GB2202465A

GB2202465A - Liquid treatment apparatus

Info

Publication number: GB2202465A
Application number: GB08812193A
Authority: GB
Inventors: Anthony John Butwell
Original assignee: Water Research Centre
Current assignee: Water Research Centre
Priority date: 1985-04-03
Filing date: 1988-05-23
Publication date: 1988-09-28
Also published as: GB8508693D0; GB2173128A; GB2202465B; GB2173128B; GB8812193D0

Abstract

A hollow distribution arm (200) for a water filtration plant (e.g. a percolating filter) has a series of jets (204) disposed along the arm to deliver liquid (to be filtered) from within the arm on to the filter bed (202). To prevent the jets blocking, plungers (210) are mounted on the arm (one plunger for each jet) by support members (207), and are periodically moved into their respective jets to clear obstructions therein. Each support member has a region of flexure defining an axis about which the plunger pivots. Conveniently, the support member is fixed to the arm at the jet itself. Preferably, the support member 207 is a strap moulded integrally with a body portion 209 from which the plunger projects. <IMAGE>

Description

LIQUID TREATMENT APPARATUS This invention relates to a liquid treatment apparatus and, more particularly, to distributor arms utilised in filtration plant.

Percolating filter plants for the treatment of aqueous effluents such as sewage are well known. They comprise a filter bed and a series of hollow liquid distributor arms disposed horizontally over the bed and mounted on a vertical shaft centrally of the bed. The shaft is rotated to niove the arms to distribute the liquid over the bed from jets disposed in the distributor arms. One problem with these known arrangements is that the jets tend to clog up which results in an uneven distribution of the liquid over the filter. The jets have to be cleaned manually.

To alleviate this problem, removable screens are sometimes installed in channels conveying primary tank effluent, but these too usually need clearing at least daily, and the screenings have to be disposed of.

It has been proposed to deal with this problem of jet blockage by providing, adjacent each jet, a plunger which intermittently is operable to enter the jet to clear any blocking debris. In one known arrangement, the plungers are mounted on a common axle and the axle is caused to turn to move the plungers into their respective jets, and to return (to remove the plungers) by engagement of a lever with a trip mechanism. Thus, as the arm moves above the filter bed, the lever rides up over a trip and then returns to its starting position.

There are a number of problems with this known arrangement. Firstly, it can be difficult to install a series of plungers on a common axle, so that each plunger is precisely oriented to enter its respective jet. Also, after installation, mis-alignment can occur which can damage the device and also jam movement of the distributor arms themselves. Further, the installation is complex and relatively expensive.

With a view to reducing or overcoming these problems, we have proposed in our U.K. patent specification no. 2143154A a distributor arm in which each jet has associated therewith a bracket mounted externally on the arm, which bracket pivotally supports a plunger movable into and out of the jet to keep it clear of obstructions.

Thus, instead of having all the plungers on each arm mounted on a common axle, they are individually pivotally mounted, each on an individual brakcet attached to the distributor arm. In this way, the alignment problems of the common axle arrangements, and the overall complexity of such arrangements, are reduced or overcome.

The particular embodiments of Figures 5 to 7 of U.K. specification no. 2143154A do, however, occasionally give rise to another, different problem. In these embodiments, rigid brackets extend from the distributor arm at each jet, and the plunger (itself usually mounted on an adjustable support for initial alignment with the respective jet) is pivotally mounted to the bracket. In extremely cold weather, water on the pivot will freeze during the time interval between successive actuations of the plunger, so jamming the plunger and preventing further actuation of it. This, in turn, means not only that the respective jet will not be cleared of obstructions but also that the distributor arm itself may become jammed, so dislocating operation of the whole filter unit.

We have now found that this problem can be overcome and that certain other advantage can be achieved over the designs shown in U.K. specification 2143154A.

In accordance with one preferred feature of the present invention, the individual plungers are each mounted with respect to the distributor arm by a support member which has a flexure region. Thus, during movement of the plunger (for its passage into and out of the respective jet) pivoting occurs by flexure of the support member at its flexure region (and not at a hinge formed on a rigid member). The preferred support member is a strap of plastics or other synthetic material (eg. a synthetic rubber such as EPDM).

The whole of the support member can be flexible, but it is then usually necessary to confine flexure to one particular region to define the pivot axis of the plunger (to ensure that the plunger repeatedly and reliably enters its respective jet). Flexure can be confined to one particular region by, for example, applying a stiff plate over that part of the support member where flexure is not required. Alternatively,in another example, the support member may itself be fairly rigid or stiff except at the flexure region, which region can for example be formed by localised thinning of the member (eg. strap).

One end of the support member is attached to the distributor arm. Preferably, the same arrangements are used here as are described in our specification no.

2143154A, i.e. the support member is attached to the arm using a flanged nozzle screw-threadedly received in an orifice in the arm. Reference should be made to our said specification no. 2143154A for further details. Whilst such arrangements are preferred, they are not essential.

We prefer that the plunger be mounted in a body which is attached to the end of the support member.

Most preferably, the body and support member together are a one-piece moulding, the body portion preferably being moulded around one end of the plunger to locate it therein.

In preferred arrangements of the present invention, the plunger units (i.e. support member/body/ plunger) are relatively maintenance free in use. When one-piece mouldings are used, the units are of very simple construction and yet of long life. In the unlikely event of failure of a unit, it can easily be replaced, and each unit is of relatively low cost.

It is, of course, very important that the units be so arranged that the plunger will be correctly aligned with the respective jet. We have found that this can be achieved even using flexible support member. Thus, for example, in the case of a strap-like support member, we have found that it should preferably have a greater width than thickness, to prevent any significant twist.

The achievement of the optimum arrangement with any particular plunger unit will normally require some routine trial and experiment, but this will be well within the ability of the skilled man.

In order that the invention may be more fully understood, one embodiment thereof will now be described, by way of example only, with reference to the accompanying drawings wherein: Figure 1 illustrates a percolating filter with distributor arms; Figure 2 is a view of a distributor arm of a percolating filter, the arm being fitted with plunger units in accordance with the present invention; and Figure 3 is a section of the arm of Figure 2.

Reference is made to the drawings and description in our U.li. specification no. 2i43154A for a description of prior proposals.

Referring to the drawings, Figure 1 illustrates one form of percolating filter 100. This arrangement has four hollow distributor 102,103,104,105 arms extending radially outwards from a supporting upright supply pipe 106 which supplies liquid (to be filtered) to each arm.

Pipe 106 carries an upward extension 107 from which guy ropes, spars or the like 108 extend to support the arms 102,103,104,105. The filter bed 109 is formed between a circular inner wall 110 and a circular outer wall 111 and extends into the ground Illa (the below-ground arrangements are not shown).

The outer end of each hollow arm 102,103,104,105, is closed by a plate 112, but each arm has a series of orifices 113 spaced along its length. The orifices may have jets or nozzles mounted therein. In use, the liquid to be filtered issues from the arms through the orifices and on to the filter bed 109. The supply pipe 106, extension 107 and the four arms 102,103,104,105, are slowly rotated in the direction of arrow 114 so that t arms sweep over the whole of the filter bed surface to distribute the liquid thereover.

Figure 1. thus illustrates a percolating filter with distributor arms.

Referring now to Figures 2 and 3, there is shown a distributor arm 200 (mounted on a supply riser 201) and extending over a filter bed surface 202. The inner filter wall 203 is also shown (in part). The arm 200 has a series (only four illustrated) of jets 204 therein each comprising a flanged nozzle 205 screwed into an orifice 906 in the arm 200. Each flanged nozzle 205 passes through the end portion of a strap member 207 and reinforcing plate 208. The strap 207 has a generally segment-shaped body 209 attached to its lower end, and from body 209 projects plunger 210. In practice, strap 207 and body 209 are preferably a one-piece plastics or elastomeric (eg. EPDM) moulding formed around the end of plunger 210.Reinforcing plate 208 lies flat against strap 207 over its upper portion, but plate 208 stops short of body 209 and in the region "X" between body 209 and the lower end of plate 208, the strap 207 has a flexing area, i.e. it is free to flex. Flexure about a horizontal axis in this area permits body 209 and plunger 210 to swing upwards and enter nozzle 205 when body 209 rides up over a trip bar 211 laid on the filter surface.

Strap 207 is of rectangular section and has a greater width than thickness. This helps to ensure that the plunger 210 will be correctly positioned to enter its respective nozzle 205. Body 209 includes a spacer 212 which controls the depth to which the plunger 210 penetrates into the distributor arm 200 through a nozzle 204.

The self-cleaning mechanisms of the invention for the jets of distributor arms are especially useful in the biological filtration of finely-screened sewage using highvoidage plastics filter elements. The sewage to be treated is finely-screened to remove only the large ,materials, and is then distributed over a bed of the filter elements using distributor arms fitted with the cleaning mechanisms of the present invention.

As will be understood by those skilled in the art, various modifications can be made to the arragement illustrated. For example, a continuous trip bar 211 need not be used. Individual trip projections (upstanding from the filter bed) can be used to trip individual plunger units or groups of two or more thereof, simultaneously or at predetermined time intervals.

Claims

CLAIMS:

1. A hollow distributor arm for a filtration plant, which arm comprises a plurality of jets mounted therein to distribute liquid, supplied through said arm, over a filter, wherein each jet has associated therewith a plunger movable into and out of said jet to keep the same clear of obstructions, and wherein each said plunger is mounted with respect to the distributor arm by a support member having a region of flexure defining a pivot axis of the plunger so that, during movement of the plunger into and out of the jet, pivoting occurs at the flexure region of said support member.

2. A distributor arm according to claim 1, wherein each support member is mounted on the arm by engagement thereof with a respective jet.

3. A distributor arm according to claim 2, wherein each jet comprises a cylindrical body having an external flange at one end the said body passing through a hole in said support member and being secured to said arm with said flange engaging said support member to mount it on said arm.

4. A distributor arm according to claim 1,2 or 3, wherein each said jet is screw-threadedly received in a corresponding orifice in said arm.

5. A distributor arm according to claim 1,2,3 or 4, wherein the support member is a strap of a plastics or synthetic rubber material.

ó. A distributor arm according to claim 5, wherein the strap has a greater width than thickness.

7. A distributor arm according to any of claims 1 to 6, wherein the whole of the support member is flexible but flexure is confined to said flexure region.

8. A distributor arm according to claim 7, wherein flexure is confined to said flexure region by applying a stiff plate over that part of the support member where flexure is not required.

9. A distributor arm according to any of claims 1 to 6, wherein the whole of the support member is relatively inflexible except at its flexure region.

10. A distributor arm according to claim 9, wherein the flexure region is formed by localized thinning of the member locally to increase its flexibility.

11. A distributor arm according to any preceding claim, wherein the plunger is mounted in a body which is attached to an end of the support member.

12. A distributor arm according to claim 11, wherein the body and support member together are a onepiece plastics moulding.

13. A distributor arm according to claim 12, wherein the body portion is moulded around one end of the plunger.

14. A distributor arm for a filtration plant substantially as herein described with reference to Figures 2 and 3 of the accompanying drawings.

15. In or for a distributor arm as claimed in claim 13, a one piece plastics moulding comprising an elongate support member having a body at one end, said body having a plunger projecting therefrom, the body having been moulded around one end of the plunger.

16. A filtration unit which comprises a filter bed and at least one hollow distributor arm as defined in any of claims 1 to 14.

17. A method of biologically treating aqueous effluents wherein there is used a filtration unit as claimed in claim 15.

18. A method according to claim 17, wherein the filter bed is composed of high voltage plastics filter elements, and wherein the aqueous effluent is sewage.