GB2310382A

GB2310382A - A sewage screen

Info

Publication number: GB2310382A
Application number: GB9702967A
Authority: GB
Inventors: David Peter Froud
Original assignee: Apoc Ltd
Current assignee: Apoc Ltd
Priority date: 1996-02-23
Filing date: 1997-02-13
Publication date: 1997-08-27
Anticipated expiration: 2017-02-13
Also published as: GB9603880D0; GB2310382B; GB9702967D0

Abstract

A sewage screen 14 defines at least one pocket 48 extending downstream of at least some portion of the screen 14 to accommodate inorganic debris. The screen 14 is recessed by having generally horizontally extending slat portions located downstream of a main part of the screen which consists of horizontally extending slat portions 40 in a central region of the screen. The screen 14 further comprises slat portions 42 extending outwardly and upwardly from the central slat portions 40. The slat portions 42 are then connected to axially extending dividing walls 44. Horizontally extending slat portions 46 extend from the upper edges of the dividing walls 44 to the walls of a shaft 12 (overflow channel). The above construction generally forms the shape of an inverted top hat. The region within the shaft interior bounded by the dividing walls 44, the slat portions 46 and the walls of the shaft 12 constitute pockets 48. Rake tines 32 are moved to and fro along the slats 40 of the screen 14 to clear debris trapped between two adjacent slats. The screen is disposed in an overflow channel which extends upwardly from a sewage conduit 10. Alternative pocket constructions are possible in which the shape of the screen and shaft differ from the above construction (Figs 4-10).

Description

A sewage screen The present invention relates to a sewage screen.

An example of such a screen, installed as part of sewage storm overflow equipment, is shown in Figures 1 and 2 in which Figure 1 shows an axial sectional diagrammatic view of the equipment; and Figure 2 shows a plan view thereof.

With reference to Figures 1 and 2, a sewage discharge conduit 10 is provided with an upwardly extending storm overflow shaft 12, the interior of the latter being in communication with the interior of the conduit 10.

A screen 14 extends horizontally across the upwardly extending shaft 12. It comprises a frame 16 across which a multiplicity of parallel slats 18 extend with generally uniform spacings between one slat and the next. Suitable retaining means (not shown) may be provided to hold the frame 16 in place in the shaft 12, for example bolts or shoulder portions provided on the interior surface of the shaft 12.

Arranged above the top of the storm overflow shaft 12 is a rake assembly 20 comprising two parallel guide rails 22 positioned to opposite sides of the shaft 12 and both extending parallel to the slats 18 and in a generally horizontal direction, a pneumatic or hydraulic drive 24 from which extends one or more drive rods 26 extending midway between and parallel to the guide rails 22, and two pairs of connecting rods 28 extending horizontally and generally at right angles from the rods 26 to sliding bearings 30 supported on the guide rails 22. A multiplicity of downwardly extending mutually parallel tines 32 are spaced apart uniformly along and connected at their upper ends to the connecting rods 28. At their lower ends, the tines 32 interengage the slats 18.Thus each pair of rods 28 and their associates tines provide a rake so that there are two rakes in this embodiment each with a series of tines 32. Each rake has one tine for every gap between two adjacent slats 18. Respective bars (not shown) may extend horizontally below the screen 14, interconnecting the bottom ends of the respective series of tines 32 of the two rakes.

In normal weather conditions the sewage flows through the conduit 10 in the direction shown by the arrow therein.

Whilst the sewage conduit 10 may be part of a combined sewage system (not shown) which can cope with up to six times the flow rate encountered in dry weather conditions, in the event of a storm with which even the combined sewage system cannot cope, fluid from the sewage conduit 10, which now comprises storm water as well as raw sewage can discharge upwardly through the storm overflow shaft 12.

The screen 14 acts as a barrier to trap inorganic debris such as plastics, sanitary ware, and rags which are not readily biodegradable and which should not therefore be released from the overflow shaft 12, whilst at the same time allowing water and faecal material to pass through.

Operation of the drive 24 moves the tines 32 to and fro along the slats 18 of the screen 14, via the connecting rods 28 and drive rods 26. As a result, the passageway available for flow of fluids through the screen 14 is maintained.

A problem encountered with such overflow equipment is that the inorganic debris can become compacted against the screen 14, under considerable upward force, the upward flow through the overflow shaft 12 driving the debris against the screen in an upward direction. After a while, it is possible for the compacted debris to accumulate to such an extent that the flow of fluid through the overflow shaft 12 is inhibited. In extreme circumstances this could cause undesirable flooding and release of unscreened sewage elsewhere in the system.

It is an aim of the present invention to obviate this disadvantage.

Accordingly the present invention is directed to a sewage screen having at least one pocket extending downstream of at least some portions of the screen, in relation to an intended direction of flow, to accommodate inorganic debris.

In one preferred embodiment of the invention, at least one portion of the screen itself is recessed, viewing the latter from a position upstream thereof, to provide such a pocket. This provides the advantage that such a screen may be made so that it can readily replace a conventional fluid screen such as is shown in Figures 1 and 2, without changing any other part of the equipment shown in those Figures. Such a screen embodying the present invention can therefore be used in existing installations.

In one possible such construction of screen, generally horizontally extending slat portions are located downstream of a main part of the screen constituted by horizontally extending slat portions in a central region of the screen. In this way, the screen may have an inverted top hat cross section.

The slat portions constituting the main part of the screen may be connected to those which are located downstream thereof by dividing walls. Alternatively they may be so connected by further slat portions whereby the tines may be moved all the way to the outer edges of the screen, without retracting them or changing their vertical level.

Slat portions may slant upwardly from ends of slat portions constituting a main central part of the screen, in a downstream and outward direction. This may be in addition to or instead of the presence of the rearwardly positioned horizontally extending slat portions.

The pockets may instead be provided by concave arcuate slat portions at the ends of slat portions constituting a main central part of a screen, viewing the screen from an upstream position.

The present invention extends to sewage storm overflow equipment, comprising a sewage conduit, an overflow shaft extending upwardly from the sewage conduit and connected thereto in such a manner that the interior of the conduit is in communication with the interior of the overflow shaft, and a screen extending across the overflow shaft and having at least one pocket extending downstream of at least some portions of the screen to accommodate inorganic debris.

The pockets may be defined by portions of the shaft extending outwardly of and around the screen.

A pipe may extend downwardly (upstream) from the or each pocket to the interior of the sewage conduit so that a down-current is created within the pipe when the storm overflow equipment is in use, to draw inorganic debris downwardly from the or each pocket and return it back to the main sewage flow.

Examples of sewage screens embodying the present invention will now be described with reference to Figures 3 to 9 of the accompanying drawings in which Figure 3 shows an axial sectional diagrammatic view of sewage storm overflow equipment incorporating such a screen; Figures 4 to 7 show respective sectional views of portions of modified screens embodying the present invention; Figure 8 shows an axial sectional diagrammatic view of modified storm overflow equipment embodying the present invention; Figure 9 shows an axial sectional diagrammatic view of a modification of the configuration shown in Figure 8; and Figure 10 shows an axial sectional diagrammatic view of a further construction of storm overflow equipment embodying the present invention.

The equipment shown in Figure 3 comprises many parts illustrated in Figures 1 and 2, and corresponding parts bear the same reference numbers as in those Figures.

The equipment shown in Figure 3 differs from that shown in Figures 1 and 2 in that one of the rakes has been omitted, so that the remaining rake can sweep all the way from one side of the screen to the other, so reducing the likelihood of debris accumulating in central regions of the screen.

The equipment shown in Figure 3 more importantly differs from that shown in Figures 1 and 2 in the construction of the screen 24. Instead of the flat generally uniplanar construction shown in Figures 1 and 2, the screen 14 in the construction shown in Figure 3 has a cross-section which is generally of the shape of an inverted top hat. Thus it has a series of parallel generally horizontally extending slat portions 40 constituting a main central portion of the screen, with slanting slat portions 42 extending outwardly and upwardly (outwardly and rearwardly with respect to the intended upward direction of flow of fluid in the shaft 12) from the ends of the central shaft portions 40. The outer ends of the slanting portions 42 are connected to axially extending dividing walls 44.Lastly, generally horizontally extending slat portions 46 extend from the upper edges of the walls 44 to the walls of the shaft 12.

It will be appreciated that for each and every central slat portion 40 there are two slanting portions 42 and two outer end portions 46 all in the same plane as the central slat portion 40.

It will be seen that the regions within the shaft interior bounded by the dividing walls 44, the slat portions 46 and the walls of the shaft constitute pockets 48 in which inorganic debris can be accommodated.

Under storm conditions, with a surge of fluid flowing upwardly through the overflow shaft 12, to and fro movement of the tines 32 maintains the through-flow through the apertures between the slats. Any inorganic debris trapped on the underside of the main central portion of the screen will be shifted outwardly by one or other of the rakes to the slanting slat portions 42 where the upward flow of the fluid will carry the debris into the pockets 48.

When the storm subsides and the water level in the shaft 12 drops, the inorganic debris falls with it and in the end is received back into the sewage conduit 10.

In this way inorganic debris is prevented from being released to the environment whilst at the same time is not allowed to prevent adequate through-flow of fluid up through the overflow shaft 12.

In the modification shown in Figure 4, there are no slanting portions 42, so that the central slat portions 40 extend all the way up to the walls 44. The width of the slats 40 extends downwardly from the bottom edge of each wall 44 so that the rakes can more easily clear debris trapped between two adjacent slats.

In the modification shown in Figure 5, the dividing walls 44 are replaced by axially extending slat portions 50 in the same plane as respective associated central slat portions 40 and rearwardly positioned slat portions 46. This increases the overall flow capacity of the screen 14.

In the modification shown in Figure 6 the slanting portions 42 extend all the way to the walls of the shaft 12, so that the dividing walls 44 and the slat portions 46 are omitted altogether.

In the form shown in Figure 7 the slanting slat portions 42 are replaced by arcuate slat portions 52, which are concave when viewed from an upstream position of the screen.

The modification shown in Figures 5, 6 and 7 each have the advantage that the rake tines 32 can move along the screen all the way to the extreme edges thereof where it meets the side walls 12 of the overflow shaft.

The equipment shown in Figure 8 is provided with a screen having the construction shown in Figure 6.

In addition, it is provided with two down pipes 54 which have upper flared ends 56 located in the vicinity of the pockets 48 and lower ends 58 which extend into the interior of the conduit 10 where they turn through a right angle so that they extend in an axial direction with respect to that conduit. The bottom ends of the down pipes 54 are adjacent to one another at a position in the conduit 10 which is downstream of the shaft 12, in relation to the flow in the conduit 10. This improves the downy low through the down pipes 54 by taking advantage of the differential pressure head between the fluid in line with the shaft 12 and that in the conduit 10.

When this equipment is in use, the flow within the sewage conduit 10 draws fluid downwardly from the pipes 54 thus urging inorganic debris collecting in the pockets 48 back into the main sewage flow.

In the modification to the construction of Figure 8, shown in Figure 9, the slats of the screen 40, and hence the direction in which the pockets 48 are displaced from one another, is substantially at right angles to the direction of flow of fluid through the conduit 10. The horizontal end portions 58 of the down pipes 54 can then be of substantially the same length, whilst still terminating at positions about the same distance downstream of the shaft 12 as one another. This improves the symmetry of flow and the strength of the down flow.

In the construction shown in Figure 10, the screen 14 has a flat and generally uniplanar portion extending all the way across the shaft 12 as in the construction shown in Figures 1 and 2. The shaft walls 12 construction shown in Figures 1 and 2. The shaft walls 12 however extend outwardly around the ends of the screen 14 at portions 60 thereof to define pockets 48 which extend from a position upstream of the screen 14 to a position downstream thereof. The boundary of the pockets 48 at their downstream end are defined by slat portions 62 extending upwardly from both ends of each horizontal slat, to allow fluid to flow through the pockets 48 back into the shaft 12 at a position downstream of the screen 14. This therefore retains the ability of the rake tines 32 to tip inorganic debris into the pockets 48.The tines 32 may be provided with widened bottom portions 64 which poke through the gaps between the slat portions 62 when the tines 32 are at their extreme ends of travel, and hence maintain clear passageways for fluid through the portions 62.

Numerous modifications to the illustrated apparatus will readily occur to a person of ordinary skill in the art without taking the modified construction clear of the present invention. For example the central slat portions 40 may be generally angled in relation to the shaft 12. The angle of slant of the slat portions 42 may be substantially anywhere in the range from 10 to 900.

Instead of having two pockets 48 at the ends of the screen, there may be one centrally positioned pocket, in which case two rakes would be provided as in the construction illustrated in Figures 1 and 2.

The screen shown in Figure 8 could be modified by omitting the horizontally extending slat portions and having longer slanting portions 42 which are joined centrally in relation to the shaft 12, so that the screen 14 generally has a V cross section, the tines 32 also being longer to reach the lowermost portions of such a modified screen.

Claims

Claims :

1. A sewage screen having at least one pocket extending downstream of at least some portions of the screen, in relation to an intended direction of flow, to accommodate inorganic debris.

2. A sewage screen according to claim 1, in which at least one portion of the screen itself is recessed, viewing the latter from a position upstream thereof, to provide such a pocket.

3. A sewage screen according to claim 2, in which the screen is recessed by having generally horizontally extending slat portions located downstream of a main part of the screen constituted by horizontally extending slat portions in a central region of the screen.

4. A sewage screen according to claim 3, in which the slat portions constituting the main part of the screen are connected to those which are located downstream thereof by at least one dividing wall.

5. A sewage screen according to claim 3, in which the slat portions constituting the main part of the screen are connected to those which are located downstream thereof by further slat portions whereby rake tines may be moved all the way to the outer edges of the screen, without retracting them or changing their vertical level.

6. A sewage screen according to any preceding claim, in which slat portions slant upwardly from ends of the slat portions constituting a main central part of the screen, in a downstream and outward direction.

7. A sewage screen according to claim 2, in which the pockets are provided by concave arcuate slat portions at the ends of slat portions constituting a main central part of a screen, viewing the screen from an upstream position.

8. Sewage storm overflow equipment, comprising a sewage conduit, an overflow shaft extending upwardly from the sewage conduit and connected thereto in such a manner that the interior of the conduit is in communication with the interior of the overflow shaft, and a screen extending across the overflow shaft and having at least one pocket extending downstream of at least some portions of the screen to accommodate inorganic debris.

9. Sewage storm overflow equipment, comprising a screen as claimed in any one of claims 2 to 7.

10. Sewage storm overflow equipment according to claim 8, in which the or each pocket is defined by portions of the shaft extending outwardly of and around the screen.

11. Sewage storm overflow equipment according to any one of claims 8 to 10, further comprising a pipe extending downwardly from the or each pocket to the interior of the sewage conduit so that a down-current is created within the pipe when the storm overflow equipment is in use, to draw inorganic debris downwardly from the or each pocket and return it back to the main sewage flow.

12. A sewage screen substantially as described with reference to and as illustrated in any one of Figure 3 to 9 of the accompanying drawings.

13. Sewage storm overflow equipment substantially as described with reference to and as illustrated in any one of Figures 4 to 9 of the accompanying drawings.