Vortex brake for a drainage system

This invention relates to a vortex brake for a drainage system having a vortex chamber with a curved wall that surrounds a vortex axis in the vortex chamber; a central outlet in relation to the vortex axis; and a peripheral inlet with an inlet opening, which is defined between two opposite wall portions and between two opposite, free edges extending between the two opposite wall portions and establishing an opening plane, wherein one of the two said wall portions extends cross- wise to the opening plane, and a first inlet wall portion extends from the inlet opening in continuation of this wall portion that extends crosswise to the inlet opening, and wherein a second inlet wall portion in continuation of the first inlet wall portion extends in front of the inlet opening at a distance therefrom. Hydraulic brakes are used in drainage systems to protect the system parts downstream from the brake against hydraulic overload caused by too big a flow. Ideally, a characteristic for the brake is desired in which outlet flow from the brake equals influx up to a certain limit after which increased influx to and resulting impounding at the brake does not give rise to increased outlet flow from the brake.

A vortex brake is a commonly used hydraulic brake for drainage systems and has the advantage of not having movable parts, thus requiring only little maintenance. However, there is a risk of clogging due to solid elements in the drainage liquid. The brake effect in a vortex brake primarily arises in two places. First of all, an eddy in the vortex chamber will create a back pressure in the inlet as a result of centrifugal force. Second of all, there will be a pressure loss in the inlet itself. In addition, the way in which liquid is led through the inlet into the vortex chamber influences the formation of the eddy and its intensity.

In view of the above mentioned risk of clogging, an as big as possible sectional area of flow is desired through the vortex brake for preventing, as far as possible, solid elements in the liquid that flows in

the drainage system from getting stuck in narrow passages in the brake.

A vortex brake of the initial prior art is known from SE-B- 457121, which describes vortex brakes designed with a disc-shaped vortex chamber and a member placed across the inlet at a distance from the inlet opening so as to obstruct direct inflow and thus increase resistance at the inlet. In an embodiment, the vortex brake is designed with a plane front wall and a plane back wall, in which the outlet is located. A cylindrical peripheral wall extends unbroken along the entire periphery of the vortex brake, which is substantially circular, but one place is drawn out to an apex forming an angle of about 90°. At this apex, an opening is provided in the front wall and the back wall. Between the front wall and the back wall, a curved wall is located for guiding the whirling liquid inside the vortex chamber. The said inlet opening is thus provided between a free, downstream end of the curved wall, the peripheral wall, and edges of the openings in the front wall and the back wall; said openings providing access for liquid to the inlet opening.

Other examples of known vortex brakes can be found in US-A-4 834 142, GB-A-2 254 938, and WO-A-92/04667. The purpose of the present invention is to provide a vortex brake having an inlet with relatively great resistance. Thereby bringing the characteristic of a vortex brake closer to the ideal characteristic mentioned above.

This is accomplished by the second inlet wall portion having an end with a free edge remote from the first inlet wall portion. This allows liquid to flow over said free edge, giving the flow of liquid a direction towards the wall portion extending crosswise to the inlet opening, at which wall portion the flow will deflect, causing a further contraction of the flow in relation to what is known. Contraction of the flow generally means that the sectional area of flow is reduced and the speed is increased, and that the static pressure is reduced. The static pressure in the vortex chamber therefore becomes smaller. Consequently, a higher external pressure is required to generate an eddy in the vortex chamber.

In a preferred embodiment, the second of the two opposite wall portions is made up of a shiftable cover plate for adjustment of the size of the inlet opening. In a known way, this allows for adjustment of the characteristic of a given vortex brake. In a preferred embodiment, the cover plate is curved in such a way that it is concave seen from the outside in relation to the vortex chamber. In this way, a further contraction of flow in the inlet is achieved with the effect known from a Borda tube, i.e. an inwards- turned, sharp-edged pipe. Preferably, said end of the second inlet wall portion remote from the first inlet wall portion is connected to said opposite, free edges at the second of the opposite wall portions by means of connecting pieces. These connecting pieces do not obstruct the flow but support the second inlet wall portion. At the same time, the connecting pieces divide the total access route past the second inlet wall portion into three parts. If a larger solid element than allowed by the vortex brake to pass should occur in the liquid flowing in the drainage system, then there is a good chance that it will only block one of said three parts so that flow is still possible. In one embodiment, the wall portion extending crosswise to the inlet opening runs smoothly into the curved wall.

In a second embodiment, the wall portion extending crosswise to the inlet opening extends through a concave curve, as seen from inside the inlet, to an end meeting an edge of the curved wall of the vor- tex chamber. The inlet thus comprises an inlet chamber with cascade effect, which further increases the resistance seen in relation to the sectional area of flow. Preferably, the second of the two opposite wall portions runs substantially smoothly into the curved wall.

Preferably, a cover member with an opening is attached at the outlet in such a way that the lower part of the opening of the cover member is level with the lower part of the opening of the outlet in the mounted position of the vortex brake. This further provides an opportunity to adjust the capacity of a given brake without substantially changing the characteristics, taken to mean the shape of a curve of flow ver-

sus water pressure in front of the brake, and without affecting the flow in cases where this is small.

In a preferred embodiment, the curved wall is cylindrical and extends between a front wall and a back wall, wherein the outlet is pro- vided in the back wall, and both the front wall and the back wall are provided with a coupling means for connection to an outlet pipe so that passage through the vortex brake and the outlet to the outlet pipe is provided when the coupling means of the back wall is connected to the outlet pipe and access to the outlet pipe is blocked when the coupling means of the front wall is connected to the outlet pipe. This provides easy access for blocking flow, if desired.

In a further preferred embodiment, the curved wall is cylindrical and consists of sections with constant radius of curvature. This provides a vortex brake whose vortex chamber is easy to build. In the following, the invention will be explained in more detail by means of exemplified embodiments with reference to the schematical drawings in which

Fig. 1 shows a front view of a first embodiment of a vortex brake without a front wall; Fig. 2 shows a side view of the vortex brake in Fig. 1;

Fig. 3 shows a view corresponding to Fig. 1 of a second embodiment of a vortex brake; and

Fig. 4 shows a side view of the second embodiment.

Figs. 1 and 2 show a vortex brake with a front wall 1, a back wall 2, and an intermediate curved, cylindrical wall 3, collectively surrounding a vortex chamber 4. The vortex brake has a peripheral inlet 5 and a central outlet that is provided at an outlet opening 6 in back wall 2.

In a way known per se, the vortex brake is mounted on a side wall 7 of a well 8 at an outlet 9 from the well. Thus a first coupling part 10, known per se, is mounted on side wall 7. This coupling part 10 has an outlet pipe in the form of a pipe stub 11 which carries a sloping flange 12 with sides that on a level with the pipe stub are parallel and above the pipe stub converge and meet in a point 13. On its back wall

2, the vortex brake carries a second coupling part 14 constructed of bend sheet with holding jaws 15 that are adapted for engaging the parallel sides of flange 12. The central part of the second coupling part 14 abuts back wall 2 and is provided with a through hole 16 of slightly smaller diameter than outlet opening 6. Due to the engagement between the sloping flange 12 and the holding jaws 15, the central part of the second coupling part 14 is pressed sealingly against the end of pipe stub 11 when the vortex brake is mounted, and it is possible to detach the vortex brake by simply lifting it up vertically. To ensure the seal be- tween the end of pipe stub 11 and the central part of the second coupling part 14, sealing material can be provided on the central part of the second coupling part 14 around hole 16.

The peripheral inlet 5 of the vortex brake comprises an inlet opening 17, which is defined between a first wall portion 18 of the cylin- drical wall 3 and a second wall portion 19 of the cylindrical wall 3, said second wall portion 19 being provided by a cover plate 20. The cover plate may be a plane cover plate 20, as shown in solid line, or it may be a curved cover plate 20', as shown in broken line. Inlet opening 17 is further defined by two opposite, free edges 21 of the front wall and the back wall, respectively.

The first wall portion 18 extends crosswise to the plane of inlet opening 17, and a first inlet wall portion 22 extends in continuation of the first wall portion 18, said inlet wall portion 22 having the same width as the first wall portion 18. In continuation of the first inlet wall portion 22, and angled thereto in the exemplary embodiment, is a second inlet wall portion 23 that extends in front of inlet opening 17 at a distance therefrom. This prevents water from flowing from well 8 straight through inlet opening 17 and prevents water from flowing around an edge of the first wall portion 18 and into inlet opening 17. Water may, however, flow past a free edge 24 at the end of the second wall portion 19 and around the free edges 21 into inlet opening 17. This forces an inflowing jet of water down towards the first wall portion 18, and the jet will be contracted sideways between the front and back wall due to the water flowing in around the free edges 21.

Due to the design of inlet wall portions 22, 23 at the inlet to the vortex chamber, a great flow resistance is achieved at the inlet to the vortex chamber.

The effect of an inflowing jet of water being forced down to- wards the first wall portion 18 is heightened by using a curved cover plate 20' because water that flows along the cover plate towards inlet opening 17, flows partially away from inlet opening 17 immediately prior to reaching it as a result of the curve and therefore has to turn more sharply in order to get into the inlet opening than would otherwise be the case.

Two connecting pieces 25 extend between the front wall and the back wall, 1, 2, respectively, and the end of the second inlet wall portion 23 at the free edge 24. They have a small cross section and therefore do not noticeably affect the flow of liquid into the vortex brake. However, they serve the purposes of stabilizing the end of the second inlet wall portion 24, acting as guide for the end of the cover plate 20, 20', as well as acting as a coarse screen that prevents solid items in the flowing liquid from reaching inlet opening 17 and blocking it. For production reasons, the vortex brake is constructed with a plane front wall 1 and a plane back wall 2. The curved wall 3 is designed with sectional constant radius of curvature: From the first wall portion 18, the curved wall 3 extends straight (infinitely large radius of curvature) to a point 26 vertically below the outlet. From there wall 3 extends through 180° with a radius of curvature rl to a point 27 vertically above the outlet where the radius of curvature is reduced to a second radius of curvature r2 as the centre of the radius of curvature is shifted vertically over a distance d. The wall 3 extends through 90° with the radius of curvature r2 after which the curved wall 3 has a small straight section for connection to cover plate 20, 20' that continues the curved wall 3. Between the front and back wall opposite the small straight section 28 is mounted a bar 29 in which there are screws 30 for fastening cover plate 20, 20' by squeezing so that cover plate 20, 20' can be shifted in order to adjust the size of inlet opening 17.

In a way known per se, the vortex brake is provided with a vent pipe 31 at the top for venting vortex chamber 4. The vent pipe 31 may in a similarly known way be provided with a handle (not shown) by means of which the vortex brake can be lifted for detachment or at- tachment, for instance for cleaning.

On front wall 1, the vortex brake is provided with a blind coupling part 32 that is identical to the second coupling part 14 on back wall 2 except from the fact that it lacks a hole corresponding to hole 16. The passage to outlet 9 from the well can therefore be blocked by de- taching the vortex brake, turning it, and mounting it by means of the blind coupling part 32.

At its outlet, the vortex brake is provided with a cover member 33 having a smaller hole than hole 16 in the second coupling part. The circumference of cover member 33 corresponds to the circumference of outlet opening 6 including a bevel 34 which ensures that cover member 33 cannot be turned in outlet hole 6 but can only be placed in one position. As hole 16 has a smaller diameter than outlet opening 6, a peripheral area of the second coupling part 14 around hole 16 is exposed in outlet opening 6 and may be used for securing cover member 33, e.g. by gluing. The cover member 33 has a cover hole 35 which is eccentric to hole 16 in such a way that their edges are coincident in the lowest place 36. Hereby it is achieved that the addition of cover member 33 does not change the outlet conditions during small flow by increasing the outlet threshold, which would otherwise cause constant impounding of a certain amount of water upstream from the vortex brake.

The centre C of hole 16 is coincident with the centre for the radius of curvature r2. As a result of the spiral movement of the water from the inlet to the outlet when an eddy is generated in vortex chamber 4, vortex chamber 4 with the described design will, to a good ap- proximation, correspond to the geometry in the eddy including the fact that the hole for outlet is concentric with the vortex axis.

When the characteristic of the vortex brake is adjusted by shifting cover plate 20, 20' in the direction towards the first wall portion 18, the inflowing jet of water becomes flatter, i.e. smaller in the radial direction of vortex chamber 4, and therefore the geometry of the eddy

rection of vortex chamber 4, and therefore the geometry of the eddy is changed moving the vortex axis downwards. This is countered by cover member 33, whose cover hole 35 in the mounted position is located with the centre lower than centre C of hole 16. Figs. 3 and 4 show a second embodiment which differs from the first embodiment in the design around the inlet. Details such as coupling parts and vent pipes are not shown but could be as shown in figs. 1 and 2.

The actual vortex chamber 4' in Figs. 3 and 4 has a plan front wall 1' and back wall 2', and a curved, cylindrical wall 3' has a straight section 37 which runs smoothly into a section extending through 180° with a radius rl', onwards through 90° with a smaller radius r2', and further onwards through about 40° with an even smaller radius r3 to an inner edge 38. At inlet 5', the vortex brake in Figs. 3 and 4 is provided with an inlet chamber 39 having a curved wall 40 with a radius of curvature r4 that extends from inlet opening 17' of the vortex brake to the inner edge 38 of the curved wall 3' of the vortex chamber. At inlet opening 17', a wall portion 18' of the curved wall 40 extends- crosswise to the plane of inlet opening 17', whereas an opposite wall portion 19' is made up of an end of the straight section 37 of the vortex chamber's curved wall 3'. Two free edges 21' of the front and back wall 1', 2' of the vortex brake extend between these two wall portions 18', 19'. In continuation of the curved wall 40, a first inlet wall portion 18' extends beyond inlet opening 17', and a second inlet wall portion 19' extends from the first inlet wall portion 18' in front of inlet opening 17' at a distance therefrom in essentially the same way as in the embodiment in Figs. 1 and 2. Connecting pieces 25' extend from the free end of the second inlet wall portion 19' to the front and back wall 1', 2', respectively, as in the em- bodiment in Figs. 1 and 2.

A cover plate 20" is mounted movably at the second wall portion 19' by means of screws 30' to allow for adjustment of the size of inlet opening 17'.

At the outlet, a cover member 33' with eccentric cover hole 35' is mounted in the same way as described with reference to Figs. 1 and 2.

The design of inlet 5' with an inlet chamber, wherein an inflow- ing jet of water is forced round along the curved wall 40 so that a thin, contracted jet is led tangentially into vortex chamber 4', gives even greater inlet resistance than inlet 5 in Figs. 1 and 2. The vortex brake shown in Figs. 3 and 4 is thus suitable for use in places where great impounded heights may occur. To prevent dirt from depositing on the outside of the curved wall 40 of inlet chamber 39, a shading wall 41 is provided, said shading wall providing a cavity 42 between the front and back wall 1', 2'.

Due to the design of the inlet, cover member 33' shown in Fig. 3 cannot be introduced through it (in the embodiment shown in Figs. 1 and 2 this is possible by removing cover plate 20, 20'). Cover member 33' is therefore cut at A making it possible to screw cover member 33' through hole 16' of the outlet. Alternatively, cover member 33' can be divided into two along a diameter B making it possible to introduce the two halves separately through hole 16' and glue them on.