GB1598103A - Apparatus for clearing screens such as storm water overflow screens - Google Patents

Description

(54) APPARATUS FOR CLEARING SCREENS, SUCH AS STORM WATER OVERFLOW SCREENS (71) We, LONGWOOD ENGINEERING COMPANY LIMITED, a British Company, of Parkwood Mills, Longwood, Huddersfield, HD3 4TP, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to apparatus for clearing screens, such as storm water overflow screens, or general screens as used in water or other works and applications.

The general type of screens to which the invention relates are those whose function it is to stop the flow of debris and other solid objects and material referred to herein collectively as debris, being carried along in a flow of liquid, from passing the screen, which in effect filters out the debris from the flow.

In sewage installations in storm conditions, these screens are particularly relevant because the sewage flow increases beyond what sewage installations can process and it is necessary to bleed off some of the water, filter it and discharge it for example into streams or rivers. It is of course necessary that debris should not be discharged along with this water bled off.

The screen cleaning apparatus usually comprises a rake which is swept across the screen to remove collected debris from the screen and suitably return it to the normal flow channel. The rake is usually carried by rake gear and may be swept in a linear path over a flat screen or in a curved path over a curved screen. The screen conventionally is a plurality of bars arranged parallel and the rake has teeth or tines which pass between the parallel screen bars.

It sometimes happens that a piece of debris, such as a branch of a tree or a stone, will become wedged between a pair of the screen bars so firmly as not to be displaceable by the rake, or at least not by a single pass of the rake. To avoid damage to the rake and to the drive thereof in such circumstances, it is known to arrange for the whole of the rake and its mounting to yield away from the screen when the rake encounters such obstructions.

A disadvantage of this arrangement is that when the rake yeilds away from the screen, none of the screen swept by the rake is cleaned, and if the rake yeilds away from the screen at each pass, none of the screen will be cleared until the obstruction is otherwise removed.

The present invention aims to overcome this difficulty and in accordance with the invention there is provided an apparatus for clearing screens for filtering debris from a flow of liquid which passes through the screen leaving the debris behind, comprising rake gear having an elongated rake adapted to sweep over the screen to clear debris therefrom, said rake being in two or more aligned sections which are associated with yield able loading means for holding the sections in raking engagement with the screen each of said sections being individually yieldable against the loading means from a raking position to a non-raking position in the event of that section of the rake meeting an obstruction on the screen which offers greater resistance than the loading of the loading means.

It will be appreciated that with such arrangement if there is an obstruction which causes displacement of one of the rake sections, the other rake section can continue sweeping the other portion or portions of the screen.

The rake is preferably in three sections, and each of said sections is mounted for pivotal movement between said positions, the yieldable loading means comprising a coiled spring, one for each section, lying around a pivot pin defining the axis of pivoting of that section.

The raking gear may comprise one or more rotary assemblies, each comprising one or more diametral arm pairs, each having two rake mounting bars at diametrically opposite locations relative to, and equidistant from the axis of rotation of the assembly, each of said bars having a said rake in three sections, such sections being pivotally mounted on the bars as aforesaid. Where two of such assemblies are provided and each has one diametral arm pair the assemblies are preferably arranged to rotate about a common axis, but spaced axially of said axis, and lying respectively in planes which are at 90 to one another.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, wherein: Fig. I is a sectional end rear view of a water stilling chamber of a sewage installation provided with screen clearing apparatus according to the embodiment of the invention; Fig. 2 is a sectional elevation of the chamber shown in Fig. 1, taken on the line I-I of Fig. I; Fig. 3 is an elevation of one of the rake sections of one of the rakes of the apparatus shown in Figs. 1 and 2: Fig. 4 is a sectional elevations on an enlarged scale of the rake section shown in Fig. 3; and Fig. 5 is a central sectional end elevation of the rake section shown in Figs. 3 and 4.

A water stilling chamber of a sewage installation is shown in Figs. I and 2 and will be seen to comprise concrete housing 10 which is entered by a flow channel 12 along which sewage flows into the housing, and in normal conditions the sewage flows out through a discharge pipe 14 for further processing.

A moulded channel 16 of U-configuration in section extends across the width of the housing 10 and has an inclined bottom leading downwardly to a storm water outlet pipe 10 as shown in Fig. 2.

Above the channel 16 is placed a curved screen of conventional construction comprising a plurality of curved, equally spaced and parallel bars 22 as shown in Fig. 2. The screen is cleared by two rake assemblies which clean respective halves of the screen, which is in fact arranged in two bays respectively for said rake assemblies. Each rake assembly comprises diametral arm pairs 24 rotatable about an axis defined by a common whaft 26, and thearms 24 carry rake support bars 28 at diametrically opposite locations relative to and at equal distances from the shaft 26. Such bars 28 carry rakes 30 which in this example have teeth which pass between the bars 22 as each rake 30 sweeps across screen 20.In storm conditions, the level of liquid in channel 12 rises sharply and the water flows over into discharge pipe 18 through the screen, leaving debris behind on the screen, the water passing along pipe 18 being discharged for example to a stream or river. The rakes serve to clear the screen of the debris which is left on the screen and to discharge it into benching 32 from whence it passes back into the flow along pipe 14 for further processing.The driving motor 34 for the rake assemblies is provided in a subchamber as shown in Fig. 2 and the arms 24 of the respective rake assemblies are arranged in planes which are at 90 to one another The apparatus thus far described basically is known, but in accordance with the embodiment of the present invention, the rakes 30 are arranged in sections as will now be described with reference to Figs. 3 to 5. In this example, each rake is arranged in three sections which are independantly pivotable.

If reference is made to Fig. 3, one of the radial arms 24 of the relevant rake assembly is shown and the rake section illustrated is indicated by reference numeral 30A. For the rake section 30A, the bar 28, which is an angle iron as shown in Fig. 5, is provided with a pair of mounting brackets 34' mounting a shaft 36 on which are pivotally mounted rake brackets 38 through bearings 40, the rake brackets 38 being welded to the rake plate 42. The rake has teeth 44 which pass between the bars 22 of the screen 20.

Fig. 3 shows the relative position of the next adjacent rake section 30B and it is to be noticed that the first tooth on section 30B and the last tooth on section 30A are separated by the same pitching as are the teeth 44 of the section 30A, and indeed each of the rake sections, so that the whole screen will be effectively swept.

Surrounding the shaft 36 is yieldable loading means in the form of a coiled spring 46, having one end 46A bearing against the plate 42 to urge it to pivot in an anticlockwise direction in Fig. 5, and another end 46B bearing on the underside of one of the limbs of the bar 28. By this arrangement the coiled spring which is tensioned forces the plate 42 against the other limb of the bar 28 and this is the normal position which the plate takes up and is referred to as the raking position.

If reference is made to Fig. 5, the rake section 30A is arranged to sweep over the screen in the direction of arrow 50, and normally the spring force applied by spring 46 will maintain the plate 42 in that position.

However, if the plate meets an obstruction which provides a greater resistive force than the spring force of spring 46, the plate 42 can deflect away against the spring action in the direction of arrow 52 and may reach a position for example indicated in dotted lines in Fig. 5 in order not to damage the rake gear. If the obstruction interferes with the operation of only section 30A, then the other sections of the rake can continue raking normally and even if the obstruction has to be removed subsequently by other means, at least 2/3rds of the screen will continue to be cleared as normal, which is different from the known arrangement in which the whole of the rake is deflected upon meeting an obstruction.

It is appreciated that other arrangements may be provided for arranging for the rake sections to retract differently from that shown in the drawings, and it is also to be appreciated that the invention can be applied to rakes which move linearly as opposed to those which move in a rotary manner as the example given herein.

WHAT WE CLAIM IS: 1. An apparatus for clearing screens for filtering debris from a flow of liquid which passes through the screen leaving the debris behind, comprising rake gear having an elongated rake adapted to sweep over the screen to clear debris therefrom, said rake being in two or more aligned sections which are associated with yieldable loading means for holding the sections in raking engagement with the screen each of said sections being individually yieldable against the loading means from a raking position to a nonraking position in the event of that section of the rake meeting an obstruction on the screen which offers greater resistance than the loading of the loading means.

2. An apparatus according to Claim 1, wherein each of said sections if mounted for pivotal movement between said positions, the yieldable loading means being a coiled spring, one for each section, lying around a pivot pin defining the axis of pivoting of that section.

3. An apparatus according to Claim 1 or 2, wherein the rake gear comprises one or more rotary assemblies, each comprising one or more diametral arm pairs, each having two rake mounting bars at diametrically opposite locations relative to, and equidistant from the axis of rotation of the assembly, each of said bars having a said rake in three sections.

4. An apparatus according to Claim 3, wherein there are two of said assemblies and each has one diametral arm pair, and the assemblies are arranged side by side for rotation about a common axis and the radial arms of one lying in a plane at 90 to the plane of the radial arms of the other 5. An apparatus for clearing screens sub stantially as hereinbefore described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. may be provided for arranging for the rake sections to retract differently from that shown in the drawings, and it is also to be appreciated that the invention can be applied to rakes which move linearly as opposed to those which move in a rotary manner as the example given herein. WHAT WE CLAIM IS:

1. An apparatus for clearing screens for filtering debris from a flow of liquid which passes through the screen leaving the debris behind, comprising rake gear having an elongated rake adapted to sweep over the screen to clear debris therefrom, said rake being in two or more aligned sections which are associated with yieldable loading means for holding the sections in raking engagement with the screen each of said sections being individually yieldable against the loading means from a raking position to a nonraking position in the event of that section of the rake meeting an obstruction on the screen which offers greater resistance than the loading of the loading means.

2. An apparatus according to Claim 1, wherein each of said sections if mounted for pivotal movement between said positions, the yieldable loading means being a coiled spring, one for each section, lying around a pivot pin defining the axis of pivoting of that section.

3. An apparatus according to Claim 1 or 2, wherein the rake gear comprises one or more rotary assemblies, each comprising one or more diametral arm pairs, each having two rake mounting bars at diametrically opposite locations relative to, and equidistant from the axis of rotation of the assembly, each of said bars having a said rake in three sections.

4. An apparatus according to Claim 3, wherein there are two of said assemblies and each has one diametral arm pair, and the assemblies are arranged side by side for rotation about a common axis and the radial arms of one lying in a plane at 90 to the plane of the radial arms of the other

5. An apparatus for clearing screens sub stantially as hereinbefore described with reference to the accompanying drawings.