GB2070971A - Air cleaner - Google Patents

Abstract

In an air cleaner employing a plurality of pleated paper filter elements each in the form of a frustrum of a cone mounted in a common tubular casing having a first opening axially thereof communicating with the inside of said elements and a second opening in the cylindrical wall of said casing communicating with the outside of said elements the filter elements are disposed end-to-end so as to exhibit a progressively decreasing diameter lengthwise of the casing. Preferably the axis of the element assembly is tilted relative to the axis of the casing away from the second opening 1, whereby the radial clearance between the filter element and the opening is increased, without increasing the casing size. Opening 1 may be radially or tangentially directed. The casing may be constructed in sections, corresponding in length to the elements, enabling various sizes of air cleaner to be assembled. <IMAGE>

Description

SPECIFICATION Improvements in and relating to air filters This invention relates to air cleaners of the kind comprising a casing having an inlet and an outlet and a pleated paper filter element mounted inside the casing so that in use, air flows from the inlet to the outlet through the element. More specifically, it is concerned with air cleaners in which the filter element is generally tubular in the form of a frustrum of a cone whose open ends are arranged to abut against opposite ends of the casing in sealing relation therewith so that air flowing from inlet to outlet is constrained to pass through the tubular wall of the element.

The filter element itself is usually replaceable, the casing being divisible to permit this replacement which is effected either at regular intervals, or simply whenever the element becomes choked by whatever contaminant is being filtered out of the air. In order to maximise the time between such successive replacements it is very desirable that the wall of the element should present the greatest possible utilisable surface area for receiving the contaminant without unduly obstructing either the inlet or outlet and that the flow of contaminated air should be evenly distributed over this surface area. The first of these requirements may be met in part by making the outside of the element the inlet side for the contaminated air, but for a given casing size, the second requirement restricts the maximum possible diameter of the element.

Unfortunately, the size of the casing is also very often restricted by the space available to house it, a factor which is often outside the control of the cleaner manufacturer, particular in the automotive industry.

Increasing the filter element thickness radially inwardly can yield a valuable increase in the total area of paper, but in the context of a restricted size of casing it may also result in the outlet being at least in part obstructed, so that an excessive pressure drop appears across the element.

In the case of pleated paper, further complications arise. The peaks and troughs of the pleats usually extend axially of the element and the depth of the pleats determines the radial thickness of the element. Clearly, the spacing of the pleats and their depth greatly affects the total utilisable surface area of paper in the filter, but a much more important practical consideration is the ease with which contaminating particles can penetrate into the pleats. Too close a spacing and/or too deep a pleat results in a large surface area but one which is poorly utilized because the walls defining the pleats, especially their radially innermost regions, are too close together.

As one reduces casing diameter (for a given throughput), problems of increased pressure drop and excessive air velocities around the element, coupled with asymmetric dust distribution over the element surface manifest themselves. The increased pressure drop is the most serious problems, particularly where the first opening in the casing is tangentially directed.

According to the present invention, in an air cleaner of the kind set forth above employing a pleated paper filter element in the form of a frustrum of a cone mounted in a tubular casing having a first opening axially thereof communicating with the inside of said element at the relatively wide end of said frustrum and a second opening in the cylindrical wall of said casing communicating with the outside of said element in the vicinity of the relatively narrow end thereof, the filter element comprises at least two separate element portions disposed end-to-end so as to exhibit a progressively decreasing diameter lengthwise of the element relative to a common central axis.Preferably said central axis is tilted relative to the axis of the casing away from the second opening, whereby the radial clearance between the filter element and the opening is increased, without increasing the casing size.

It has been found that this modification results in a reduced pressure drop across the cleaner, better dust distribution over the area of the filter medium and reduced air velocities around the element portions. For given filter element portions and casing size (length/di ammeter) and at a standard throughput the result is an increase in the useful service life (dust holding capacity) of the element. Alternatively, an increased throughput might be achieved for a given service life.

Preferably, the element portion having the smallest diameter has a smaller number of pleats than any other element portion. Where more than two element portions are employed, the number of pleats in each preferably decreases progressively from the portion having the largest diameter to the portion having the smallest diameter. St will be appreciated that the pleats extend axially of the element and that the number of pleats affects not only their spacing, but also their accessibility for dust holding purposes. Too close a spacing and the radially innermost regions of the pleats are too easily occluded, or indeed not accessible to dust particles. The invention permits the selection of the optimum pleat spacing for each element portion and for a given diameter of casing.Furthermore, it makes it possible to greatly increase the amount of pleated paper in a given diameter of casing, simply by making the casing larger in an axial direction. This is frequently more acceptable than an increase in diameter. It also has the added advantage that a multisection casing can be employed in conjunction with standard length element portions to provide a modular cleaner which can be ex tended to significantly increase the dust holding capacity.

The optional, but preferred tilt of the eie- ment axis can be achieved in at least two ways. Firstly, the opposite ends of the filter element may be arranged to lie in parallel planes which are not normal to the axis of the element. Secondly, the casing itself may be configured to receive and locate a normal element in the tilted axis attitude. This would be a preferred embodiment, since it considerably simplifies element production.

Co-pending application No. 8006177 of even date is directed to preferred. optimised features of element aspect ratio and included angle. The present invention may be combined with that of saifi co-pending application and it is particularly advantageous to do so.

The present invention enables a relatively long frustoconical filter element to be built up from a plurality of element portions assembled endto-end. Each of these portions should preferably be of the optimum aspect ratio and included angle, so as to make best use of the total area of paper, without the pleat bunching problems, encountered in relatively long, conventional frustoconical elements. Attention is directed to said co-pendiny application for further exemplitlication of this matter.

The invention will be described by way of example with reference to the accompanying drawings in which Figure 1 is a schematic cross-sectional side view of one form of air cleaner according to the invention, Figure 2 is a schematic cross-section side view of another embodiment of the invention, Figure 3 is a schematic cross-sectional side view of another embodiment of the invention, and Figure 4 is a schematic cross-sectional side view illustrating yet another embodiment of the invention. Since like parts in all of the first three figures correspond, like reference numerals are used as far as is practicable. However, Fig. 4 is numbered differently, to avoid possible misunderstanding.

Referring to Figs. 1, 2, and 3, an air cleaner comprises a cylindrical casing having a radial opening 1 in the cylindrical wall 2 and an axial opening 3 in one end wall 4. The other end is closed by a removable cover 5 which serves to give access to the filter element installed inside the casing. Details of the method of attaching the cover 5 are not material to the present invention and need not be discussed in any detail.

The filter element is constituted by two frustoconical filter element portions (three in Fig. 3) assembled end-to-end to give a progressively decreasing diameter from the axial opening 3. Each filter element portion is constituted by a pleated paper filter medium 7 supported by inner and outer tubes 8, 9 respectively. of perforated metal. The ends of the pleats and the tubes are sealed into end caps 10, 11. The left hand cap (in the figures) is provided with the usual external gasket 12 which prevent leakage around the element.

However, the small diameter end of the right hand element portion is closed by a solid metal plate 13 integral with the end cap 11.

No gasket is needed at this point. The joint (or joints) between the element portions include a metal annulus 14 against which the and caps sealingly abut. The annulus has several radial projections 15 which in conjunction with axial projections 1 6 serve to centre it in the casing, thereby stabilising the joint against misalignment and/or vibration which may be encountered in use. The annulus includes elastomeric facings to seal between the element portions.

Obviousiy, the element portions could be provided with external gaskets, such as gasket 1 S, at each end. The plate 13 is optional in this case.

Referring to Fig. 1 in particular, the two filter element portions are both symmetrical and symmetrically disposed inside the casing.

However, the number of pleats in the paper filter medium in each filter element is selected to optimise the pleat spacing, thereby avoiding the problem of excessively close a pleat spacing at the relatively narrow diameter end and too wide a pleat-spacing at the opposite end, both referred to a single element of length sufficient to occupy the space available.

Fig. 2 shows a modification of the arrangement just described. In it, the axis of the filter element is tilted relative to the axis of the casing away from the opening 1, so that although the filter element is the same as in Fig. 1, there is a significantly increased radial clearance between the opening 1 and the adjacent portion of the element. The degree of tilt necessary for this is achieved by shaping the end wall 4 around the opening 3 and by correspondingly shaping the cover 5, so that the filter element is supported between two parallel planes which are not normal to the axis of the casing, although they are normal to the axis of the element itself. In Fig. 3, this principle is used in a three element portion version of the air cleaner of Fig. 2. Previous comments about optimising the number of pleats in each element portion apply equally to Fig. 3. In this case, the number of pleats will increase stepwise from right to left in the figure, a different number of pleats being optimum for each element, of course. Also, it should be noted that the element is both tilted and supported at each portion-to-portion joint, as described earlier.

Fig. 4 illustrates how the basic principle of the invention can be applied in practice to increase dust holding capacity, without increasing the overall diameter of the casing.

The present invention lends itself to a modular concept in which the casing is built up from an outlet section 20, an inlet section 21 and an end section 22, together with at least one body section 23, so that the casing as a whole accepts a standard length of filter element assembly. Further body sections may be introduced to enable two, three or more element portions of equal length to be used, without altering the other parts of the casing.

Each doubling of the length of the casing has the effect of approximately doubling the dust holding capacity for a given air flow, or throughput.

It should be noted that the first opening in the casing is preferably the inlet to the filter and the axial opening is preferably the outlet, since this configuration results in the best possible utilisation of the area of the paper filter medium. Furthermore, the diameter of the axial opening should be as large as possible, at least as large as the full internal diameter of the abutting element portion.

Likewise, the first opening should be of similar diameter. This results in the lowest possible pressure drop across the cleaner. The first opening may be radially or tangentially directed. In the latter case, the tilted axis feature is especially valuable, because it has been found to largely compensate for the increased pressure drop attributable to the swirl caused by tangential flow inside the casing.

Claims (10)

1. In an air cleaner of kind employing a pleated paper filter element in the form of a frustrum of a cone mounted in a tubular casing having a first opening axially thereof communicating with the inside of said element at the relatively wide end of said frustrum and a second opening in the cylindrical wall of said casing communicating with the outside of said element in the vicinity of the relatively narrow end thereof, the filter element comprises at least two separate element portions disposed end-to-end so as to exhibit a progressively decreasing diameter lengthwise of the element relative to a common central axis.

2. The air cleaner of claim 1 wherein said central axis is tilted relative to the axis of the casing away from the first opening, whereby the radial clearance between the filter element and the opening is increased without increasing the casing size.

3. The air cleaner of claim 1 or claim 2 wherein the number of pleats in each element portion is selected for optimum filter performance of each of said portions.

4. The air cleaner of any one of claims 1 to 3 wherein the casing has a modular configuration, being assembled from a plurality of sections joined to form a casing capable of receiving a preselected number of filter element portions in end-to-end relation.

5. The air cleaner of claim 4 wherein said sections comprise an end section, an inlet section and an outlet section together with at least one body section, whereby the number of body sections is selected to form a casing capable of receiving said preselected number of filter element portions.

6. The air cleaner of any one of claims 1 to 5 wherein the second opening is the inlet to the cleaner.

7. The air cleaner of any one of claims 1 to 6 wherein the second opening is directed generally radially of the casing.

8. The air cleaner of any one of claims 1 to 6, wherein said second opening is directed generally tangentially of the casing.

9. The air cleaner of claim 6, claim 7 or claim 8 wherein the first opening has a diameter substantially equal to the inside diameter of the element portion abutting thereto.

10. An air cleaner substantially as hereinbefore described with reference to and as illustrated by the accompanying drawings.