GB2347451A

GB2347451A - Anti-vortex fins for drainage assembly

Info

Publication number: GB2347451A
Application number: GB9904443A
Authority: GB
Inventors: Zbigniew Zygmunt Wereszczynski
Original assignee: MARLEY ALUTEC Ltd
Current assignee: MARLEY ALUTEC Ltd
Priority date: 1999-03-01
Filing date: 1999-03-01
Publication date: 2000-09-06
Anticipated expiration: 2019-03-01
Also published as: GB2347451B; GB9904443D0

Abstract

A drainage assembly comprises a drainage bowl 4 with a drainage hole 5 situated therein, a dome grate 1, centred on the drainage hole 5 and attached to the bowl 4 via an intermediate annular member 3. A plurality of elongate baffle elements 2 which reduce or prevent vortex formation are located transversely of the grate wherein the elements protrude through holes in the grate and thereby inhibit or reduce vortex formation outside of the grate.

Description

DRAINAGE ASSEMBLY AND ANTI-VORTEX FINS THEREFOR This invention relates to a drainage assembly and to anti-vortex fins which are used in such drainage outlets and fittings for incorporation into buildings with flat roofs, patios, roads or other paved surfaces and the like in order to drain the area into a pipework system.

Waste screens for drainage outlets are well known and have been designed in a variety of shapes and sizes, and with a number of configurations.

There are two main types of drainage system used for draining water; they are known as gravity and syphonic systems. Gravity systems work essentially at atmospheric pressure and rely on providing a drain at a low point on the roof or other surface. These systems are reliable and easy to install although they require the use of relatively large diameter pipe work in order to maximise their efficiency. Indeed, due to air entrainment in the ingressing water such systems, even when operating at their maximum efficiency, are only about one third full of water.

Syphonic systems, on the other hand, can operate at about 90% capacity and as a reflection of this can be installed with relatively smaller diameter pipe work. However, due to the nature of syphonic systems they require a great deal of care and attention whilst installing and in operation. The large pressure differences and vibrations, which are generated through use, coupled with the requirements for special venting arrangements and high maintenance costs mean that syphonic systems are not practicable for a variety of users and in a variety of situations.

In order to increase the efficiency of gravity systems the amount of water transferred through the system per unit time must be increased. Once the pipe diameters have been matched to the requirements of the drainage catchment area, taking into account such parameters as typical rainfall volume for example, the only parameter which can be modified is the amount of air entrainment in the system.

Typically when water drains down a hole a vortex is produced. The rotating water column has, at its centre, a cavity that propagates down the opening of the drainage system. This obviously reduces the efficiency of the system as it affects the bulk volume of water transferred per unit time. Another issue affecting the efficiency of the system is the prevention of blockages at the entrance to the outlet. The simplest outlets consist of perforated plates placed over the outlet. However, such perforations are quickly occluded by vegetable or plant matter, and/or refuse and the like and therefore have been superceded by more complex grates.

Several proported solutions to the problem of reducing the air entrainment in the water stream have been reported. Harmer Holdings (WO 94/18414) have reported a system whereby a vane is placed into a drainage fitting in order to reduce vortex formation. The vane is mounted on a clamping ring which is situated underneath the grate and is secured to the body component. The vane and clamping ring are secured together, and in the outlet by a number of screws which makes maintenance and retrofitting difficult.

Aeromator (WO 84/04126) discloses a waste screen that prevents vortex formation by providing a plate situated parallel to, and vertically spaced from, the opening. The distance of the plate above the opening is carefully calculated so that the gap between plate and opening is entirely filled with water, turbulence is reduced and the efficiency of the system is increased. This requires a careful consideration of the parameters involved, such as volume throughput of water and so on.

A different approach has been adopted by Schmid (US 2689017). He teaches that a vane may be placed in a drain outlet in order to reduce the amount of vortex formation in the outlet. This again uses a number of nuts and bolts to secure clamping rings and the like and hence suffers from similar restrictions to Harmer.

The present invention aims to mitigate the problems of vortex formation in gravity drainage systems and thereby increase the efficiency of such systems.

The present invention also proposes solutions to the problems associated with prior art drainage systems and provides means to retrofit anti-vortex fins to existing drainage outlets.

Accordingly, the first aspect of the present invention provides a drainage bowl with a drainage hole situated therein, a dome grate, centred on the drainage hole and attached to the bowl via an intermediate annular member, and a plurality of elongate baffle elements which reduce or prevent vortex formation and are transversely located of the grate wherein the elements protrude through holes in the grate.

In a further embodiment the baffle elements are connected so as to form a one piece, rotationally symmetrical, baffle. Preferably the baffle comprises an edge, closest to the outlet, which is supported by the grate.

In a further embodiment the axes of adjacent baffle elements are separated by either 90 or by 120 .

Preferably the grate comprises two sets of circumferentially situated drainage holes, each set situated at a particular vertical displacement from the outlet.

Preferably the baffle elements protrude through holes of the set of holes with the larger vertical displacement from the bowl.

In a further embodiment the baffle edge defines a weir level of water in the bowl Preferably each element has a distal edge which is shaped so as to cooperatively mate with a part of the assembly.

In another aspect of the current invention there is provided a baffle for reducing vortex formation in a drainage outlet comprising a plurality of elongate baffle elements which, in use, extend transversely of a dome grate and protrude through holes therein.

In one embodiment the baffle comprises a central pillar to which each element is attached, and in another it comprises a main elongate element to which two subsidiary elements are attached.

Preferably the baffle has a rotational symmetry greater than 1, and the distal edges of the baffle elements are shaped so as to cooperatively mate, in use, with a shaped drainage bowl.

A preferred embodiment of the invention will now be described with reference to the accompanying drawings in which: Figure 1 A side elevation of a drainage outlet provided with fins according to the present invention.

Figure 2 A plan view of the drainage outlet provided with fins according to the present invention.

Referring to the drawings, a dome grate assembly for a gravity drainage system comprises a dome grate 1 and anti-vortex fins 2 in a cruciform or cross-shape configuration. The grate 1 is secured to a clamping ring 3 by screws 10, or like fasteners, through tabs 11 situated at the base of the grate, thereby bringing the base of the grate 1 into mating relations with the clamping ring 3.

The ring 3 clamps a waterproof member (not shown) to a drainage bowl 4 into which water runs before draining through outlet 5. The drainage bowl 4 is secured to the roof or like structure and provides a lip 9 upon which the ring 3 is located. The ring 3 is further secured by securing studs (not shown). The grate 1 comprises of a plastics or metal hollow, perforated, structure with principal drainage holes 6 and subsidiary drainage holes or slots 7.

Situated within the grate and protruding therefrom are the fins 2. These fins are formed from aluminium, or from any durable material such as plastics (e. g.

Teflon (RTM), polyethylene, nylon) or galvanise steel. The cross-shaped fins are constructed from three pieces, a cross-piece 22 and two arms 23. The arms 23 are of substantially L-shaped form and these are bolted or riveted to the crosspiece 22 to form a cross. For example aluminium captive bank nuts may be used to hold the pieces together.

The cross-shaped fins 2 may also be constructed from four identical individual members which are supported on a central post. Each member being provided with a form, on it's proximal end, which locks into a complementary form on the central member. Thus a slot in the proximal end of each of the members will interlock with a spigot, or other male member, situated on the central post.

In such a way a symmetrical array of fins about a central post can be constructed.

The fins 2 are constructed in situ and protrude through the secondary holes 7 of the grate 1. The fins 2 are supported on the grate 1 and are prevented from rotating by the struts which define the secondary holes 7. The four arms of the fins are provided, at their leading edge, with a shaped component 12. This allows for complementary mating between the fins 2 and the clamping ring 3.

This particular configuration of principal 6 and subsidiary holes 7 gives the dome grate assembly 1 dual functionality. When the volume of water draining into the bowl 4 from the catchment area is low the water simply drains via the principal holes 6 into the outlet 5. In this instance when the volume of water passing through the outlet 5 is low the system can cope with the entire body of water and vortex formation is not considered to be a problem.

As the volume of water increases the principal holes 6 become less and less able to cope with the demand and water builds up in the bowl 4. When the water level reaches a"weir level"8 the secondary holes 7 have to be used. As the throughput of water increases, the bulk momentum of ingressing water increases, and the problem of vortex formation becomes apparent.

Water draining from a roof, or like structure, runs along the roof and enters the drainage bowl 4 of the assembly. As the water runs into the drainage bowl 4 its velocity increases and an angular, or circumferential, component to its velocity is developed. This increase in the angular velocity is the start of vortex formation. The fins 2 inhibit the build up of the angular component of the water's velocity. The ingressing water can only develop a small angular velocity component before it comes into abutment with a fin 2. The fin 2 thereby removes the angular momentum from the water.

Therefore any angular component of the water's velocity has been reduced, or completely removed, before the water passes through the grate 1. The fins 2 effectively channel the water into the outlet 5 with a linear rather than circumferential flow.

The position of the fins 2, as supported on the grate 1, is such so that they only alter the passage, and direction, of the water once the water level has risen above the weir level 8. In low volume throughput conditions the fins 2 allow for a free flow of water into the outlet 5.

The principal holes 6 are likely to become occluded with plant matter or rubbish. When this happens the bowl 4 will fill even in low throughput conditions. In such a scenario the secondary holes 7 will still allow adequate drainage and will continue to do so under all conditions for a considerable time. As the bowl fills, under high throughout conditions, the efficacy of the fins will not be affected; they will still prevent vortex formation within the body of water.

The number of fins 2, which protrude from the grate 1, can be altered. For example a symmetrically arranged three fin system could be used or indeed any arrangement with greater than two radial protrusions.

Claims

CLAIMS 1. A drainage assembly comprising a drainage bowl with a drainage hole situated therein, a dome grate, centred on the drainage hole and attached to the bowl via an intermediate annular member, and a plurality of elongate baffle elements which reduce or prevent vortex formation and are located transversely of the grate wherein the elements protrude through holes in the grate and thereby inhibit or reduce vortex formation outside of the grate.
2. An assembly according to claim 1, wherein the baffle elements are connected so as to form a one-piece rotationally symmetrical baffle.
3. An assembly according to claim 2, wherein the baffle comprises an edge which is supported by the grate.
4. An assembly according to claim 3, wherein the axes of adjacent baffle elements are separated by 90 .
5. An assembly according to claim 3, wherein the axes of adjacent baffle elements are separated by 120 .
6. An assembly according to any preceding claim, wherein the grate comprises two sets of circumferentially situated drainage holes, each set situated at a particular vertical displacement from the outlet.
7. An assembly according to claim 6, wherein the baffle elements protrude through holes of the set of holes with the larger vertical displacement from the outlet.
8. An assembly according to claim 7, wherein the edge defines a weir level of water in the bowl
9. An assembly according to claim 5 to 8, wherein each element has a distal edge which is shaped so as to cooperatively mate with a part of the assembly.
10. A baffle for reducing vortex formation in a drainage outlet comprising a plurality of elongate baffle elements which, in use, extend transversely of a dome grate and protrude through holes therein and thereby inhibit or reduce vortex formation outside of the grate.
11. A baffle according to claim 10, comprising a central pillar to which each element is attached.
12. A baffle according to claim 10, comprising a main elongate element to which two subsidiary elements are attached.
13. A baffle according to claim 11 or 12, wherein the baffle has a rotational symmetry greater than 1.
14. A baffle according to claim 10 to 13, wherein the distal edges of the baffle elements are shaped so as to cooperatively mate, in use, with a shaped drainage bowl.
15. An assembly as described herein and with reference to the accompanying drawings.
16. A baffle as described herein and with reference to the accompanying drawings.