GB2154894A - Filter element - Google Patents

Abstract

An annular inward-flow filter element for dry-cleaning fluid comprises an outer pleated filter sheet 1, with by-pass holes 7 in the inner folds of the sheet, and an inner filter sheet 2, with a dirt-holding cavity 5 between them which may contain a bed of active carbon 6. When sheet 1 is generally clogged by solids, fluid can still flow through holes 7 to be filtered by bed 6 and sheet 2. In Fig. 4 not shown both sheets are pleated and the bed is omitted. <IMAGE>

Description

SPECIFICATION Filter element In a dry cleaning process a solvent is used to clean articles, such as clothes. The solvent removes and carries away dirt particles and unwanted chemicals from the articles, and, if the solvent is to be reused, it must first have these particles and chemicals removed. This is achieved by using a filter.

Known filter elements have a first annular membrane of filter material, usually a pleated paper cylinder, and inside and spaced from this membrane a second annular membrane of filter material, such as Rayon or Bonded Fibre Fabric. In the case where the first membrane is a pleated paper cylinder, the second membrane may be attached to the inner ridges of the pleats. End caps are used to seal the cavities formed between the first and second membranes, and these cavities may be filled with a granular compound, such as activated carbon granules. A perforated metal tube may be fitted adjacent the first and/or second membranes in order to strengthen the filter element.

The filter element is mounted in a housing which makes the solvent flow radially inward through the first membrane, the cavity, and then the second membrane. The first surface removes dirt particles, colloids and very fine particles such as diatomaceous earth, the last two often being present in the solvent in addition to the dirt particles. The granular compound removes by adsorption and absorption the unwanted chemicals from the dirty solvent. If even very small quantities (less than 1% by volume) of liquid additives have been added to the solvent, the pores of the first filter membrane are very likely to be further clogged up by the additives. These additives are used, for example, to give retexturing qualities, and their use is not uncommon.

For all of the above reasons, the substances removed from the dirty solvent and accumulated on the first membrane resist the flow of solvent. This deposit results in the pressure drop across the filter element increasing. In the dry cleaning industry this pressure drop is measured and used as an indication of the performance of the filter element, and it is customary to consider that the element has reached the end of its useful life when the pressure drop has built up to a pre-determined value. Upon removing the used element, it is nearly always found that it is the first membrane which is clogged up with dirt and that the cavities and second membrane are largely free of filtered residue.This means that the dirt-removing capacity of the cavities and second membrane is being wasted because all fluid must previously have passed through the first membrane which will have removed the dirt. What is needed is some way of bypassing the first membrane when it has become clogged up with dirt so that the second membrane and granules in the cavity, if provided, may continue the dirt-removing function.

Previously, for example in GB-A-1133858, slits have been provided in the second membrane. However, by being in the second membrane, the slits do not provide a way of bypassing a clogged up first membrane. GB A-1209085 discloses a filter with a perforated first membrane. The second membrane is adjacent to and in contact with the first membrane, and this means that the perforations of the first membrane are blind holes which terminate on the second membrane. Since there is no cavity between the two membranes, each hole only affords access to a similar sized portion of the second membrane and there is only one route to each piece of the exposed second membrane. Consequently, should a route become blocked by dirt particles, the respective piece of exposed second membrane is no longer available for filtration.

I have appreciated that by putting perforations such as slits or holes in the first membrane of a known filter element as well as providing a cavity between the first and second membranes, the above problems may be overcome. The provision of a cavity ensures that there are many routes via many perforations to any piece of exposed second membrane. Consequently, should any perforation become blocked by a large piece of dirt, the multiple route redundancy ensures that no piece of exposed second membrane is prevented from filtering out dirt particles.

Therefore, a filter element, according to the present invention, for use in the dry cleaning industry, comprises a first annular perforated filter membrane and a second annular filter membrane which is spaced radially inward from the first membrane to provide a cavity therebetween.

If the second filter membrane is a pleated paper cylinder similar to that of the first filter membrane, the additional surface area of this second filter membrane, compared to that of smooth cylinders used in known elements, ensures that the second filter membrane is able to remove even more dirt particles before it becomes clogged.

Preferably, the cavity, instead of being a void, contains a granular compound which, apart from absorbing and adsorbing the unwanted chemicals, also acts as a filter bed which filters out the dirt by trapping the dirt between the granules. This filter bed may be of substantially uniform consistency, e.g.

made throughout of granules of a similar size, or it may be a multi-part bed in which the parts are radially stacked on one another and are of different consistencies to one another, e.g. in a two-part bed the radially outer part may be made of relatively larger granules which only trap the relatively larger dirt particles and the radially inner part may be made of relatively smaller granules which trap the relatively smaller dirt particles that have passed through without being trapped by the radially outer part of the bed. I have found that the latter filter bed construction, i.e. the multi-part bed, is even more effective than the former construction, i.e. a bed of substantially uniform consistency.

Furthermore, I have also found that, in a two-part filter bed, it is desirable to have the radially outer part made of relatively larger granules of activated clay and the radially inner part made of relatively smaller granules of activated carbon.

A filter according to the present invention, utilizes the whole of the first filter membrane, second filter membrane and filter bed of granules (if provided) for dirt removal, and, therefore, the element has a longer life than elements not incorporating the present invention.

Examples of elements in accordance with the present invention will now be described with reference to the accompanying drawings, in which: Figure 1 is an axial section of a first example of the filter element; Figure 2 is an enlarged view of zone "A" of Figure 1; Figure 3 is a section taken on the line X-X in Figure 2; and, Figure 4 is an axial section of a second example of the filter element.

The filter element shown in Figure 1 has a pleated paper cylinder 1 as a first filter membrane and a cylindrical second filter membrane 2, made of Bonded Fibre Fabric, which is fixed on the outside of a perforated metal support tube 3. End caps 4 seal the cavity 5 formed between the paper cylinder 1 and second filter membrane 2. A filter bed 6 (partially shown) fills the whole of the cavity 5. This filter bed 6 is of two-part construction with a radially outer annular part 6a of relatively larger granules of activated clay surrounding a radially inner annular part 6b of relatively smaller granules of activated carbon, Holes 7 (see Figures 2 and 3) are provided along the length of radially inward pleat ridges of the paper cylinder 1.

Assuming that the element is mounted in a standard housing which causes the fluid to flow radially inward, the fluid will initially flow through the pleated paper cylinder 1, through the filter bed 6 and then through the second filter membrane 2, with most of the dirt being removed by the pleated paper cylinder 1. A small fraction of the fluid passes through the holes 7, through the filter bed 6 and then through the second filter membrane 2, with the dirt being removed by the filter bed 6 and the second filter membrane 2. As the pleated paper cylinder 1 becomes more and more clogged up, a larger fraction of the fluid flows along the second route, i.e. through the holes 7.When flowing along this second route, the fluid initially passes through the outer part 6a of the filter bed 6 and the relatively larger dirt particles become trapped therein and removed, then the fluid passes through the inner part 6b of the filter bed 6 and the second filter membrane 2 and the relatively smaller dirt particles become trapped in both the inner part 6b and the membrane 2.

The existence of the cavity 5 and holes 7 ensures that there are both many fluid routes 8 available which use the same hole 7 before passing through the second filter membrane 2, and many fluid routes 9 available which use different holes 7 before passing through the same piece of second filter membrane 2.

This multiple fluid route redundancy ensures that substantially all the second filter membrane 2 may be used to remove dirt particles before it becomes clogged. Only then will the pressure across the filter element as a whole rise sufficiently for it to need replacing.

The second example of the filter element (see Figure 4) has parts in common with the first example, and these common parts have been given common reference numerals. The second example differs from the first in the following respects.

The pleated paper cylinder 1 is supported by a perforated metal tube 10 as there is no granular compound in the cavity 5.

Instead of the second filter membrane being a smooth cylinder, it is a pleated paper cylinder 11. This further increases the dirt particle removing capacity of the filter element, and this capacity could be increased still further by providing a filter bed in the cavity 5.

In both examples the holes 7 are made big enough to minimize the probability of being bridged and clogged by the same dirt particles that eventually clog up the two filter surfaces.

The holes must not be made too big as otherwise the second filter membrane will clog up, so preventing further functioning of the element as a whole, before the first filter membrane is fully clogged up. This would waste some of the dirt removing capacity of the filter element. Although the perforations have been holes in these two examples, they could equally well have been slits conveniently provided, for example, along the length of radially inward pleat ridges of the paper cylinder 1.

Claims (13)

1. A filter element, for use in the dry cleaning industry, comprises a first annular perforated filter membrane and a second annular filter membrane which is spaced radially inward from the first membrane to provide a cavity therebetween.

2. A filter element according to claim 1, wherein the cavity contains a filter bed of a granular compound.

3. A filter element according to claim 2, wherein the filter bed comprises a radially outer part of relatively larger granules adjacent to a radially inner part of relatively smaller granules.

4. A filter element according to claim 3, wherein the radially inner and outer parts are annular.

5. A filter element according to claim 4, wherein the radially inner and outer annular parts are cylindrical.

6. A filter element according to any one of claims 3 to 5, wherein the relatively larger granules are made of activated clay and the relatively smaller granules are made of activated carbon.

7. A filter element according to any one of the preceding claims, wherein the first filter membrane is a pleated paper cylinder, and the perforations are provided on a radially inward pleat ridge of the paper cylinder.

8. A filter element according to to any one of the preceding claims, wherein the second filter membrane is fixed to the outside of a perforated metal tube.

9. A filter element according to any one of the preceding claims, wherein the second filter membrane is a pleated paper cylinder.

10. A filter element according to any one of the preceding claims, wherein the first filter membrane is fixed to the outside of a perforated metal tube.

11. A filter element according to any one of the preceding claims, wherein the perforations are holes.

12. A filter element according to any one of the preceding claims, wherein the perforations are slits.

13. A filter element substantially as described with reference to the accompanying drawings.