GB2125313A

GB2125313A - Gas filter and element therefor

Info

Publication number: GB2125313A
Application number: GB08223795A
Authority: GB
Inventors: Francis Couesnon
Original assignee: Knitmesh Ltd
Current assignee: Knitmesh Ltd
Priority date: 1982-08-18
Filing date: 1982-08-18
Publication date: 1984-03-07
Also published as: GB2125313B

Abstract

A gas filter element comprises a plurality of contiguous lengths of a flexible self-supporting medium which comprises metal wire or metal and plastics wires formed into a braided or knitted mesh tubing. As shown the tubing is helically wound round a perforate sleeve 3 to form an annular filter element for an I.C. engine intake, but an alternative flat element comprises a pad made up of separate parallel lengths of tubing. <IMAGE>

Description

SPECIFICATION Gas filter and element therefor This invention relates to a gas filter and to an element therefor.

Gas filters typically comprise a housing having an inlet and an outlet for gas and a filter element in a housing in the path of gas through the device.

The filter element may take a variety of forms. For example, an air filter for a motor car engine may have a paper or non-woven fabric element.

Another type of air filter element is made from plastics foam. Such filter elements generally require replacement from time to time, due for example to blockage of the small pores through the element by entrapped dirt particles. It has also been proposed to use pads of knitted wire mesh as filter elements in air filters and other types of gas filter. Although such wire mesh filter elements are durable, it is difficult to clean them since the mesh must be somewhat tightly packed to obtain the necessary filtration efficiency and it is generally impractical to open out the mesh for cleaning purposes.

There is accordingly a need to provide a gas filter with a durable element that can be dismantled for cleaning and readily reassembled for re-use.

The present invention accordingly seeks to overcome the problems caused by use of knitted mesh filter elements in gas filters and to provide a novel form of gas filter that employs an easily cleanable knitted mesh filter element.

According to one aspect of the present invention there is provided a gas filter element comprising a plurality of contiguous lengths of a flexible self-supporting tubular element comprising wire formed into a knitted or braided mesh.

According to another aspect of the present invention there is provided a gas filter comprising a housing having an inlet and an outlet for gas and a filter element in the housing in the path of the gas, which filter element comprises a plurality of contiguous lengths of a flexible self-supporting tubular element comprising wire formed into a knitted or braided mesh.

Although the filter element may comprise a single layer formed by contiguous lengths of the -tubular element, it will usually be preferred to use a multi-layer construction.

The tubular element is flexible and selfsupporting, that is to say it is formed of a wire that is sufficiently thick for the element normally to retain its tubular form without flattening. However it can be flattened upon application of gentle pressure, as for example by squeezing between the fingers, but reverts to its original shape upon removal of the flattening pressures.

The tubular element may be formed from wire alone, or from a wire together with a lower surface energy filament, for example a plastics filament.

Hence in one embodiment the element comprises side-by-side wire and plastics filaments knitted in tubular form. Conveniently the tubular element is knitted in stocking stitch. However other forms of knitting may be used, if desired, e.g. rib stitch. In such elements the wire is preferably a resilient high tensile metal wire, such as a stainless steel wire, whilst the plastics filament, if present, may be for example a polyethylene or polypropylene filament or the like. Typically the tubular element ranges in diameter from about 5 mm to about 25 mm and can be knitted, for example, from a stainless steel wire of diameter between about 0.12 mm and about 0.3 mm.

The filter element may comprise a pad formed from a plurality of discrete lengths of the tubular element laid side-by-side in contiguous fashion in one or more layers. Alternatively the filter element may comprise a single piece of the tubular element which is folded or coiled to form a singleor multi-layered filter element. However in a particularly preferred form of gas filter element a single continuous piece of the flexible selfsupporting tubular element is wound on to a former, such as a spool, so as to build up a filter element comprising at least one layer on the former consisting of a plurality of contiguous sideby-side turns of the tubular element. Preferably the device includes two or more such layers. In this way an annular body made up of the tubular element wound on the former is built up.The former desirably has a cross section such as to facilitate winding on the tubular element so that the inner turns of the tubular element conform to the outer surface of the former. Hence the former is preferably cylindrical and is conveniently formed with a flange at each end after the manner of a spool. However, other shapes of former are possible, e.g. frusto-conical, barrel-shaped, hourglass-shaped, and the like. Similarly other cross sections than circular are possible, e.g.

hexagonal, elliptical, octagonal, and the like.

Although the tubular element is flexible it cannot be made to conform to a former of too small a diameter. Generally speaking it will be preferable to use a former of a diameter that is at least about 3 times and preferably at least about 4 times the diameter of the tubular element.

In the gas filter element of the invention the contiguous lengths of the tubular element are generally arranged so that, in use, the direction of gas flow through each of the contiguous lengths is transverse to the axis of that length.

The former may be hollow. It may have apertures in its outer surface as, for example, by being made of metal mesh or of expanded metal.

In this way the hollow former may act as the inlet or outlet for gas being filtered; in this event the outlet or inlet, as the case may be, may comprise an end face of the annular body or the radially outer face thereof, or both.

In order that the invention shall be clearly understood and readily carried into effect, a preferred embodiment thereof will now be described, by way of example only, with reference to the accompanying drawings, in which:~ Figure 1 is a side view of a short length of a flexible, resilient tubular element for use in the practice of the invention; Figure 2 is a perspective view of a longer length of the element of Figure 1 after bending into a curved shape; Figure 3 is a perspective view, partly in section, of an air filter incorporating an element of the type of Figures 1 and 2; and Figure 4 is an exploded view of the air filter of Figure 3, showing the coiled element to an enlarged scale compared with the rest of the filter.

Referring to the drawings, Figure 1 shows a short length of a flexible tubular element 1 formed of a resilient high tensile steel wire knitted into tubular form. Typically the diameter of the wire lies in the range of from about 0.12 mm to about 0.3 mm. Tubular element 1 is formed as a weft fabric with 12 wales and has a diameter of about 12 mm. It is both flexible and self-supporting.

Hence it normally retains its tubular shape; it can, however, be flattened by gentle squeezing between the fingers, although it reverts to its tubular shape upon removal of the flattening force due to the inherent resilience of the wire from which it is knitted. Since tubular element 1 is resilient it can be bent to a spiral form, as shown in Figure 2, which it retains after being bent to that shape. Moreover, in view of its knitted construction and the stiffness of the wire from which it is formed, it is extensible in length, without significant change in diameter and without elastic deformation of the wire, from a compressed condition in which the loops of one course abut against the opposed loops of the next but one course to an extended condition in which the loops of all the courses are fully extended.

Depending on the rigidity of the wire and on the loop size of the weft fabric, the tubular element 1 may be extensible by, for example, about one third or more between these two conditions. In addition the tubular element 1 can be stretched elastically somewhat under appropriate tension.

Figures 3 and 4 illustrate an air filter 2 constructed according to the invention. This comprises an inner tubular metal mesh former 3 on which is spirally wound an appropriate length of tubular element 1 so as to form a filter element package which is inserted in an outer body 4 having a cylindrical portion 5 of metal mesh fitted to an end plate 6 which is provided with a threaded hollow spigot 7 by means of which the filter can be mounted on a carburettor. Within body 4 is fitted a threaded annular member 8 supported on legs 9; member 8 enables an end plate 10 to be secured in place by means of a thumbscrew 11.

Since element 1 is resilient it maintains its shape without flattening even when wrapped around the former 3.

If the mesh of element 1 were to be extended into a plane, i.e. cut and laid flat, then the free area would normally be between about 93% and about 99%. In tubular form the free volume of element 1 is about 99.5%.

By winding on an appropriate length of element 1 a plurality of layers of element 1 is built on former 3, each layer consisting of a plurality of contiguous turns of element 1. Preferably one end of element 1 is anchored to former 3 adjacent one of its ends and the element 1 is maintained under sufficient tension during winding to stretch it slightly beyond the afore-mentioned extended condition and temporarily reduce its diameter so that, when the tension is released, possibly after insertion of the package of former 3 and element 1 into the outer body 4, the element 1 reverts elastically to its original length and diameter, thereby ensuring that each turn of element 1 contacts the adjacent turns and no gaps are left between adjacent turns.

As will be apparent from the drawings, in use air is drawn radially inwardly through the annular filter element formed by winding the tubular element 1 onto the former 3, the direction of flow through the tubular element 1 being at all times transverse to the axis of the tubular element 1.

An advantage of the illustrated air filter is that there is a large free volume and the central space in element 1 can act to collect solid particle deposits. Therefore, the filter will have a high solids holdup potential with, in the clean state, a very low pressure drop. As the solid is deposited in the layers of the annular body then the pressure drop will increase. A particularly attractive feature of this construction is that when the element 1 is loaded with solids it can be dismantled by simply turning off the former 3 on to which the element 1 is wound. The element 1 can then either be shaken or steam cleaned or taken through a solvent bath to clean and then re-wound under identical conditions on to the former 3. It therefore has potential for a re-usable filter with a high solids loading capacity and low pressure drop. The construction is such that although the pressure drop is low, the interception efficiency is high, since with respect to solid particles passing through the media the wires are essentially in a random array. Since multi-layers are used, the interception efficiency can be arranged to be almost 1 00 percent. The construction of the illustrated air filter also provides a simple means of controlling the filter depth by varying the length of element 1 wound on to the former 3 and therefore the number of layers in the resultant annular body for filtration.

Claims

1. A gas filter element comprising a plurality of contiguous lengths of a flexible self-supporting tubular element comprising wire formed into a knitted or braided mesh.

2. A gas element according to claim 1, in which the wire is a stainless steel wire.

3. A gas filter element according to any one of claims 1 to 3, in which the wire has a diameter between about 0.12 mm and about 0.3 mm.

4. A gas filter element according to any one of claims 1 to 3, in which the tubular element is knitted from wire.

5. A gas filter element according to any one of claims 1 to 3, in which the tubular element is knitted from wire together with a low surface energy filament.

6. A gas filter element according to any one of claims 5, in which the filament is a polypropylene or polyethylene filament.

7. A gas filter element according to any one of claims 1 to 6, in which the tubular element is knitted in stocking stitch.

8. A gas filter element according to any one of claims 1 to 7, in which the tubular element ranges in diameter from about 5 mm to about 25 mm.

9. A gas filter element according to any one of claims 1 to 8, in which the contiguous lengths are arranged in a plurality of layers.

10. A gas filter element according to any one of claims 1 to 9, in which a single continuous piece of the flexible self-supporting tubular element is wound on a former so as to build up at least one layer on the former consisting of a plurality of side-by-side turns of the tubular element.

1 1. A gas filter element according to claim 10, in which the side-by-side turns are contiguous.

12. A gas filter element according to claim 10 or claim 11, in which the former has a cylindrical surface.

13. A gas filter element according to any one of claims 10 to 12, in which the former is spoolshaped.

14. A gas filter element according to any one of claims 10 to 13, in which the former has a diameter that is at least about 3 times the diameter of the tubular element.

15. A gas filter element according to any one of claims 10 to 14, in which the former is hollow.

16. A gas filter element according to claim 1 5, in which the former has apertures in its outer surface.

17. A gas filter element constructed and arranged substantially as herein described and illustrated in the accompanying drawings.

18. A gas filter comprising a housing having an inlet and an outlet for gas and, in the housing in the path of the gas, a filter element according to any one of claims 1 to 17.

19. A gas filter according to claim 18, in which the contiguous lengths of the filter element are arranged so that, in use, the direction of gas flow through each of the contiguous lengths is transverse to the axis of that length.

20. A gas filter constructed and arranged substantially as herein described and illustrated in the accompanying drawings.