US3633751A

US3633751A - Lamina plate filter

Info

Publication number: US3633751A
Application number: US823057A
Authority: US
Inventors: Ronald John Stevens
Original assignee: Individual
Current assignee: Individual
Priority date: 1969-05-08
Filing date: 1969-05-08
Publication date: 1972-01-11
Anticipated expiration: 1989-01-11

Abstract

Filter elements are provided for use in filtration of fluids, such as petrol, water and air, being made of a pack of laminae with filter gaps designed to facilitate release of entrained material on backflow. Also an associated backflow device is provided which uses a hollow spiral wiping arm to backwash a set of filters sequentially.

Description

United States Patent [56] References Cited UNITED STATES PATENTS 2,959,287 11/1960 Davis et al. 210/222 3,326,374 6/1967 Jones 210/222 X 3,343,676 9/1967 Tyrell 210/108 X 3,346,116 10/1967 Jones 2 l0/222 Primary Examiner- Reuben Friedman Assistant ExaminerT. A. Granger Attorney-Barlow & Barlow ABSTRACT: Filter elements are provided for use in filtration offluids, such as petrol, water and air, being made ofa pack of laminae with filter gaps designed to facilitate release of entrained material on backflow. Also an associated backflow 'device is provided which uses a hollow spiral wiping arm to backwash a set of filters sequentially.

PATENTEDJANI 1 1972 I 3.633.751

SHEET 2 OF 8 I /0 4 5 H i H l 40 f 7 T T Z Inventor RONALD J. STEVENS fllizwfi Attorneys PATENTED JAN? 1 1972 3533751 SHEET 3 [1F 8 Inventor RONALD J. STEVENS PATENTED JAN} 1 m2 3533751 SHEET u [1F a Inventor RONALD J. STEVENS llorney PATENTED JAN] 1 I972 SHEET S [)F 8 Inventor RONALD J. STEVENS fly zatlomeys PATENTEU JAN] 1 1972 3.633751 SHEET 5 OF 8 lnvehlor RONALD J. STEVENS PATENTED JAM 1 I972 3533751 SHEET 7 [1F 8 Inventor RONALD J. STEVENS PATENTED JAN! 1 1972 3,633; 751

SHEET 8 0F 8 Inventor RONALD J. STEVENS LAMINA PLATE FILTER This invention relates to filters for fluids, i.e., gases or liquids, such as water or petrol, air or oxygen.

Known filters from such materials as gauzes, laminae rigid porous media or granules, for example, sand bed filters, all have disadvantages in that it is difficult to create fine, accurate apertures therein and that it is difficult to release the residue retained in the passages of the filtration medium when the filtering action has taken place. This is because the residue becomes mechanically jammed in the filter. For example, if it is desired to retain particles of a cross section of the order of 2 microns, it is necessary that the passages are not materially greater than 2 microns in height. However, for reasons of mechanical strength, the passage must be given a substantial length, for example 1 mm. This means that the ratio of the length of the passage to the cross section thereof is normally about 500. When such a passage is traversed by a particle, it is possible, and in fact almost inevitable, that the particle will become wedged in such a manner that it cannot be removed by backflow, even at very high pressure. Backflow, in fact, normally causes the particle to wedge even more firmly in the passageway. One of the reasons why a particle may wedge is that it is impossible to produce a passage with a length to height ratio of the order of 500 without making slight imperfections in the actual height of the passage. The random and irregular shape of the particles further accents wedging.

Accordingly, one of the objects of the present invention is to provide a filter for fluids which avoids, or at least mitigates, the difficulties and disadvantages hereinbefore described. Furthermore, such a filter should have apertures of extremely accurate dimension and be of extreme fineness as regards height, at the same tim being provided with means by which the greater the buildup of pressure the greater retention of the restrained material. Additionally, the residue retained or wedged in the apertures should be able to be released at an appropriate time by backflow with a minimum loss of backflow fluid.

According to one aspect of the present invention there is provided a filter which comprises a pack of laminae variously perforated so as to provide inflow and outflow passages, and being so constructed that on forward flow a filter gap is formed between part of one lamina and a part of an adjacent lamina spaced therefrom by a predetermined distance, the part of the said one lamina and the part of the adjacent lamina being able to move apart relatively on backflow, thus releasing any residue trapped in the filter gap. The flow passages into and out of the pack of laminae are arranged serially.

The flow passages into the pack of laminae are arranged so as to supply all the parts of the laminae free to move in one direction, the flow passages out of the pack of laminae being arranged so that fluid which has passed through the filter gaps reaches the external surface of the pack via the passages formed through the various laminae to provide outflow lanes or passages.

if neither of the laminae forming a filter gap is inherently flexible, a series of fine slits or perforations should be provided to allow one of them to hinge. Alternatively, in accordance with another aspect of the invention, the mounting of one of the laminae is flexible, to allow the whole effective area of said one lamina to move away from the said adjacent lamina, or

vice versa.

With a view to increasing the filter edge length of the filter, the laminae may be provided with slits or perforations. This is particularly advantageous if the flap or tongue of the filter is so made, since the slits or perforations produce, in effect, further edges in parallel with the leading edge. If, for example, very fine oxides in the micron size range are being filtered and the filter gap under the tongue is 5 microns and the perforations are for example, half a millimeter, the ratio of perforation to particle size is 500:1 and accordingly no particles will lodge in the perforations, all the filtration being effected by the filter gap which can be opened on backflow when the entrapped particles will be released.

A very important feature of the invention is the fact that only a small amount of lift is required to release the entrapped material, which, accordingly can be done very rapidly.

The backflow pressure used can be extremely high and is preferably applied in bursts of pulselike nature. Selected areas of a filter can be selectively cleaned.

Where the inherent pressure in a system is not sufficient to provide positive lifting of the tongues, high-pressure backwashing can be used provided by normal pumping means or an air water piston effect, derived from a column of water above which is air at pressure. On release the limited volume of water moves at high speed and pressure through the filter. When the water has passed through, the air gives a blast effect to clean the gaps. This provides a very efficient backwash system with economy of water on backwash. Of course, if the filter is being used to filter petrol, petrol should be used to backwash the filter.

A filter according to the invention is particularly suited to use subsequent to magnetic filtration for the removal of oxides. This provides positive filtration for the fine residual particles which are difficult to remove due to the nonprecise nature of magnetic filtering systems.

In a preferred embodiment of the invention the tongue member is caused to sit on the sealing member at an acute angle to filter elements generally. This angle may be produced, for example, by electrodeposition or electroforming lines or areas raised, for example, 2.5 to 5 microns on the end of the tongue or on the surface of the sealing member where they contact near the root of the tongue member. Any other area may be treated to provide the same effect on any of the laminae.

The result of the above is a wedge-shaped passage, nominally, for example, 5 microns high rising to, for example, 10 microns at the end of the tongue. This provides a catchment for contaminant in depth as opposed to the normal thin line gap opening. If the surface of the tongue or sealing member has inherent or induced roughness, for example, bumps and lumps 2 microns high this gives the effect of many sinuous passages. The net result is that the bumps function as improved residual particle traps.

lf inlet fluid is allowed over the whole of the upper surface of the tongue member, the side edges of the tongue member, as well as the front edge of the tongue member thus considerably extending the filtering edge by a considerable factor compared with a normal edge filter. Furthermore, if a slit is formed in the tongue member this will also further increase the filtering edge, since then the edges of the slit will also act as filtering edges. Furthermore, a further tongue member could be mounted above the first, the first being provided with a port correlating to the separator passage, with provision for a gap between the two tongues.

According to another aspect of the present invention there is provided a filter, which comprises a pack of laminae variously perforated so as to provide inflow and outflow passages and being so constructed that a filter gap is formed between part of one lamina and a part of an adjacent lamina spaced therefrom by a predetermined distance, the ratio of the overlap or underlap of the laminae at the gap to the gap being small. The ratio will depend to a considerable extent on the size of particle to be entrained and thus on the size of the filter gap. Thus, for a filter gap of, for example, 10 microns, an overlap of 12 /2 micron may be provided. However, for a filter gap of l or 2 microns the overlap is still preferably about 12% microns. On the other hand, an underlap or overlap of 50 microns can be used with advantage with a 75 micron filter gap. With this arrangement, the likelihood of residue being jammed in the filter gap is considerably reduced, since with the prior art constructions the said ratio was normally of the order of 500. Such a construction can, with advantage, be heated to make all the laminae adhere to the adjacent ones.

The laminae used in the present invention may be of any suitable material resistant to corrosion in the fluid to be filtered. Suitable materials are, for example, metals and metal al- Ioys and plastics materials such as P.T.F.E., Nylon or Mylar, formed to the desired shape and configuration by a process such as electroforming, etching, electroplating or any other suitable process, for example, machining. Generally. it is preferred that the laminae be made of brass when petrol is to be filtered, stainless steel or nickel plated iron when water is to be filtered. Of course, two or more different lamina materials could, if desired, be used in the same filter.

The filters of the invention can be used with advantage in the magnetic separation of particular minerals and accordingly the invention further provides a magnetic filter apparatus comprising a filter in accordance with the invention. It should, in particular, be noted that, by the application of alternating current at least one side of the filter laminae can be violently shaken to release and adherent material. This can be done in the presence of backflow or airblast. It will be observed that magnetic filter apparatus according to the invention lends itself to the provision of vast surface areas using a minimum of magnetic material.

In a magnetic filter apparatus according to the invention provided with flapper filter plates, it is sometimes not desirable to lift the tongue by backflow and should alternating current not provide sufficient lift, pneumatic or hydraulic pressure may be supplied to passages in the laminae, or in additional laminae, which passages terminate between the root of the tongue and the space thereunder. A very high pressure may be applied, but very little volume of fluid is required due to the small clearance.

It will be seen that any number of packs of laminae may be used in parallel or in series and these may be used in stationary or rotary systems where through-put and cleaning may take place in predetermined cycles in relation to recovery and rejection of the fractions, flux being applied or removed as desired.

According to a further aspect of the present invention there is provided a filter, which comprises a pack of laminae variously perforated so as to provide inflow and outflow passages, and being so constructed that on forward flow a filter gap is formed between part of one lamina and a part of an adjacent lamina spaced therefrom by a predetermined distance, the part of the said one lamina and the part of the adjacent lamina being able to move relatively apart on back flow, thus releasing any residue trapped in the filter gap, characterized in that one of the two plates comprises a tongue capable of resting at an angle to the other of the two plates. This embodiment of the invention allows for provision of accurately made filter gaps in the micron range from readily available materials such as rolled foils 25 microns thick, at the same time making it still possible to use magnetic flux if desired.

In this embodiment, for each gap or set of gaps is is necessary to use a seal plate, a spacer plate, a tongue plate and a separator plate, arranged one on top of the other, any number of sets being used in a pack of laminae. To assemble such a filter one starts with an end plate or set of end plates so arranged to allow flow into specific areas of the pack and complete with a similar plate or set of plates closing the pack and allowing flow to emerge at specific areas. Next is provided the separator plate, then the tongue plate, the spacer plate and finally the seal plate. To assist the assembly pinholes or locating points should be provided on the laminae, preferably on the border thereof. On pressing the pack of laminae together, at the border there is a consistent thickness where the edge of the tongue is in juxtaposition with the spacer plate if these laminae are the same thickness at the edges. Inside the borders the tongues resting on the spacers will be displaced and lie at an angle, but are free to do this because the border of the separator plate is appropriately shaped. The leading edge of the tongue is preferably provided with teeth, extending back to and beyond the spacer plate. In the seal plate, the slits in communication with the outflow cease at a predetermined point and the tongue which is clamped between the seal plate and the separator plate, is distorted at an angle to the seal plate, thus providing a gap of predetermined dimension. It is clear that such flexible metal will lay as a curve rather than as a straight line. This enhances the vernier effect. This embodiment of filter can also be used, with advantage, with the magnetic filter apparatus.

The present invention also provides filter apparatus having a backflow washing mechanism, which filter apparatus comprises a central tube having a plurality of packs of laminae mounted thereabout, means for feeding fluid to and from the packs of laminae, one of said means being inside and one outside said central tube, said central tube containing a backflow washing mechanism having a hollow spiral wiping arm arranged to cover the flow passages sequentially. Preferably, the central tube and wiping arm of hollow spiral section are constructed from sections, preferably interlocking, enabling the assembly to be of any desired length, and hence capacity, from a limited number of standard parts. Advantageously, the wiping arm, laminae and central tube are mounted flangewise and assembled from one end. The central tube, while being circular inside is advantageously of square outside cross section and may be made of sections of plastics material or metal or metal alloy, molded, die cast or machined to nest or corelate to one another. This arrangement is of great importance when dealing with fluids of explosive nature because the whole structure can be conveniently made as a flameproof structure or electrical circuitry can be isolated from the fluid.

It should be noted that in the magnetic filter system the filter gap can normally be adjusted by altering the flux.

For a better understanding of the present invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:

FIG. 1, shows a section through a pack of laminae forming a filter element in accordance with the invention,

FIG. 2, shows a plan view of an end or blanking off plate of the pack of laminae of FIG. 1 containing the inlets for fluid to be filtered,

FIG. 3, shows a plan view of an intermediate spacer plate of the pack of laminae of FIG. 1,

Flg. 4, shows a plan view of a flapper filter plate of the pack laminae of FIG. 1,

FIG. 5, shows a plan view of a filter gap spacer plate of the pack of laminae of FIG. 1,

FIG. 6, shows a plan view of an intermediate flow plate of the pack of laminae of FIG. 1,

F lg. 7, shows a plan view of a cell spacer plate of the pack of laminae of FIG. 1,

FIG. 8, shows a plan view of an end or blanking off plate of the pack of laminae of FIG. 1, containing outlets for fluid which has been filtered,

FIG. 9, shows a section of a part of the pack of laminae of FiG. 1, on an enlarged scale, along the line IX-IX of FIGS. 2 to 8,

FIG. 10 shows a plan view of the coincidence of the flapper filter plate of FIG. 4 in relation to the gap spacer plate of FIG.

FIG. 11, shows a plan view of the coincidence of the intermediate spacer plate of FIG. 3 in relation to the flapper filter plate of FIG. 4,

FIG. 12 shows a section of part of the pack of laminae of FIG. 9, in the direction XIIXII of FIG. 9,

FIG. 13, shows a section part of the pack of laminae of FIG. 9, in the direction XIIIXIII of FIG. 9,

FIG. 14, shows a view similar to FIG. 9 or part thereof during backwashing of the filter element,

FIG. 15, shows a plan view of a modification of the gap spacer plate of FIG. 6,

FIG. 16, shows a plan view of a modification of the flapper filter plate of FIG. 4,

FIG. 17, shows a sectional view of the coincidence of the gap spacer plate of FIG. 15 and the flapper filter plate of FIG. 16 in a pack of laminae,

FIG. 18, shows a sectional view of a modification of the pack of laminae of FIG. 17, having two flapper filter plates adjacent one another,

FIG. 19, shows a sectional view of a wedge-type of filter element in accordance with the invention, made up of a pack of laminae,

FIG. 20, shows a plane view of a seal plate of the pack of laminae of FIG. 19,

FIG. 21, shows a plan view of an element of a backwash in accordance with the invention,

FIG. 22, shows a cross-sectional view of two elements of FIG. 21 mounted facing the same direction,

FIG. 23, shows a cross-sectional view of two elements of FIG. 21 mounted face to face,

FIG. 24,A, shows a plan view of a segment of a backwash unit,

FIG. 24,8, shows a diagrammatical view, partly in section, of a part of a helix of segments of FIG. 24B of a backwash unit,

FIG. 25, shows a plan view of a modified filter plate according to the invention,

FIG. 26, shows the filter plate of FIG. 25 as for filtration and as for backwashing,

FIG. 27, shows a plan view of a further embodiment of filter element, and

FIG. 28, shows a diagrammatical perspective view of a magnetic self-cleaning filter according to the invention.

Referring now to the drawings, and in particular to FIGS. 1 to 14 thereof, there is shown a filter element according to the invention made up of a pack of laminae. From the top, the pack comprises a stack consisting of an end or blanking off plate 1, an intermediate spacer plate 2, a flapper filter plate 3, a filter gap spacer plate 4, an intermediate flow plate 5, another filter gap spacer plate 4, another flapper filter plate 3 and another spacer plate 2, with a similar stack in reverse order therebelow with a cell spacing plate 6 between the two stacks, the end or blanking off plate 1 at the bottom of the reversed stack being replaced by an end or blanking off plate 7. The plate 1 contains inflow lanes 8 and the plate 7 contains outflow lanes 9.

FIG. 10 shows the coincidence of the flapper filter plate 3 and the filter gap spacer plate 4, demonstrating that the flap edge of plate 3 is supported on wide edge parts 10 of plate 4 and FIG. 11 shows the coincidence of the flapper filter plate 3 and the intermediate spacer plate 2, demonstrating that the root of the flap is gripped by vertical bars 11 of the plate 2.

The laminae of the pack may be of any suitable thickness, except the filter gap spacer plate 4. This plate 4 separates two flapper filter plates form the intermediate flow plate 5 (see FIG. 9) and it is the thickness of plate 4 which provides the gauge of the filter element. If the thickness of one thousandth of an inch thick is used, a gap of slit of this thickness will be formed along the length l2l2 of FIG. 12.

The length of the passage towards the outflow lane 9 via the underside of the plate 3 is governed by the width of the bars 13 of the plate 5.

In use of the filter element shown in FIGS. 1 to 14, fluid to be filtered enters the inflow lanes 8 and passes through the slit provided by the thickness of the plate 4 under the tongue or flap 14 of the plate 3 and to the outflow lane 9. The residue removed from the fluid by the filtering action will collect on the frontal edges of the filtering gaps and some particles will stick or become wedged in the passages defined by the width of the bars 13 of the plates 5. Thus, to any intrinsic pressure drop across the filter element due to the fine passages therethrough will be added a pressure drop due to buildup of residue in the passages, restricting flow therethrough. A very important result of this is that the pressure holding the plates 3 against the plates 4 will rise and the flaps or tongues 14 will be caused to bear down with increased pressure. As the area of the flaps or tongues 14 may be very large as compared with the area of the flow passages, almost all the total pressure differential will be exerted in holding the tongues or flaps 14 in position.

Arising from this important feature of the invention is the corollary that on reverse flow or backwashing, the flaps or tongues 14 will have the pressure exerted thereon reversed compared with that during forward flow. In consequence, the

unit

flaps or tongues 14 of plates 3 will lift away from their resting point on the plates 4 and any residue trapped in the filtering passages will be released and be free to flow away as shown diagrammatically in Flg. 14.

It will be appreciated that, in many filter systems the pressure internally of the casing around the elements is or may be very high as compared with atmospheric pressure or the pressure of any other part of the system. In consequence, the scouring action due to the high velocity of flow will clean the filter elements very effectively, with small loss of backflow fluid.

It will be observed that the flaps or tongues 14 are free to move, since the areas of the plates 2 are so arranged that they will not obstruct the same. Thus, the flaps or tongues 14 may rise as far as the limits of the thickness of plates 2 until they reach the next plates, as shown in FIGS. 9 and 14 when the next plates would be plates 5 during filtration and

plates

1, 6 and 7 during backwashing.

The filter gap previously described could be, for example, one-thousandth of an inch high and 1 inch wide. Accordingly, in such a case many flaps or tongues would be necessary to obtain any reasonable amount of storage for residue removed from the fluid to be filtered.

The length of the filter edge or gap is desirably as long as possible in any filter media and in the present case the abovedescribed filter element can be modified to increase said length. The flaps or tongues 14 of the plates 3 can be modified by being castellated or perforated or preferably patterned as shown at 3' in FIG. 16. The intermediate flow plates 5 used in conjunction with a flapper filter plate 3' as shown in FIG. 16 are modified to have slots running across the same, as shown in FIG. 15, so that the fluid may pass through the thickness of the flaps or tongues. FIG. 17 shows how the patterned plates shown in FIGS. 15 and 16 coincide. The pattern used may be of any sort or variety which reproduces the effect of extending the edges of the flaps or tongues.

For very small gaps, the plate 4 may be eliminated and areas of the surface of the flapper plates may be of increased height for example discrete dots or raised portions may be electrodeposited thereon to produce the desired gap. Of course, such raised portions could be provided on the plates adjacent the flapper filter plates instead. Any thickness of electroplating could be used, but this method is particularly useful when gaps of the order of l to 10 microns are required.

It will be observed that any arrangement of plates producing the desired effect may be used so long as the appropriate perforations are provided.

In the filter elements described with reference to FIGS. l5, l6 and 17 of the drawings, the flapper filter plates are, in effect, used singly. However, two or more flapper filter plates may be used adjacent one another. An example of such a filter element is shown in FIG. 18. In this case, the outermost flapper filter plates 3" are of the same pattern as plates 5 of FIG. 15, the flapper filter plates 3 being as shown in FIG. 16. This arrangement provides a prefilter, a very valuable feature in some applications. For example, if the distance between

plates

3 and 3 is 10 microns, particles of this diameter will be retained in this portion together with the finer particles due to the sand-bed effect. The finer particles which pass through will then be retained between plates 3' and 5' and this may be as little as 2 microns or even less. This type of filter element ensures that larger particles, which can waste the very valuable edge length ifthey are not removed. The cleaning effect on baekwashing is not affected and the closing action on forward flow is normally either as effective as hereinbefore described or even more effective.

Filtration in depth is in some cases a necessity or a highly desirably feature, especially when fine particles must be retained with accuracy, in a self-cleaning automatic backwash system. In such cases, a wedge filter according to the invention may be used, successfully down to a filter gap of 1 micron or even less, with ease of production and reasonable economy. An embodiment of such a type of filter element is shown in FIG. 19, in which two flapper filter plates are arranged on each side of a seal plate 16 (shown in FIG. The flapper filter plates 15 are kept away from the seal plate 16 by either electrodeposition in discrete areas 17 or by the interposition of suitable plates. The height of the areas 17 or plates may, for example, be 12.5 microns (0.0005 inches). In this case, at line 18 there will be a gap of nil, rising to I microns at line 19. The gap between

lines

18 and 19 will, accordingly, be wedge shaped. At the line 20 the height of the gap will be 4 microns. Hence, as particles enter at the front edge, those of 12.5 micron size will be restrained, and in depth towards the slots there will be a progressively decreasing size restrained. Some of the fluid will pass directly to the slots 21, but much will follow the easier course to the slots 22 and, according to the position of the forward end of the slot 22, the maximum size particle allowed through can be chosen, for example, 8 micron with the sizes referred to above. However, there is a passage between slots 21 and 22 where they coincide, but this is never greater than 4 microns at one end and 0 at the other.

The effect of the overlap of the slots 21 and 22 is the same as the extended edge and this may be of considerable length as the fluid can proceed in two directions from the slot 22 to the slot 21 and hence the edge length is doubled.

Thus, if the measurements are chosen appropriately, an accurate filter gap even of the order of 1 micron can be created by the type of vernier effect of the slope or curve of the flap or tongue as it is caused to bear down on the seal plate 16. This feature is of considerable importance, since the wedge effect gives great area of filtration and consequent volume for storage or holding capacity for residue and is filtrated in depth without the normal disadvantages that the residue cannot be easily removed or released. Also, filtration to this order of particle size is normally very difficult to achieve by other means, due to the problems which occur in making materials of consistent pore size.

Turning now to another aspect of the present invention, the preferred embodiment of backwash unit according to the invention is shown in FIGS. 21, 22, 23, 24A and 243. As is well known, no system of filtration is truly complete without a backwash (or reverse flow) unit and the unit according to the invention is particularly adapted for use with filter elements according to the invention and in fact, such filter elements are preferably directly mounted on unit. It is also desirable that the backwash unit should be capable of sweeping the filter elements section by section and in as many steps as possible.

The unit comprises a central box having a substantially circular bore therethrough and being externally of square cross section. If desired, the external shape could be altered, so long as there are flat surfaces on which to mount filter elements 26. The central box is made up of sections, for example, half an inch thick, mounted on rods and clamped together. A plan view of a preferred section is shown in FIG. 21, and in FIGS. 22 and 23 are shown cross sectional views of two sections of FIG 21, side by side and face to face respectively.

The section shown has a circular aperture centrally thereof and is basically of square cross section. A base plate 23 has mounted thereon corner members 24 both having holes 25 therethrough to enable a stack of elements to be clamped together. Between each pair of corner members a port 27 is formed so that filter elements 26 can communicate with the central aperture of the section.

The sections may be made by any convenient mean but are preferably made by injection molding of a plastics material diecasting or other repetitive process. The section shown was made by diecasting of brass.

In the central aperture of a stack of sections, there are provided segments 28 as shown in FIGS. 24A and 248. Each segment 28 comprises a channel member opening inwardly into through-holes 29 around a collar forming a mounting for a rod 31. The top and bottom faces of the segment is such that it will mate with a similar segment inverted thereon and key with registers on other segments 28. On mounting a number of mated pairs on a rod, preferably helically as shown in FIG.

24B, a flow path if formed by the holes 29 so that fluid fed to the end hole 29 will be distributed to all the channels formed by the mating channel members 30.

When such a helical arrangement is placed in the stack of elements, it will be appreciated that by rotating the segments, it is possible to backwash filters part by part in as many steps as required.

The segments 28 are preferably made by injection molding of plastics material or die-cast, without machining.

The usual associated means are, of course, used with the backwash unit described above.

Using the above techniques it is possible to make units for varying duties and of varying capacities. This is particularly important, since frequently such units will have to be made to fit existing apparatus. Furthermore, the depth of the apparatus can be readily varied.

FIGS. 25 and 26 show part of a modified filter plate in accordance with the invention. A filter pattern 32 is provided in a tongue member or inner frame 35, the tongue member or inner frame 35 mounted via members 33 to an outer frame 34. The seal plate used in conjunction with such a filter plate is similar except that the filter bars of the pattern 32 are displaced and the edges are solid. It is the gap between the edges of the bars of the filter plate and the edges of the bars of the seal plate which provides the filtering action. Since the bars can be of quite narrow thickness, the likelihood of particles smaller than the gap sticking between the bars is slight. The filter plate and seal plate may be separated by an electrodeposit or by an intermediate plate, but, however they are separated, no gap is to be left on filtering between the tongue member or inner frame 35 and the seal plate. On backfiow, the filter plate is forced away from the seal plate, the filter gap is opened and cleaning is quick and simple. This type of construction is very strong and stiff.

FIG. 27 shows a plan view of a further embodiment of filter element in accordance with the invention, known as a consolidated form of element and comprising combe members and split combe members. The filter element is made by etching, when attached to a backing sheet, to which it is shown attached. On removal from the sheet the completely isolated parts will fall away, leaving holes in the element to form flow lanes. The filter elements operate in a manner similar to that described in connection with the filter element of FIGS. 29 and 20.

The present invention also relates to magnetic filtration, that is when the filtration is assisted by magnetic forces. FIG. 28 diagrammatically shows a magnetic self-cleaning filter according to the invention, partly in section. A steel box 36, nickel plated, has mounted in the bottom there of an electromagnetic coil 37 with a core 38 and a filtration unit is mounted in the top thereof between two steel plates 39, which have ports therein to allow escape of filtered fluid.

On passing current through the coil, the filter plates (made of steel, nickel plated) are subjected to a very strong magnetic flux transversely thereof. This is transversely of the fluid flow through the filter gaps thereby considerably assisting the filtering action of the filter. Alternatively, the filter plates could be made of a magnetic nickel alloy.

What is claimed is:

1. A filter comprising a pack of laminae, means forming inflow and outflow passages in said pack, filtering passage means connecting said inflow and outflow passage means, said filtering passage means comprising perforations in said individual lamina with said lamina stacked together having said perforations aligned in predetermined positions to form flow passages, a first specific lamina having a tongue member, filter gap means juxtaposed one surface of said tongue member, said tongue member being hinged on said first specific lamina whereby it moves toward and into said filter gap means during backflow of a fluid through the filter thus releasing any residue trapped by said tongue member during the forward flow of fluid through the flow passages of said filter, a second specific lamina juxtaposed said first specific lamina but on the surface opposite said filter gap means, said second specific lamina having a perforation positioned beneath said tongue member to form a part of said filtering passage means with said second specific lamina having means to prevent said tongue member from moving into said perforation in said second specific lamina during forward flow of fluid through the flow passages of said filter.

2. The filter of claim 1 in which the inflow and outflow passages through the individual lamina forming the pack are arranged serially.

3. The filter of claim 1 in which said first specific lamina having the tongue member is integrally formed from a material having physical properties which make said tongue flexibly deformable away from the plane of the lamina during the backflow operation.

4. The filter of claim 1 in which said tongue has a series of fine orifices formed therein whereby said tongue may hinge along the line of orifices.

5. The filter of claim I wherein the tip of the tongue member is provided with slits which provide additional surface area against which particles to be filtered may be trapped.

6. The filter of claim 1 wherein said second specific lamina has means rising above the plane of its surface upon which said tongue member rests thus causing said tongue to be an gularly positioned with respect to the plane of the laminae generally thus forming a wedge filter for trapping particles therein.

Claims

5. The filter of claim 1 wherein the tip of the tongue member is provided with slits which provide additional surface area against which particles to be filtereD may be trapped.

6. The filter of claim 1 wherein said second specific lamina has means rising above the plane of its surface upon which said tongue member rests thus causing said tongue to be angularly positioned with respect to the plane of the laminae generally thus forming a wedge filter for trapping particles therein.