Filter Module

Some of the objects of the invention have been set forth above. Other objects and advantages of the invention will appear as the description of the invention proceeds when taken in conjunction with the following drawings, in which:

FIG. 1 is an exploded view of the filter according to the present invention;

FIG. 2 is a perspective view of the fiber bundle, with a fragmentary enlargement of a small section of the top surface of the bundle;

FIG. 3 is a side elevation view of the fiber bundle shown in FIG. 2;

FIG. 4 is a fragmentary, enlarged cross-section of the circled section shown in FIG. 3;

FIG. 5 is a schematic view of the filter showing the flow path of gases therethrough;

FIG. 6 is an extreme fragmentary enlargement of a segment of the fiber bundle showing the path of the gas through the side wall of the fiber;

FIG. 7 is a schematic view of the filter in combination with a valving arrangement useful in changing filter modules;

FIG. 8 is a horizontal cross-section of the filter showing the eccentric relation of the fiber bundle to the cylindrical filter module; and

FIG. 9 is a fragmentary vertical cross-section, with parts broken away, of the filter.

Referring now specifically to the drawings, a filter according to the present invention is illustrated in FIG. 1 and shown generally at reference numeral 10. The filter 10 is comprised of three basic parts--a base 20, and filter module 40 and a filter element 60. The filter element 60 is sealed within filter module 40 and both parts are together disposable after the filtration capacity of the filter element 60 has been exhausted. Filter module 40 is positioned in the base 20 and thereby interconnects with a gas supply.

More specifically, base 20 comprises a housing 21 intended to be suitably mounted on a wall, cabinet or some other surface. A top holder 22 receives filter module 40 in a manner to be described more specifically below. A bottom holder 23 defines an annular threaded opening 24 which receives a two piece end cap 25 connected by a bolt 26. The space between the top holder 22 and bottom holder 23 defines an area into which fits filter module 40. Filter module 40 is inserted laterally into the area after which end cap 25 is tightened. Proper rotational alignment of the filter module 40 in the base 20 is achieved by mating an elongate groove 41 in the outer surface of filter module 40 against the longitudinally-extending edge 28 of housing 21.

Gas supply and gas exhaust conduits 29, 30 are interconnected into top holder 22 on opposite sides thereof. Base 20 may be constructed of various materials including, for example, aluminum, brass, stainless steel or various FDA approved plastics.

Filter module 40 comprises a cylindrical body 42, the top end of which is sealed by a top cap 43. Top cap 43 includes a gas inlet 44 eccentric to filter module body 42 and a gas outlet 45 concentric with filter module body 42. The filter element 60 is installed into the filter module 40 through the bottom opening, after which the bottom opening is permanently sealed closed by a bottom cap 46. Gas inlet 44 and gas outlet 45 are provided with rubber O-ring seals 47, 49, respectively, and seal against mating surface of the top holder 22, as is more particularly described below.

Referring now to FIGS. 2, 3 and 4, the filter element 60 is described in further detail. To be usable, the fiber bundle must be potted on one end to provide a sealed area between the outside and the lumen of the fibers. As is shown in FIGS. 2, 3 and 4, filter element 60 is comprised of a multiplicity of individual fibers 61, which may be of various porosities and sizes based upon considerations of rate of gas flow through the filter, particulate size and the like. The filter element 69 is typically packed to a density of 40%. The filter element is formed into a bundle arranging the fibers in a coherent, parallel array and then potting one end of all of the fibers onto a bed of polyurethane resin 62. Full details regarding this process can be found on page seven of the publication referred to above, entitled Technical Information, Fabrication & Handling--Hollow Fiber, March, 1985. After the resin is at least partially cured, the top layer of the resin 62 is sliced off, leaving a surface with exposed, open fibers 61 with the spaces between the fibers filled in with the resin 62. This is best shown in FIG. 2. The potting not only secures the fibers 61 into the required bundle, but the cured resin also supports the individual fibers with the lumens 63 (the hollow, central core of the fiber) in an open, substantially cylindrical configuration. The resin 62 also prevents collapsing of the fiber walls.

The enlarged view shown in FIG. 2 is an idealized one, but nevertheless illustrates that the fibers 61 are secured together into an array. The view in FIG. 4 illustrates that a cross-section through the resin 62 would reveal an irregular arrangement of the fibers 61, which are nevertheless securely attached together in sealing relation.

Referring now to FIG. 5, the simplified cross-section illustrates that the gas inlet 44 makes with a gas inlet 32 in top holder 22, and that gas outlet 45 mates with a gas outlet 33 in top holder 22. Filter element 60 is sealingly attached to the top 43 of filter module 40 in surrounding relation to gas outlet 45. The filter element 60 is asymmetrically arranged in the filter module 40 to provide room for gas inlet 44 and to permit adequate room for gas circulation and diffusion within filter module 40. See also FIG. 8. A pressure responsive check valve 51 is installed in filter module 40 in gas inlet 44. Check vale 51 is open only when gas under pressure is flowing through the valve. Any loss of pressure seals the interior of the filter module 40 against leakage of contaminated air into the environment.

As is also shown in FIG. 5 and FIG. 9, top holder 22 includes a pressure relief valve 35 which, upon activation, release pressure within filter module 40 and equalizes the pressure inside filter module 40 with the outside environment. Shutoff valves 80 and 81 are not part of the invention per se, but enable the filter module 40 to be isolated from the contaminated and filtered air before removal and replacement.

The physical characteristics of the fibers 61 have been described in detail above. By reference to FIG. 6, the basic flow pattern of a gas through a fiber is shown. As described above, each fiber has a wall thickness through which the pores define tortuous path. The twists and turns in the path provide tight corners, kinks and areas of reduced diameter with trap particles of a much smaller size than the nominal pore size in the fiber. In the view shown in FIG. 6, the flow is from the outside of the fiber 61 through the side wall and into the lumen 63. An arrangement to accomplish this flow pattern is shown in FIG. 7, where a vacuum pump 82 creates a negative pressure through the filter element 60 from the upstream to the downstream side of the fibers 61. A positive pressure pump could also be used on the upstream side to force gas through the filter element 60. In addition, gas flow can be reversed, so that contaminated air is passed into the lumen 63 of the fibers 61 whereby filtration takes place as the gas passes to the outside of the fibers 61. The unique, uniform pore size from one side of the fiber walls to the other permit the filtration to occur in either direction.

Determining the frequency with which the filter module 40 should be changed can be accomplished by metering the gas filtered through the filter 10, or simply at predetermined time intervals. To change the filter module, pressure must first be equalized between the interior of the filter module and the outside environment. Referring again to FIG. 5, valve 80 is first closed to discontinue the flow of contaminated gas. This will also close check valve 51, sealing the filter module and preventing contaminated air from escaping through inlet 44. Continued negative pressure on the downstream side of the filter pulls residual contaminated air through the filter element. Then, valve 81 is closed, discontinuing pressure on the downstream side of the filter element. Pressure, either negative or positive, is therefore trapped in the filter module 40. Pressure relief valve 35 is depressed, equalizing pressure. The positive pressure trapped in filter module 40 is released downstream from the filter element. Therefore, the vented gas is filtered, not contaminated, gas. Pressure relief valve 35 is preferably a Model No. 125 INS-P2-10 cartridge valve which will operate in a 2-way or 3-way mode. As is shown in FIG. 9, pressure entering the bottom of the valve holds the valve in a closed position with the bottom diaphragm 36 seated. Force on top of the main stem 37 unseats bottom diaphragm and lowers top diaphragm 38 into its conical seat, sealing off the exhaust. Gas flows through perforations in the bottom diaphragm, past the seat and out through a cross-drilled port which communicates with a port 39 in top holder 22. After release of pressure in filter module 40, end cap 25 is unscrewed. This permits filter module to slide down in the housing 21 far enough to clear top holder 22. Then, filter module 40 is removed from housing 21 by grasping it and pulling it laterally outwardly. Note according to FIG. 1 that the groove 41 in the side wall of filter module 40 slides along edge 28 of housing 21 and maintains proper alignment between these two elements. This is essential in order for gas inlet 44 and gas outlet 45 to seat properly.

A new filter element 40 is installed by aligning groove 41 with the edge 28 and inserting the filter module 40 laterally into housing 21. After insuring that the filter module 40 is properly mated, end cap 25 is tightened. Pressure exerted by the end cap 25 presses the O-rings 47 and 49 against the gas inlet 32 and gas outlet 33, respectively, of top holder 22.

A method and apparatus for microfiltration of gases is described above. Various details of the invention may be changed without departing from its scope. Furthermore, the foregoing description of the preferred embodiment according to the present invention is provided for the purpose of illustration only and not for the purpose of limitation--the invention being defined by the claims.