FILTER WITH STAGED PLEATING
BACKGROUND
The present invention relates to filters, and more particularly to pleated filter elements and filter assemblies including pleated filter elements.
In order to remove contaminants from a flowing gas or liquid, filter elements and assemblies have heretofore been used which cause the medium to be filtered to pass through a filter material. In many of these filter elements, the filter material is in the form of a flat sheet. However, in some filter elements, the filter material has been pleated. As compared to filter elements in which the filter material is flat, pleated filter elements offer an increased filter surface area without substantially increasing the overall size and weight of the filter element.
Generally, in pleated filter elements, the size of the pleats has been uniform, i.e. only one pleat size has been used in a particular filter element. Such pleated filter elements may be formed into various shapes by spacing the pleats around a core element having that shape. However, supporting a filter element around a core element has the disadvantage of reducing the filter surface area available for contaminant removal.
SUMMARY OF THE INVENTION The present invention relates to a novel filter element having a septum with staged pleating in which the heights of successive pleats are related by a specified ratio as well as to a filter assembly incorporating such a filter element. Two particular pleat height ratios are discussed. Pleat sequences according to the pleat height ratios may be repeated about
the perimeter of a desired inner core. The septum may also include drainage layers on upstream and downstream of the filter material layer. BRIEF DESCRIPTION OF THE DRAWINGS
FIGURE 1 depicts a three-pleat pleating sequence according to an embodiment of the present invention.
FIGURE 2 depicts a four-pleat pleating sequence according to an embodiment of the present invention.
FIGURE 3 shows a cylindrical filter element incorporating a pleating pattern based on a pleating sequence according to the present invention. FIGURE 3 A shows a cross-section of the cylindrical filter element shown in
FIGURE 3 taken across the line "A"-"A."
FIGURE 3B shows a portion of the septum shown in FIGURE 3 A.
DETAILED DESCRIPTION The present invention relates to filter elements and assemblies that may be used in applications where higher filtration flow rates, lower retention
FIGURE 1 shows a three-pleat pleating sequence according to an embodiment of the present invention. The pleating sequence consists of a major pleat la and two minor pleats lb and lc (collectively "pleats 1"). Each pleat has two sides 3a and 3b. The pleats 1 may be made of a single- or multi-layer septum material which includes as a layer a filter material. An example of a suitable filter material is a polytetrafluoroethylene (PTFE) material produced by W.L. Gore & Associates of Newark, Delaware. The pleat height of any pleat in the sequence is measured as the shortest straight-line distance from the pleat's base 4 to the pleat's tip 2. In a pleating sequence according to the three-pleat embodiment of the present invention shown in FIG. 1, the pleat height of the major pleat la is shown as "A." The pleat heights for the minor pleats lb and lc are 2/3 of A and 1/3 of A respectively. Therefore, the pleat height ratio for the pleating sequence is 3:2:1. The
width of the base 4 for each pleat may be substantially the same and may be determined by the thickness of the single- or multi-layer septum material. Pleats 1 may be formed using a microprocessor-controlled knife pleater such as the Accordion Pleating Machine Model #R178PC manufactured by Karl Rabofsky GmbH. Although the tip 2 of each pleat is shown as a point, giving the pleat a "V" shape, the tip actually may be slightly rounded. The radius of the tip 2 may be determined by the characteristics of the implement used to create the pleats 1 in a sheet of filter material as well as the thickness of the filter material sheet. In embodiments of the invention, the pleat material may consist of multiple sheets. For example, the filter material sheet may be placed between drainage layer sheets. An embodiment including multi-layer pleats is discussed in greater detail in relation to FIGURE 3B.
FIGURE 2 shows a four-pleat pleating sequence according to an embodiment of the present invention. As in the embodiment shown in FIG. 1 , the pleating sequence has a major pleat 101a. The pleating sequence also has three minor pleats 101b, 101c and lOld. Each pleat has two sides 103a and 103b. The pleat height of any pleat in the sequence is measured as the shortest straight-line distance from the pleat's base 104 to the pleat's tip 102. In a pleating sequence according to the three-pleat embodiment of the present invention shown in FIG. 1, the pleat height of the major pleat 101a is shown as "A." The pleat heights for the minor pleats 101b, 101c and lOld are 3/4 of A, 1/2 of A and 1/4 of A respectively. Therefore, the pleat height ratio for the pleating sequence is 4:3:2:1. The width of the base 104 for each pleat may be substantially the same and may be determined by the thickness of the septum material.
As shown in FIG. 3, a filter assembly according to an embodiment of the present invention may also include an end cap 204a and 204b at each end of the filter element 207 (shown in FIG. 3 A). In embodiments of the invention, the end caps 204a and 204b may be attached to the septum 203, inner core 201 and/or outer guard 202 by methods of attachment suitable to the materials being used, the medium being filtered, the
contaminant being removed, and other application-specific considerations. For example, in different applications, the end caps 204a and 204b may be attached using one or more of the following: adhesives or epoxy; thermal, diffusion or ultrasonic welding; or mechanical fasteners. It may be desirable to attach the end caps 204a and 204b to the ends of the filter element in such a way as to create a seal that prevents leakage of the medium being filtered. The filter element 207 may also be encased in an outer support tube 205. The portion of the outer support tube 205 and outer guard 202 have been cut away in FIG. 3 to display the pleated septum 203 therein.
FIGURE 3 A shows a cross-section of the filter assembly illustrated in FIG. 3. The filter element may have an inner core 201 and an outer guard 202. The pleating sequence 206 may be repeated around the inner core 201 to form the septum 203. In particular, FIG. 3A shows an embodiment in which the septum 203 is formed using a pleating sequence 206 having three pleats with a height ratio of 3:2:1, similar to the pleats 2 shown in FIG. 1. Only a portion of the septum 203 is shown in FIG. 3 A; in embodiments of the present invention, the pleating sequence may be repeated such that the septum 203 completely surrounds the inner core 201.
A portion of a multi-layer embodiment of the septum 203 shown in FIG. 3 is depicted in FIGURE 3B. As shown, the medium being filtered flows from the side of the septum 203 proximate the outer guard 202 (the "upstream side"), to the bottom side of the septum 203 proximate the inner core 201 (the "downstream side"). In alternative embodiments, the flow direction may be reversed, i.e., the upstream side of the septum 203 may be proximate the inner core 201 and the downstream side of the septum 203 may be proximate the outer core 202. The septum 203 may include an upstream drainage layer 203a, a filter material layer 203b and a downstream drainage layer 203c. In FIG. 3B, the upstream drainage layer 203a has been cut away to expose the filter material layer 203b and the filter material layer 203b has been cut away to expose the downstream drainage layer 203c. The upstream and downstream drainage layers 203a and 203c may be made of
a woven or non-woven material with good porosity, such as glass, natural fibers, or polymeric materials (e.g., polyester, polypropylene or a polyamide) and may be in the form of an extruded mesh. Although the upstream and downstream drainage layers 203a and 203c are referred to as "drainage" layers, they may serve a structural support function in addition to or in place of their drainage function.
In other embodiments of the present invention, the septum 203 may not include upstream and downstream drainage layers 203a and 203c. Alternatively, the septum 203 may include additional layers. For example, the septum 203 may include a pre-filtering layer placed upstream of the filter material layer. The purpose of the pre-filter layer may be to remove contaminants substantially larger than the contaminants the filter material layer 203b is designed to remove from the medium. Removal of these substantially larger contaminants by a pre-filter layer may reduce clogging or obstruction of the filter material layer 203b. In an embodiment of the present invention, a upstream drainage layer 203a may also serve as a pre-filter layer. In an embodiment of the invention, the septum 203 may include spacing elements on the surface of the upstream side, the downstream side or both of the septum 203. The spacing elements may be placed so that spacing elements on adjacent pleats interfere or make contact when the adjacent pleats are moved together. Using the pleats 2 in FIG. 1 as an example, spacing elements placed on leg 3b of major pleat la may interfere with spacing elements on leg 3c of minor pleat lb. The spacing elements may be sufficiently spaced apart and of such size as to not significantly reduce the filtering area of the septum 203.
The filter element may have a circular inner core 201 and/or outer guard 202. However, in embodiments of the invention, the inner core 201 and the outer guard 202 may be rectangular or have different shapes. In an embodiment of the invention, the inner core 201 may have a different shape from the outer guard 202.
The septum may be created by pleating a sheet of filter material (and sheets of drainage layer material and/or sheets of material for other layers of a multi-layer septum), wrapping the sheet(s) into the shape required to fit around the perimeter of the inner core 201, and side-sealing the ends of the sheet(s). The sides may be sealed using an adhesive or epoxy; diffusion, ultrasonic or thermal welding; mechanical fasteners or the like. The sheet of filter material may be pre-expanded by soaking it in the medium to be filtered or another suitable solution before the sheet is pleated.
The inner core 201 and/or outer guard 202 may be formed from extruded polypropylene mesh, a metallic mesh or the like. The material forming the inner core 201 and outer guard 202 may be chosen based on the nature of the medium being filtered, the contaminant being removed, the thermal environment for the filtering application or similar considerations. For example, in high temperature applications, it may be necessary to use a metallic mesh inner core 201 and outer guard 202. The filter element may be used for inside-out flow, in which unfiltered medium flows from the inner core 201 to the outer guard 202 through the septum 203, or outside-in flow, in which unfiltered medium flows from the outer perimeter 202 to the inner perimeter 201 through the septum 203.
While the description above refers to particular embodiments of the present invention, it should be readily apparent to people of ordinary skill in the art that a number of modifications may be made without departing from the spirit thereof. The accompanying claims are intended to cover such modifications as would fall within the true spirit and scope of the invention. The presently disclosed embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than the foregoing description. All changes that come within the meaning of and range of equivalency of the claims are intended to be embraced therein.