Patent Application
20090020472
The present disclosure relates to a pleated filter. More particularly, the disclosure relates to concentric filter elements.
Traditional cylindrical pleated filters comprise a number of interconnected rectangular panels with short sides extending radially with respect to the axis of the filter element, and long sides extending axially between the ends of the filter element. The maximum number of pleats in a traditional cylindrical pleated filter is determined by the inner circumference of the filter divided by the thickness of the pleats.
Improvements on the traditional radial pleated filter are disclosed in U.S. Pat. No. 2,627,350 (1953) and more recently in U.S. Pat. No. 6,315,130 (2001). The improved configurations provided a design wherein more filtering media can be folded into the same size housing as compared to the traditional cylindrical pleated filters. The term filter media is used herein to generally refer to the materials that can be used for filtering. The filter media can also include materials that primarily provided structural rigidity/support for the filtering material and provide flow channels into and out of the pleat.
Another pleated filtering configuration includes concentrically arranged cylindrical pleated filters elements. An example of a concentrically arranged pleated filter is disclosed in U.S. Pat. No. 5,232,595 to Meyer. One limitation associated with the concentric pleated filter configuration relates to the geometric constraints associated with the cylindrical pleated elements used to construct the concentrically arranged filters.
The present disclosure provides novel concentric filter elements that have advantages over traditional concentrically arranged filters and filters comprising a single cylindrical filter element.
The present disclosure provides a cylindrical filter arrangement and a method of manufacturing a multi element filter. In one embodiment of the filter, the filter includes concentrically arranged cylindrical pleated filter elements, wherein one of the filter elements comprises a plurality of outwardly extending primary pleats positioned between shorter inwardly extending secondary pleats. In one embodiment of the manufacturing method, the method includes configuring concentrically arranged inner and outer filter elements such that their estimated effective lives are about the same for the type of fluid to be filtered.
While the above-identified figures set forth several exemplary embodiments of the disclosure, other embodiments are also contemplated. The figures are not drawn to scale.
It should be appreciated that many alternative geometric configurations and arrangements are also possible. For example, in an alternative embodiment there could be more than two filter elements (e.g., three, four, five, etc.), one or more of the elements may be non-cylindrical (e.g., elliptical), the inner element could have a solid end profile rather than an annular end profile, and other structures may be incorporated within or around the filter elements. It should also be appreciated that the fluid could be configured to flow in the opposite direction as shown. In such an embodiment the inner filter element 14 could act as a pre-filter and the outer filter element 12 could act as a final filter.
The filter media used to construct the inner and outer filter elements 14, 12 can be the same or they can be different. In particular embodiments it can be advantageous that the material be different. For example, in the depicted embodiment the outer filter element 12 may be constructed of a material with greater average pore size than the material used to construct the inner filter element 14. In such an embodiment the outer filter element 12 would be primarily used to remove larger particulate matter, whereas the inner filter element could be primarily used to remove the smaller particulate matter. A variety of different material could be used in the construction of the inner and other filter element. For example, non-woven (e.g, melt blown material, wet laid glass fibers, cellulosic depth media) or micro porous membranes can be used to construct the filter media (e.g., nylon, poly(vinylidene diflouride) (PVDF), polyethersulfone, poly(tetrafluoroethylene) (PTFE), polypropylene, polyethylene, etc.). In one particular embodiment the outer filter element 12 is constructed of a material commercially available from Lydall Filtration, Manchester, Conn. having “D” series grade, a base weight of about 82 g/m2, thickness of about 0.45 mm, and mean flow pore of about 7.5 μm, and the inner filter element 14 is constructed of a micro porous membrane having an average pore size of about 0.2 microns. The materials can be chosen so that the filter arrangement 10 is suited for particular purposes and/or so that the filter has a particular geometric configuration. For example, the micro porous membranes in an alternative embodiment could alternatively have an average pore size of about 0.1 or about 10 microns.
Typically, the ratio between the outer diameter of the outer pleated filter element and an inner diameter of the outer pleated filter element is equal to or less than 1.5 to 1. For example, see the filter disclosed in U.S. Pat. No. 5,232,595 to Meyer. Although there is a mathematical relationship that suggests that the ideal relationship between the outer and inner periphery or diameter is 2:1 when known traditional pleats are used, in actual practice, a ratio of 1.5 to 1 leads to a more even pleat compression. When a 2:1 ratio is used, the outer pleats still show evidence of radial spreading, and an additional area gain can be realized with a multi-pleat. When a ratio of 1.5:1 is used, minimal radial spreading occurs and the use of a W pleat approach yields almost no practical gain in area. In the depicted embodiment d4 generally describes the inner diameter of the outer pleated filter element 18. The above-described configuration (
Referring to
The left side of
The right side of
In designing a filter product, it is commonly preferred to incorporate more than one layer of filter media with each layer having a different character to improve the overall filtration performance. However, if these two layers are co-pleated, then the filter area of the upper media will automatically be the same as the filter area of the lower layer. A co-pleated configuration does not allow for deviation from this 1:1 ratio. Depending upon the ultimate filter application, there may be a need for the prefilter area to be considerably greater or less than the final filter area. If the filter media are arranged instead as an inner and outer filter element, as previously described as concentric filter elements, then the ratio of the area of the prefilter media to the area of the final filter may deviate substantially from 1:1. A filter with concentric filter element using only traditional radial pleats will also limit the desired ratio to some prescribed amount. However, if a multipleat approach is used instead then other ratios can be realized. With any filter, other design constraints exist. The core size may be dictated by flow considerations. If the core is too small, it may not allow adequate egress of fluid flow from the element. If it is too large, then filtration area could be lost. The outer cage size will be dictated by space considerations. If it is too large, then it may not fit into the space reserved for it. Filters tend to be installed in locations where space is limited, and this design consideration is almost always present.
Employing nontraditional pleating configurations, which have been used in single filter element systems, to a concentric filter arrangement can be advantageous. In some embodiments it can result in successful combinations of different filtering media that are otherwise not possible or practical. For example, two very dissimilar filtering materials may be difficult to combine in a concentric arrangement employing a traditional pleating configuration (i.e., 1.5:1 ratio), as the useful life of each filter elements would be substantially different and may lead to failure of one filter element while the other filter element is still viable. Combining filter elements with substantially different useful lives can be undesirable, as the useful life of the filter system would be limited by the filter element with the shortest useful life. It is therefore typically more desirable to have the ability to tailor filter systems that combine multiple elements with similar useful lives. The present disclosure enables more of such combinations as the area of the pleated element in the inner and outer filter element can be varied more widely than would otherwise be feasible. In some embodiments, the surface area of the pleated element in the inner element is between 0.2 and 5 (in some embodiments, between 0.4 to 3; 0.5 to 2, or even 0.7 to 1.5) times the surface area of the outer element. The desired ratio will depend on a number of factors, including, for example, the target fluid to be filtered and properties of the filter media. Employing the principles of the present disclosure the ratio of diameters of the outer filter media and the inner filter media may be varied through a wide range (e.g., 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2.0:1, 2.2:1, 2.4:1, 2.6:1, 2.8:1, 3.0:1, 3.5:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1). Since the principles of the present disclosure enable the ratio in areas and diameters to be adjusted over a broader range, more material combinations can be used in the filter construction. Referring to
In example embodiments, a filter product with an inner filter element and an outer filter element may be constructed of materials as shown in Table 1 below. Ignoring the potential for support or media compression, the thickness of both pleat legs would typically be double the total thickness of the various supports and filter media.
The primary pleat contribution may be easily calculated from the following:
Pleat height=(Outer diameter-Inner diameter)/2
Pleat count=(Inner circumference)/(total media thickness both legs)
Area=Pleat height*2*Pleat count*filter length
The secondary pleat contribution is more complicated but calculation can be visualized graphically as a trapezoid where one of the vertical sides is orthogonal to the upper and lower horizontal sides. The lower and shorter side on the trapezoid would correspond to the circumference of the inner diameter of the filter element. The upper and longer side of the trapezoid would correspond to the circumference of the outer diameter. Such a trapezoid could be further subdivided as a rectangle and a triangle by drawing a line on the lower horizontal side but opposite of the orgothonal vertical side but parallel to the first vertical orthogonal side. The vertical orthogonal side would correspond the primary pleat height. The rectangle would correspond to the contribution of the primary pleat. The triangle would correspond to the portion of the secondary pleats. Theoretically, the triangle would represent pleat heights diminishing to the point of no height, which is not practical in reality. In U.S. Pat. No. 6,315,130, it was suggested that only ⅔ of the excess circumference (which is ⅔ of the difference between the upper and lower side of the trapezoid) could be used before the pleats became impractically short. The limit is empirical as it is a function of the pleat thickness, media pliability and other factors, but some limit will always exist so that same limit will be used for the calculations below. Although the secondary pleats will vary in height, for ease of calculation they may be represented by some average height. If pleat heights of all lengths could be used, then that height would be ½ the primary pleat height. However, since only the first ⅔ of the pleat heights can be used, and it is the shortest pleats that are eliminated, the average will be greater than ½ the primary pleat height For ease of calculation, ½ will be used.
Therefore the equations for Multi-pleat per U.S. Pat. No. 6,315,130 would be as follows:
Primary Pleat height=(Outer diameter−Inner diameter)/2
Primary Pleat count=(Inner circumference)/(total media thickness both legs)
Secondary Pleat height=½*((Outer diameter−Inner diameter)/2)
Secondary Pleat count=(Outer circumference−Inner circumference)*0.67/(total media thickness both legs)
Total Area=(Primary pleat height*2*Primary pleat count*filter length)+(Secondary pleat height*2*Secondary pleat count*filter length)
Table 2 below summarizes some examples that show that by varying the outer periphery of the inner filter element, it is possible to vary the ratio of areas for the multipleat design. Example 1 shows a conventional radial approach for a specific set of diameters for the inner and outer filter element. Examples 2 and 4 show how the multipleat can easily bracket the conventional radial pleat approach in terms of varying area. Example 3 shows that in order to vary the area ratio of a conventional radial approach, it is necessary to vary the overall dimensions of the filter. Varying the design in this manner can also lead to spreading of the pleats which are disadvantageous during assembly and use.
The above specification, examples and data provide a complete description of the manufacture and use of the composition of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended.
