GB2070970A - Air cleaner - Google Patents

Abstract

In an air cleaner comprising a cylindrical casing containing two substantially identical pleated paper filter elements 7, each in the form of a frustrum of a cone and assembled with their narrow diameter ends in abutting and substantially airtight relation adjacent a first opening 1 in the cylindrical wall of the casing and with their relatively wide diameter ends in abutting and sealing relation to the opposed ends of the casing, at least one of said ends having an opening 3, 3A therein communicating with the inside of the element abutting said end, the axis of each of said element portions is tilted relative to the axis of the casing away from the first opening, whereby the radial clearance between the elements and said first opening is increased without increasing the size of the casing. Inlet opening 1 may be radially or tangentially directed. <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 opposite 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, giving an excessive pressure drop across the element, even before it is used.

in the case of pleated paper, further complications arise. The peaks and troughs of the pleats usually extend axially of the element and then 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 cleaner 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 problem, particularly where the first opening in the casing is tangentially directed.

According to the present invention, in an air cleaner comprising a tubular casing containing two substantially identical pleated paper filter element portions, each in the form of a frustrum of a cone and assembled with their relatively narrow diameter ends in abutting, aligned and substantially airtight relation adjacent a first opening in the cylindrical wall of the casing and with their relatively wide diameter ends in abutting and sealing relation to the opposed ends of the casing, at least one of said ends having an opening therein communicating with the inside of the element portion abutting said end, the axis of each of said element portions is tilted relative to the axis of the casing away from the first opening, whereby the radial clearance between the element portions and said first opening is increased without increasing the size of the casing.

Preferably the first opening is used as the inlet to the air cleaner, the outlet being the other opening, in the end of the casing.

Preferably, two such outlets are provided, one in each end of the casing. This arrangement of inlet and outlet(s) results in better utilisation of the total area of pleated paper making up the element, since the outer surface of the latter is more accessible to dust, particularly as regards the bottoms of the pleats.

It has been found that tilting the axes of the element portions results in a significantly reduced pressure drop across the filter element; it also gives better (more uniform) distribution of dust over the total area of the filter paper, together with reduced air velocities around the element. This latter effect is very important if the first opening (the inlet) is tangentially directed, because the swirl due to a tangentially directed airflow is not converted to static pressure across the element.

It is dissipated progressively around the element and results in a cleaner with a tangential, as opposed to a radial inlet exhibiting a pressure drop penalty of up to 20%, typically about 22cm water gauge. Tilting the element portion axes reduces the flow around them by causing a flow stalling effect such that the pressure drop penalty is significantly reduced. This is valuable where a tangential inlet is needed to mate with the pipework of the associated air intake duct.

Regardless of the inlet disposition, the overall result of applying the invention is that for a given casing and element portions at a standard volume throughput, the result is an increase in the useful service life of the element. This is significant where physical constraints prevent the use of a larger diameter of casing and a larger element, or elements. In the alternative, a rather larger throughput can be achieved for the same element service life.

The present invention may be combined with that of copending application No.

80061 77 of even date relating to element aspect ratio and included angle. Indeed it is preferred that it should be, since the combination yields better performance than either invention on its own.

Referring to the present invention, the desired tilt of the element portion axes can be achieved in at least two ways. Firstly, the opposite ends of the element portions may be arranged to lie in parallel planes which are not normal to the axis of the casing. Secondly, and this is preferred on the ground of simplicity, the ends of the casing may be configured to receive and locate a pair of normal. regular element portions in a tilted axis attitude.

It will be appreciated that in accordance with the teaching of patent No. 1507824, the diameter of the, or each opening in the end or ends of the filter casing should be as large as possible, up to the full internal diameter of the element portion abutting thereto. Likewise, the diameter of the opening in the cylindrical wall should be at least as large as that of the end opening. When two such openings are used, the diameter of the cylindrical wall opening should be greater than that of either of them.

In order that the invention be better understood two embodiments of it will now be described by way of example with reference to the accompanying drawing in which:~ Figure 1 a schematic cross-sectional side view of an air cleaner according to the invention and Figure 2 is a schematic cross-sectional side view of another, preferred air cleaner according to the invention.

Since like parts in both figures correspond, like reference numerals will be used as far as practicable. Referring to the figures, an air cleaner comprises a 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 two filter element portions installed inside the casing. In this particular instance, the cover 5 also has an axial opening 3A. 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 portions are identical and each 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 1 O, 11. These are provided with the usual external gaskets 13 which abut against the end wallicover and prevent leakage between the inside and outside of the element (other than through the filter medium). At the junction between the two element portions a locating washer 12 is provided. This includes a fiat annulus part against which the gaskets abut. It also includes a number of axial 14 and radial projections 15 which engage the insides of the element portions and the cylindrical wall of the casing, respectively. These locate the element portions and centre the annulus respectively.The use of the locating washer and projections helps to improve the stability of the element-to-element joint under conditions of vibration, as would be encountered in an automotive application. The narrow diameter ends may be closed by blanking plates integral with the end caps, or they may be open.

In the latter case the locating washer must also co-operate with annular gaskets similar to 13 and on the end caps 11, in order to prevent leakage between the element portions.

In the following description, only one filter element portion is referred to, for convenience. However, both portions are identical and the description should be read as apply ing equally to both of them.

Referring to Fig. 1, each filter element is a frustrum of a cone but its ends lie in parallel planes which are slightly inclined with respect to a normal to the axis of the cone. Each element is installed in the casing so that one side of it lies substantially parallel to the wall of the casing opposite the radial opening 1.

This causes the axis of the element to be tilted slightly with respect to the axis of the casing and the radial clearance between the opening 1 and the filter element outer perforated metal support tube 9 is thereby increased.

Referring now to Fig. 2, this shows two frusto-conical filter element portions installed in a casing in which the end wall 4 and the cover 5 are themselves arranged in parallel planes which are at a small angle to the normal to the casing axis. The effect is exactly the same as in Fig. 1, but each filter element portion itself is conventional, i.e. symmetrical, with its ends lying in planes substantially normal to the axis of the element. This arrangement has the advantage that only the casing has to be altered, whereas the Fig. 1 cleaner requires a special element, which must be correctly installed. The Fig. 2 ele ment portions will be installed automatically in the correct attitude, without the possibility of operator error, although it will be necessary to use care in re-fitting the cover 5. The latter may be keyed to the casing so as to ensure correct fitting.

The first opening in the casing is preferably the inlet to the filter and the axial openings are preferably the outlets, since this configuration results in the best possible utilisation of the area of the filter medium, as previously explained.

To illustrate the performance of the cleaner of Fig. 2, it was compared with an otherwise identical cleaner in which the element portion axes were not tilted relative to the axis of the casing. The following were the approximate dimensions adopted:~ Casing length 95cm Inlet diameter 18 cm Casing diameter 22cm Outlet(s) diameter 1 3cm Element portion length 46cm (each) No. of pleats 160; pleat depth 3.8cm Throughput 34 cubic metres/minute The element portions were 21cm in diameter at their wide ends and 1 scum in diameter at their narrow ends. At the rated throughput, the conventional, non-tilted axis cleaner had a pressure drop of about 1 3cm of water. The cleaner of Fig. 2 however had a pressure drop of only 8cm of water. This was a significant reduction, for a minor change in construction.

Claims (7)

1. In an air cleaner comprising a tubular casing containing two substantially identical pleated paper filter element portions, each in the form of a frustrum of a cone and assembled with their relatively narrow diameter ends in abutting, aligned and substantially airtight relation adjacent a first opening in the cylindrical wall of the casing and with their relatively wide diameter ends in abutting and sealing relation to the opposed ends of the casing, at least one of said ends having an opening therein communicating with the inside of the element abutting said end, the modification wherein the axis of each of said element portions is tilted relative to the axis of the casing away from the first opening, whereby the radial clearance between the element portions and said first opening is increased without increasing the size of the casing.

2. The cleaner of claim 1 wherein the first opening is the inlet to the cleaner and has a diameter at least equal to that of the opening in one end of the casing.

3. The cleaner of claim 1 or claim 2, wherein openings are provided in both ends of the filter casing and the first opening has a diameter greater than that of either of said openings.

4. The cleaner of any one of claims 1, 2 and 3 wherein the opening in the end of the filter casing has a diameter at least equal to the inside diameter of the element portion abutting thereto.

5. The cleaner of any one of claims 1 to 4 wherein the first opening in the casing is generally tangentially directed.

6. The cleaner of any one of claims 1 to 4 wherein the first opening in the casing is generally radially directed.

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