GB2277460A

GB2277460A - Screen grid for overflow tanks

Info

Publication number: GB2277460A
Application number: GB9408350A
Authority: GB
Inventors: Werner Nill
Original assignee: Individual
Current assignee: Individual
Priority date: 1993-04-30
Filing date: 1994-04-27
Publication date: 1994-11-02
Anticipated expiration: 2014-04-27
Also published as: GB9408350D0; AT400599B; GB2277460B; FR2704449A1; ATA81894A; DE9406644U1; DE4413841A1

Description

2277460 SCREEN GRID ARRANGEMENT FOR OVERPLOW TANKS The subject matter of

the present invention is a screen grid arrangement for overflow tanks, flood relief installations and the like, having grids comprising rods or ropes disposed parallel to one another and next to one another and attached by their ends to a framework, said grids being mounted on an overflow wall, and whose through-passage surface, acting as a grid, is disposed at an angle of from 450 to 900 to the horizontal, and having a retaining wall f or raising the retained level to the level of the upper edge of the grid.

In the case of heavy rainf all, the waste water arriving at a sewage plant can no longer be directly fed as a whole to the treatment process, because the capacity of sewage plants is not designed to accommodate the maximum possible inflow. For this reason, sewage treatment plants are preceded by rain overflow tanks into which the incoming water is first diverted on such occasions. As long as the incoming amount of water can be absorbed by the treatment plant, no water flows to a main outfall or directly to a standing body of water. If the incoming amount of water exceeds the capacity of the treatment plant, the proportion which exceeds this capacity is diverted into the rain overflow tank. In order, however, to enable the coarsest impurities, particularly the floating ones, to be held back, the water is passed through screens or grids. In this respect it is possible to move water through such screens or grids f rom the bottom upwards, in order to wash back the retained impurities after the rainfall and the like pass them to the treatment plant. A vertically- disposed grid can also fulfil this purpose, instead of a horizontal grid or screen. Such grids are conventionally disposed on an overflow rim separating the rain overflow tank from the feed to the main outfall.

The flow through a grid mounted on the overflow rim is predominantly concentrated on the portion adjacent to the overflow rim, as in many cases the water level on the inflow side does not reach as far as the upper edge of the grid. Therefore there rapidly occurs a build-up or clogging of this area and therefore an undesired increase in the height of the overflow rim, with a consequent change in the hydraulic circumstances.

It is already know to dispose on the outflow side of the overf low rim a flood plate or a retaining wall whose upper edge corresponds with the desired hydraulic overflow rim height. In this way water passage through the grid begins only when at least the greater proportion thereof lies beneath the water level of the inflow side. Such a grid arrangement solves the problem of partial contamination of the grid when there is a small amount of overf lowing water. If, on the other hand, the water level rises above the upper edge of the grid, impurities can pass over the latter into the intermediate space between the grid and the overflow rim extension, and when the water flow goes down are deposited, along with finer impurities floated through the grid, behind said grid in the Vshaped slot between the grid and the overflow rim extension. cleaning of such a grid, and of its vicinity on the wall, which is usually made of concrete, is expensive.

The purpose of the present invention is to provide a screen grid arrangement for overflow tanks in which contamination of the grid is kept low when there is a small amount of overflowing water, and in which, after the rainfall, the retained impurities can be removed in a simple way.

2 1 P_ According to the present invention there is provided a grid arrangement for rain overflow tanks, flood relief installations and the like having grids comprising rods or ropes disposed parallel to one another and next to one another and attached by their ends to a framework, said grids being mounted on an overflow wall, and whose through-passage surface, acting as a grid, is disposed at an angle of from 450 to 900 to the horizontal, and having a retaining wall for raising the retained level to the level of the upper edge of the grid, in which the bottom portions defining at the foot the space formed by the grid and the retaining wall are disposed to be inclined at an acute angle to the grid bars or ropes, and are connected at their lowest point with a backpressure flap leading into the relief channel By means of oblique positioning, in sections, of the crown of the overf low wall upon which the grid and the retaining wall are mounted, the impurities retained between the grid and the overflow plate can be collected and passed to the treatment plant after the rainfall. Return of the impurities is effected automatically after a drop in the water level. A wall which is disposed on the inlet side of the grid, dips into the surface of the inlet-side water level, and is vertically adjustable in dependence on the water level, prevents floating impurities from being floated against the grid during the rise in the level of the inflowing water. By means of a float, the submerged wall is raised as soon as the water level has reached a predeterminable appropriate height.

bridge overspanning the overflow wall prevents impurities from passing between the grid and the overflow wall, as during a heavy rainfall its water mass can no longer be diverted through the grid alone.

In a special embodiment both the height and the length of the overflow bridge are movable and adjustable. Either a comb driven by a motor through a cylinder, or a sprinkler installation, can be used to clean the grid.

The present invention will be further illustrated by way of example, with reference to the accompanying drawings, in which:

Fig. 1 is a cross-section through a rainwater tank along line I-I in Fig. 2; Fig. 2 is a cross-section through the overflow wall along line II-II in Fig. 1; Fig. 3 is a cross-section through a further embodiment of a screen grid arrangement on an overflow wall, and Fig. 4 is a cross-section through a rain overflow tank with an adjacently- located flood relief channel.

In the tlood water relief installation 1 shown diagrammatically and in cross-section in Fig. 4, there can be seen on the left-hand side a rain overflow tank 3, and on the right-hand side a relief channel 5. The relief channel 5, which lies on a higher level than the overflow tank 3, is separated from the overflow tank 3 by an overflow wall 7 with an overflow rim 9. Mounted on the overflow rim 9 is a vertically-upright grid 11 with grid bars, e.g. f lat iron components 12. The bars are connected by their ends to the vertical portions of a framework 15.

A travelling comb 21 can be disposed on the inlet or on the outlet side, its teeth being attached to a vertical beam 24, and engaging in the interspaces between the adjacently-lying bars 13. The comb 21 can be suspended on a support roller and guided in a rail on the framework 15 of the grid 11, and can be driven in a 1 horizontally travelling manner by a motor drive with a chain, or by a hydraulic, pneumatic or electrical linear drive.

In the first embodiment according to Figs. 1 and 2, the grid 11 is set obliquely with respect to the vertical, in order to obtain an increase in the grid cross-section with a constant grid height. The lower edge of the grid 11 is at an acute angle to the horizontal on the upper edge 23 of the overflow wall 7. Continuing from the upper edge of the framework 15 of the grid 11 is an overflow bridge 25 which has a verticallyextending portion 27 reaching as far as the level h2, and a horizontal portion 29 which extends horizontally over the upper edge of a retaining wall 31 f orming the dam height hi. The vertical portion 27 and the horizontal portion 29 can be displaceable and adjustable in their length or height respectively. A tubular nozzle 33 is mounted on the horizontal portion 29 of the overflow bridge 25 through which nozzle drive for the comb 21 may be effected, without overflowing water being able to pass from above into the V-shaped interspace 37 between the retaining wall 31 and the outlet- side surface of the grid 11. Both the overflow bridge 25 and the retaining wall 31 may be made of sheet metal. In order to support the pressure forces of the rising water acting on the inlet side, the grid 11 may be connected by bracings 35 with the cover or the walls of the structure 1. The substantially V-shaped space 37 between the retaining wall 31 and the grid 11 has bottom portions 39 (cf. Fig. 1) which extend at the foot at an acute angle to the grid bars 13, i.e. are inclined to the horizontal, and at the lowest point of which there is disposed a backpressure flap, each opening into the relief channel 5, and with a pipe 41 with a pivotal lid 43. The bottom portions 39 can be integrally formed in the overflow wall 7 during its manufacture, or be in the form of a tank 45 made of sheet metal. The bottom portions 39 are also more advantageously disposed so as to be inclined in the direction of the relief channel 5. In addition, this tank 45 can be directly connected to the retaining wall 31, or the latter can form part of the tank 45, the entire structure being mounted on the overflow wall 7.

Depending on the length of the grid 11 onef two or a plurality of such Vshaped tanks 45 are disposed next to one another on the overflow wall 7. The tanks 45 can be works-prefabricated and included after the structure has been erected, e.g. mounted on the crown of the overflow wall 7.

A retaining wall 49 is disposed on the inlet side of the grid 11 and on its framework 15, said wall 49 being mounted to pivot about a horizontal linkage 47. Additionally attached to the retaining wall 49 is a float 51, by means of which the position of the retaining wall 49 is adapted to the level of the water on the inlet side in the relief channel 5. A buffer 53 prevents the retaining wall 49 from being raised in a counterclockwise direction above the vertical position shown in Fig. 2, when the water level rises sharply. The lower edge of the retaining wall 49 can have a curved-over portion in order to prevent access of impurities to the grid when the water rises. In addition to the pivotal retaining wall 49, there may also be disposed on the cover or the walls a stationary submerging wall 50, which serves to hold back the inflowing impurities during emergency relief outlet via the overflow bridge 25.

In the development of the invention according to Fig. 3, the grid 11 id disposed vertically. The design and position of the overflow bridge 25 corresponds to i 11 - 7 that in the first embodiment.

Instead of a pivotal retaining wall, in the second embodiment a retaining wall 55 is vertically displaceably mounted in two vertically-attached guide rails 57. A float 51 is attached to the retaining wall 55, similarly to the first embodiment by means of which f loat 51 the position of the retaining wall 55 may be adapted to the height of the water level in the relief channel 5 at any time. In the topmost position of the retaining wall 55, the latter serves as a submerging wall for emergency relief, when the water flows off over the overflow bridge 25 at level h2. The retaining wall 55 can hold back not only floating impurities 61, but also oil. There is preferably disposed on the overflow wall 7, level with the lower end of the guide rails 57, a closure strip 59, which prevents floating impurities from passing through behind the retaining wall 55.

The method of operation of the grid arrangements will now be described in more detail.

At the beginning of the rainfall, when the water level in the relief channel 5 has not yet reached the float 51, the retaining wall 49 abuts, in the position shown in continuous lines in Fig. 2, against the overflow wall 7 and at first prevents entry of floating impurities 61 on the rising water into the space f ormed by the overflow wall 7, the grid 11 and the retaining wall 49. As soon as the water level rises, the retaining wall 49 is pivoted anti-clockwise by the float 51, and water can rise and pass through the grid 11 into the space 37. Water flows through at this point until the space 37 is filled. Only when the water level in the relief channel reaches level hl do.es a continuous throughflow begin i.e. the continuous water throughflow with the impurities, which are already partly held back at the retaining wall 49 is only ef f ected when the entire grid surf ace is in contact with the water. Thus there is a uniform distribution of the impurities 61 held back on the grid 11. During the waiting period of the water f lowing through in space 37, impurities which have been able to pass through the grid 11 can be deposited at this point. The deposited impurities 61 slide on the bottom portions 39 to the backpressure flap 41, where they are retained. When water is overflowing above level hi, the backpressure f lap 41 or its lid 43 is closed, as it is held in a closed position by the static pressure of the water in the relief channel 5.

If the water in the relief channel rises substantially above level hl, it can escape, albeit unpurified, over he overflow bridge 25 out of the relief channel 5. In this case the space 37 is not filled with impurities 61.

As soon as the water supply in the relief channel 5 drops back, i.e. the water level drops below level hl, no further water can escape over the retaining wall 31. As soon as the water level drops below the height of the backpressure flap 41, the lid 43 opens and the impurities 38 deposited on the bottom portions 39 are passed along with the water likewise held back at that point through the now open backpressure flap 41, back into the relief channel 5 and from that point to a sewage treatment installation. The method of operation of the embodiment of the invention shown in Fig. 3 differs only in that the retaining wall 55 slides vertically upwards as the water rises in the relief channel 5, thus enabling water to pass through the grid 11. As long as only a small level of retained water is present, the float 51 is not raised, and therefore no impurities, contacting only the lower r j, area of the grid 11, can pass through. The full operation of the grid 11 here also begins only when the water has reached level hi (position of the retaining wall 57 in broken lines).

The lids 43 of the backpressure flaps 41 could also alternatively be opened or closed by an electrical or pneumatic drive system. In-this way, when the water level in the relief channel is dropping, a larger proportion of water could be held back in the tanks 45, and then suddenly emptied, so that the impurities 38 collected at that point could be washed away by a powerful rush of water.

- The drive system for the comb 21 may be disposed directly above the grid 11 in a channel 14, and can comprise a linear drive (pneumatic cylinder, hydraulic cylinder of electrically drive means) (cf. Fig. 3).

Instead of or in addition to the comb 21 described in Fig. 4, cleaning of the grid 11 can be effected by a sprinkler installation 63 or a spray nozzle arrangement, mounted in space 37. The sprinkler installation 63 can also be used for cleaning the tank 45.

Instead of grid bars 13 mounted in framework 15, tensioned wire ropes could be used (not illustrated).

Claims

1. A grid arrangement for rain overflow tanks, flood relief installations and the like having grids comprising rods or ropes disposed parallel to one another and next to one another and attached by their ends to a framework, said grids being mounted on an overflow wall, and whose through-passage surface, acting as a grid, is disposed at an angle of from 450 to 900 to the horizontal, and having a retaining wall for raising the retained level to the level of the upper edge of the grid, in which the bottom portions defining at the foot the space formed by the grid and the retaining wall are disposed to be included at an acute angle to the grid bars or ropes, and are connected at their lowest point with a backpressure flap leading into the relief channel.

2. A grid arrangement as claimed in claim 1, in which the lower region of the space is in the form of a tank which is adapted to be mounted or embedded on the crown of the overflow wall.

3. A grid arrangement as claimed in claim 1 or 2, in which the bottom portions of the tank are also adapted to incline downwards in the direction of the relief channel

4. A grid arrangement as claimed in claim 1, 2 or 3, in which a retaining wall is attached on the inlet side of the grid, which wall is vertically adjustable by means of a float and/or an electrical drive system.

5. A grid arrangement as claimed in claim 4, in which the retaining wall is pivotal about a horizontal axis, or in which the retaining wall is vertically displaceable in a guide.

1 1

6. A grid arrangement as claimed in any preceding claim, in which an overflow bridge for deflecting water above the space is disposed above the grid.

7. A grid arrangement as claimed in claim 6, in which the overflow bridge has a vertical portion continuing from the upper edge of the grid, and a horizontal portion, both said portions being fixed or displaceable and adjustable in their height or length.

8. A grid arrangement as claimed in any preceding claim, in which a sprinkler installation of a spray nozzle for cleaning the grid and/or the bottom portions is disposed in the space.

9. A grid arrangement as claimed in any preceding claim, in which a comb is disposed in a travelling manner parallel to the grid in order to clean the latter.

10. A grid arrangement as claimed in any preceding claim, in which the drive system for the grid is disposed in a channel mounted on the upper edge of the grid.

11. A grid arrangement for rain overflow tanks, flood relief installations and the like, substantially as hereinbefore described with reference to the accompanying drawings.