, to provide for a lar- ger flow.

Apart from the elements mentioned above a perforated shielding member in the form of a grating 59 is provided above the central cover portion 19 to avoid that debris on the roof, such as leaves, twigs, bits of paper, etc. get into the inlet openings 27a and risk blocking the drain. The grating 59 may e.g. be made from a sheeting material provided with slots (not shown in Figs. 1 and 4, but indicated in Fig. 7). The grating may have any appropriate shape: cylindrical (as shown), domed, conical, etc.

The roof drain works as follows.

For a given site, i.e. a given flat roof, of installation it will be a wish to have a roof drain having a certain flow characteristic to provide for retaining water on the roof for some time at an event of rain, especially heavy rain, to avoid overload of a downstream piping system such as a sewer system. For retaining water on the roof a breaking effect is obtained by providing for the formation of a vortex in the bowl 1 possibly in a vortex chamber above the orifice member 47. Also the combined area of the inlet openings 27a is used to control the breaking effect of the roof drain. Thus to obtain the largest breaking effect to retain as much water on the roof for as long time as possi- ble a small number of flaps 39 are bent down into the bowl 1 for abutment on the inside wall of the first conical portion 7 as described above. It is preferred provide inlet openings 27a symmetrically relative to the central axis 35 to provide for a vortex swirling coaxially with the central axis 35. Thus preferably at least two diametrically opposite flaps 39 are bent down.

If larger flows are wanted more flaps are bent down. Thus three, four or six flaps may be bent down still providing for a coaxial swirl of water in the vortex chamber. Bending down more flaps may be accompanied by providing an orifice member 47 having an orifice with a larger diameter.

If even smaller breaking effect is pursued flaps 39 should be bent up or removed instead of bending down flaps. The removed flaps will leave asymmetric inlet openings 27a having in a circumferential direction a wide end at the second part 33 of the incision and an opposite narrow part at the distal end 31 a of the first part of the incision. This asymmetry will provide for a deflection of the flow of water in to the inlet opening 27a thereby providing for a swirling flow in the bowl 1 . However in this case the swirl will be in the opposite direction compared to the situation when the flaps are bend down and the swirl will be less pronounced or vigorous. Thus a smaller breaking effect will be provided, and a larger flow will occur. To provide for a still larger flow the orifice member may be dispensed with.

If during heavy rain the level of water retained on the roof in which the roof drain is installed raises above the overflow level the water will flow into the overflow pipe 55 thereby increasing the flow through the roof drain to limit the amount of water retained on the roof. The water flowing through the overflow pipe 55 will enter centrally into the orifice 49 and the combined flow of water through the overflow pipe 55 and the inlet opening(s) 27a may fill the cross sectional area of the pipe 51 below the orifice member which will thereby provide a suction or siphon effect providing for a larger flow through the orifice member.

Figs. 7 and 8 illustrate further the versatility of a roof drain according to the invention. Thus the insides, including the orifice member and the central cover portion, of the roof drain described above have been removed, and instead a central tube 61 with three supporting fins 63 resting on the step 9 has been inserted. The central tube 61 extends through the cylindrical spout 15 and possibly into a drain pipe 65 connected to the cylindrical spout 15 thereby providing an annular channel 67 that may run full of water being drained from the roof thereby providing a suction or siphon effect enhancing the flow through the drain. The central tube 61 will provide for venting the drain pipe 65 to avoid trapped air blocking the flow of water through the drain pipe. Thus a much larger flow through the bowl 1 described above is provided for.