Patent ID: 12220656

DETAILED DESCRIPTION OF THE INVENTION

With reference to the drawings and in operation, the present invention provides a filter frame700with a removable inner frame assembly701for use with one or more filter element706. The filter frame700may be used within a clean room and for a method of constructing a clean room. All descriptions and variations used in describing the method may be applicable to the clean room itself, and visa versa.

In one aspect of the present invention, a system and a method for applying multiple filter elements into an air flow surface of a medically safe room and limiting air flow around sides of the filter elements including:providing a frame that supports at least two adjacent filter elements having two pairs of opposed sides, one pair of opposed sides along its length and a second pair of opposed sides along its width;the frame having at least one filter element separating support arms aligned to support adjacent filter elements;the at least one filter element separating support arm separated by an orthogonal bracing arm;the frame is formed with each filter element separating support arm being spaced between two adjacent filter elements, each filter element separating support having two parallel tracks separated by a raised panel extending the length of the two parallel tracks, and two parallel outside support arms are positioned at outer edges of the multiple filter elements, the two parallel outside support arms having at least one track with raised sides forming the at least one track;each orthogonal bracing arm having at least one track with raised sides along a length of each at least one track;the filter elements having four linear edges extending coplanar from sides of the filter elements along a bottom of each of the opposed sides of the filter elements with a width less than a width of a parallel track;placing a tape of elastic ultralow density polytetrafluoroethylene polymer having a specific density of greater than 0.10, greater than 0.20 or equal to or greater than 0.25 and less than 0.6 along the length of the two parallel tracks in at least one opposed filter element separating support arm;placing a tape of elastic ultralow density polytetrafluoroethylene polymer having a specific density of greater than 0.10, greater than 0.20 or equal to or greater than 0.25 and less than 0.6 along the length of the two parallel tracks in at least one opposed filter element separating support arm;placing sealant that is limited or not (as herein defined) off gassing along the at least one track in the two outside support arms and along the length of the at least one track in each bracing arm;inserting the four extending linear edges into each of the length of the two opposed filter element separating support arms and along the length of the at least one track in each bracing arm;the four extending linear edges compressing and conforming the tape in the two parallel tracks in at least one opposed filter element separating support arm to form an effectively air tight seal along every track; andplacing an elastically restraining cable on a face of each of the filter elements opposite to the four extending linear edges.

In the above method and system, the ultralow density polytetrafluoroethylene tape (often described hereinafter as the “ULDS tape”) is used only on the most critical support arms between adjacent filter elements that have two tracks. It is also desired that the ULDP tape be applied on the two parallel outside support arms, as described herein. Additionally, it is more preferred when the ULDP tape is used in every track used to support individual and collective arrays of filter elements, including the tracks in the support arms between adjacent filter elements, the two parallel outside support arms and the orthogonal bracing arms. These ULDS tapes are also “non-gassing” tapes in that there is essentially little (less than 0.1% by weight, or even less than 0.05% by weight) to no low molecular weight materials (including solvents) that will emit from the polymer. Additionally, the invention is to replace existing technologies using a gel type product that cannot be cleaned, even with strong cleaning agents to kill a host of microbes, including bacteria, fungi, viruses and especially COVID-19, and other bad actors as well. In a pharmaceutical application, it is needed to wipe down all surfaces constantly and thoroughly. And the uniformly commercially used gels don't lend themselves chemically to that type of aggressive cleaning. Also, the present inventive technology comes out of a fully-ready container, such as bag, box, carton, package or the like, and is ready to install. On the other hand, gel has to be poured into the track and then there can be a set-up time for the gel, and the workers have to wait a day or more for it to cure before a filter can be placed into the track. Once the present technology ultralow density PTFE tape or ULDS molding strip is placed into the track, it can be used immediately for filter installation and use. The fact that there is no off-gassing from the ultralow density PTFE molding or tape further accelerates the ability to use the facilities and reduce deleterious, toxic or annoying odor in the work environment. Because of this case of use, the downtime in critical facilities is very minimal. To replace gel, it is necessary to close down that part of the plant or facility that needs the filter (and contemporarily) and the gel replaced, then workers have to remove all the gel (which may then be a hazardous waste). This takes many days depending on the number of filters. For example: 12 gel tracks filled with gel would take one week to scrape and prep the track then pour the gel and then still wait at least 24 hours for it to cure. The same process with the present technology using ULDS tape or molding would be 5-6 hours total.

A method is described for applying filter elements into an air flow surface of a medically safe room (other clean rooms may also benefit from this method and structure). The safe room or clean room limits air flow around sides of the filter elements, preventing ingress or egress of contaminated air from the room. The method provides a frame that supports at least two (this includes three, four or more filter elements) adjacent filter elements. The filter elements are usually in rectangular structures, with a main surface, an opposed surface, two opposed long sides and two opposed shorter sides. The filter element having two pairs of opposed sides (the long and shorter sides), one pair of sides along the length of the filter element and a second pair of sides along the width of the filter element. The frame having pairs of filter element separating support arms that are aligned to support adjacent filter elements. Support arms between adjacent filter elements will have two tracks, one each to engage with extensions off the filter elements that are inserted into the tracks, as later explained in greater detail. There are pairs of the support arms between adjacent filter elements will have two tracks pairs when there are at least three filter elements. When there are only two filter elements, there would be on a single filter element separating support arm. The filter element separating support arms are separated and structurally supported by orthogonal bracing arms.

Each filter element separating support arm is spaced between two adjacent filter elements having two parallel tracks separated by a raised panel extending the length of the two parallel tracks. The two parallel outside support arms (adjacent a long side of the filter elements at the ends of an array of multiple filter elements) have at least one track with raised sides. Each orthogonal bracing arm has at least one track with raised sides along a length of each at least one track. Only one track essential (a second is redundant) as these bracing arms may be supporting only a single filter element, while adjacent sides of the filter element separating support arm will support two adjacent filter elements.

The filter elements have four extending linear edges (these may be referred to as knife edges, edge extensions, extending arms or the like) along a bottom of each of the opposed sides of the filter elements with a width less than a width of a parallel track. As the filter elements are preferably rectangular, the four extending linear edges will also match the geometric shape of the filter element, and in the preferred case, also form a rectangle.

The method includes placing a tape of elastic ultralow density polytetrafluoroethylene polymer having a specific density of greater than 0.10, greater than 0.20 or equal to or greater than 0.25 and less than 0.6 along the length of two tracks in at least one opposed filter element separating support arm, along the at least one track in the two outside support arms and along the length of the at least one track in each bracing arm. The four extending linear edges are inserted into each of the length of the two opposed filter element separating support arms and along the length of the at least one track in each bracing arm.

The four extending linear edges compress and conform the tape to form an effectively air tight seal along every track; and

The method fundamentally may conclude by placing an elastically restraining cable on a face of each of the filter elements opposite to the four extending linear edges.

The method may particularly use the elastic ultralow density polytetrafluoroethylene polymer has a specific density of greater than 0.10, greater or equal to 0.20, or greater than 0.30 and less than 0.55. The method includes installing the system that allows for applying and tightening restraining cables that are attached at opposite ends to tension springs secured in turn to a stable support element of the frame.

The tape is relatively thick for what is considered a tape, and is at least ⅜ inch up to 1.25 inches in thickness and width, with ¾-inch by ¾-inch being typical.

The method is preferably also practiced wherein a previous set of filter elements is first removed from the frame by lifting used filters off the frame, physically peeling exhausted elastic ultralow density polytetrafluoroethylene polymer out of all tracks, replacing exhausted tape with virgin elastic ultralow density polytetrafluoroethylene polymer tape, and then applying unused filters onto the frame and placing an elastically restraining cable on a face of each of the filter elements opposite to the four extending linear edges. An important aspect of the invention is the coherence of the described ultralow density PTFE tapes, which form the necessary air seal at contact points between the filter elements and the frame, is that the used tape on used filters can be physically stripped (even just peeled) off the tracks in the frame. The tape therefore appears to only lightly adhere to track surfaces, but rather merely conforms to the filter element extensions and the tracks to form an air seal, without adhering contact points so strongly that significant residue would remain on the surfaces of the track.

The method for replacing tarnished or exhausted filters is performed wherein a previous set of filter elements is first removed from the frame by lifting used filters off the frame, physically peeling exhausted elastic ultralow density polytetrafluoroethylene polymer out of all tracks, replacing exhausted tape with virgin elastic ultralow density polytetrafluoroethylene polymer tape, and then applying unused filters onto the frame and placing an elastically restraining cable on a face of each of the filter elements opposite to the four extending linear edges.

A clean room with a replaceable filter element system includes:a frame that supports at least two adjacent filter elements having two pairs of opposed sides one pair along its length and a second pair along its width;the frame having pairs of filter element separating support arms aligned to support adjacent filter elements;the pairs of filter element separating support arms separated by orthogonal bracing arms;each filter element separating support arm spaced between two adjacent filter elements having two parallel tracks separated by a raised panel extending the length of the two parallel tracks, and two parallel outside support arms having at least one track with raised sides;each orthogonal bracing arm having at least one track with raised sides along a length of each at least one track;the filter elements having four extending linear edges along a bottom of each of the opposed sides of the filter elements with a width less than a width of a parallel track;a tape of elastic ultralow density polytetrafluoroethylene polymer having a specific density of greater than 0.10, greater than 0.20 or greater than 0.25 and less than 0.6 positioned along the length of the two tracks in at least one opposed filter element separating support arm, along the at least one track in the two outside support arms and along the length of the at least one track in each bracing arm;the four extending linear edges inserted into each of the length of the two opposed filter element separating support arms and along the length of the at least one track in each bracing arm;the four extending linear edges having compressed and conformed the tape within the length of the two tracks in at least one opposed filter element separating support arm, along the at least one track in the two outside support arms and along the length of the at least one track in each bracing arm to form an effectively air tight seal along every track; andan elastically restraining cable on a face of each of the filter elements opposite to the four extending linear edges.

A review of the Figures will assist in a further understanding and appreciation of the details of the present invention.

FIG.1is a perspective view100of ceiling filter elements112secured to a frame110for use as part (in this case a ceiling or roof) of a clean room (not shown). About each filter element112is shown what is referred to as the long side108and the short side102. Cables104used to maintain contact pressure between the filters112and the frame110are shown spaced apart on each filter element112.

FIG.2is a side view200of a filter element202secured by a spring212tensioned cable204to each filter element separating support210. The cables204are connected to the tensioning spring212through a physical connector such as a hook and loop216(or hook and eye, hook and holed plate, bolts, post and hole, etc., physical connectors). The tensioning spring212is connected to the filter element separating support210through a similar (but not necessarily identical physical connector214(here shown as a hook and hole bolted connector). One of the tracks or troughs in the filter element separating support210is shown with the tape208deformed by insertion of one of the four extending linear edges inserted into each of the length of the two opposed filter element separating support arms (here because of edge view of the length of the two opposed filter element separating support arms, only the end view of the filter element separating support210is seen). Element220is the raised separation plate between troughs in the filter element separating support210.

FIG.3is a perspective exploded view300of tensioning cable supports304with tensioning springs312, a filter element302, four joined ULDP tape strips308and a frame322configured to support and connect two separate filter elements302(only one shown). The frame322has troughs310separated by the raised separation plate320. The tape308is seated onto the troughs310and the four extending linear edges are inserted into each of the length of the two opposed filter element separating support arms and the troughs324on the orthogonal support arms.

FIG.4is a perspective view400of four unassembled filter elements402. The four extending linear edges406are shown on each of the filter elements402.

FIG.5is a perspective partial view500of a ratcheting lifting system and/or cable attaching system for filter elements502on frames536. The ratcheting system and other elements are addressed by the following key:500Filter under load and load transfer device502Filter body504—Load transfer cable506—Low Density Sealant510—Gel Track with Low Density Sealant510a—Gel Track with Low Density Sealant512—Load Spring520—¼″ 20-Treaded track for installation of SaddleFIG.2(214)530—Load installation stabilizer532—Load Tensioner Handle grip533—Load Tensioner ratcheting grip540—Load Tensioning rod534—Load Tensioning transfer release trigger.

The repeated squeezing of the load tensioner Handle grip532and the load tensioner ratcheting grip533ratchets the load installation stabilizer along the load tensioning rod. Although the troughs or tracks510and510aare referred to as “gel tracks,” this is merely previously existing structure into which the ULDP tapes are placed in the practice of the present invention.

As previously noted, other sealants may less preferably be used in the end support arm troughs or tracks538and the short side tracks or troughs510a. If filter elements are put into an end-to-end (rather than or in addition to side-by-side) orientation, ULDP tape may be placed into tracks510,510aand538.

The unique finding that ULDP tape may be used as the sealant is not only surprising, but the level of benefit and performance of the ULDP tape is unexpected.

Regular density (e.g., >7.0-1.50 specific gravity) materials are good sealants in other specialty areas, and even low-density polytetrafluoroethylene materials has limited use in other technical areas. For example, while chemical attack or extreme temperature might not leave any choice besides PTFE (these conditions are not present in medical clean rooms), there are some disadvantages to the material that could affect projects in other areas. Strong chemical disinfectants are prevalent in medical clean rooms. That product does not lend itself to temperatures above 600° F.

Higher Hardness

Virgin PTFE's hardness is 55 Shore D, which is much harder than a typical Nitrile O-Ring at 70 Shore A, which is a softer scale. The higher hardness negatively affects sealability, as the material doesn't conform the mating hardware surfaces as easily.

Leakage Rate

While rubber O-Rings might conform to “as machined” surfaces, standard PTFE sealants may require post-process surface finish improvements to control leakage to acceptable levels. This cannot be easily performed on the filter elements and frames discussed herein

In general, under normal conditions, the leakage rate for a standard specific gravity and normal density PTFE O-Ring will be higher than any elastomeric compound, especially those used as sealants. These normal and generally better chemical classes of sealants include polyurethanes, polysiloxanes (and other silicone polymers), polyacrylates, synthetic rubbers and synthetic elastomers (e.g., typically ethylenically unsaturated monomer polymers such as isoprene, polybutadiene, acrylonitrile, styrene and the like).

The use of a PTFE O-Ring is therefore not generally recommended for applications that don't require extreme temperature or severe chemical conditions, which clean rooms do not.

Inelasticity

PTFE's nature as an inelastic material means that reuse or multiple installations of the same seal will not be possible. Unlike rubber compounds, PTFE will not return to its original shape and cross-section once deformed during installation and use. That means PTFE O-Rings or tapes or beads are typically only recommended for static face seal or flange type configurations that are not actively engaged and disengaged. This is in contrast to the replaceable connections for filters on clean room air flow systems which must be changed regularly and tend to be used in rapid assembly and rapid disassembly situations.

For example, a PTFE O-Ring or bead would not be recommended for a chamber door seal that needs to be opened and closed frequently, as the O-Ring would likely have to be replaced after every use.

A reused PTFE O-Ring or bead may look and perform similarly to a standard rubber O-Ring suffering from extreme compression set. But unlike rubber, this compression set occurs after only one use.

More often, PTFE O-Rings are found in flange gasket type applications where the seal will remain static and undisturbed until the next service interval.

It is surprising that the narrow class of ULDP tapes have been found to be useful in the attachments of filter elements to frames in clean room environments because of some of these properties that were considered deficiencies in other environments. For example, the fact that ULDP tapes permanently deform is acceptable in the clean room filter setting, as the filters are not frequently opened and closed or placed and removed, and when they are removed, they are always replaced. The non-adherent properties of ULDP tapes would be expected to reduce scaling quality, but because the tape readily deforms yet retains its structural integrity, the tape forms a good seal on the first insertion of the filter edge extensions (e.g.,306inFIG.3.

The non-adherence also allows for physical stripping or manual peeling of the tape when disassembly of the clean room or removal of the filter takes place. Minimal or no special cleaning (degreasing, scrubbing of decomposed polymer, sludge removal, solvent washes and the like) is seldom needed. No more than standard sanitation wiping (using 90% by weight or above of isopropyl alcohol) is typically necessary when changing filters.

ULDP tapes are commercially available from Three Square Solutions, Inc. as “UltraLDS™ ULDS tape. The dimensions of the tape should be at least 0.5 inches by 0.5 inches (1.25 cm×1.25 cm) in diameter, with the length selected according to dimensions of the filters and frames. Preferably the dimensions should be 1 inch by 1 inch (2.5×1.5 cm), 1.5×1.5 inches (3.8×3.8 cm), and variations of all dimensions between 0.5 inches (1.25 cm) and 6 inches (15.3 cm) useful. Tapes are also available from Technetics Group, a subsidiary of Enpro Industries Inc.

A Nov. 29, 2012 Bulletin (submitted with this Patent Document to the USPTO, and as with all documents cited herein, is incorporated in its entirety by reference) from Camfil™ clean air solutions discusses the complexity, difficulties and benefits of gel sealants (as are today used in attaching HEPA (high efficiency particulate arresters or air filters) in commercial environments, specifically discussing knife edge insertion into troughs containing gel (with both silicone and polyurethane gels discussed). Problems include oozing or spreading of the gels beyond desired limits in the devices or even outside the devices. The need for intensive cleaning of areas where the gel has been used, if those areas are to be used again, and the like.

The unique properties of ULDP tapes and their first time use in the field of the present invention sealing knife-edge connections between HEPA filters and gas-tight clean room and especially medical clean room environments has provided a long-sought need in the field. The ULDP tapes have been defined as PTFE (polytetrafluoroethylene) tapes, but copolymers of PTFE may also be used as long as the resulting polymer retains off-gassing and preferably non-stick, cohesive and chemically resistant, as is monomeric PTFE polymer.

In reviewing the graphic representations of tests for off-gassing, the following explanation of those figures will be helpful. The basis for both outgassing tests are the Intel protocols of 50 C for 30 min. As noted in the Outgassing Analysis Notes, the following are the same:1) Retention time is +/−0.2 min2) n-decane was used as a standard for both tests. The test detection limit is 0.1 ppmw (parts per million by weight) for both tests.3) The amount of total outgassing includes all peaks detected.

The chromatograph,FIG.2on both reports, is a two dimensional x, y, graph. The horizontal x axis is the time at which a substance was detected, and a peak generated. The specific time a peak occurs identifies the substance. The vertical y axis, or area under the peak, is indicative of the amount of a specific substance present. On the graphs this referred to as abundance.

The SolidSeal™ gel chromatogram (page 5,FIG.2) shows peaks so small they cannot be identified. The Total Outgassing Compounds (page 6, table 1) is 0.1 ppmw (parts per million by weight).

The WM Plastics product off-gasses a number of unfavorable compounds (table 1) 2200 times that of Solidseal™ gel. It becomes readily apparent when comparing the two reports that Solidseal™ gel is the superior product.

One aspect of the benefits of the present invention is clearly displayed in graphs comparing commercial materials and the materials used in the practice of the present invention.

FIG.6Ais a chromatogram of a control run with no off-gassing materials present, showing progressive emission results for 35 minutes. There are zero recorded abundancies (off-gassed materials measured in units of parts per million by weight). There is a system meaningless display of less than 200,000 ppmw at 26+ minutes.

FIG.6Bis a chromatogram of a run on materials used in the practice of the present invention with modest off-gassing materials present, showing progressive emission results for 35 minutes. As can be seen, there are three sharp (single compound) peaks with abundancies between 400,000 and 800,000 ppmw. There are three other sharp peaks at about 200,000. Peaks (single compounds off-gassed) at 200,000 and less are considered insignificant. The system meaningless display is still present at less than 200,000 ppmw at 26+ minutes.

FIG.6Cis a chromatogram of a run on SoftSeal™ urethane gels materials used commercially in the field of practice of the present invention with extremely high off-gassing materials present, showing progressive emission results for 35 minutes.

There are six broader peaks (extended released materials) with abundances over 2,000,000. Not only are there more peaks, but the amount of materials evidenced at each peak are multiples of those shown by low-density ePTFE materials shown inFIG.6B. The system meaningless display is still present at less than 200,000 ppmw at 26+ minutes.

FIG.6Dis a chromatogram of a run on Easy Pour™ urethane gels materials used commercially in the field of practice of the present invention with both high off-gassing materials and large numbers of off-gassed materials present, showing progressive emission results for 35 minutes. This graph must be cautiously evaluated with respect to the information inFIG.6Bbecause of the different scales used for the abundances. Not only does the Easy Pour™ gel have two sharp peaks over 900,000 ppmw, but there are also about four additional peaks over 700,000 and at least three peaks over 300,000. The system meaningless display is still present at less than 200,000 ppmw at 26+ minutes.

The present invention therefore enables provision of a low off-gassing composition with five or fewer abundance peaks between 300,000 and 800,000, and even four or fewer (exactly three) abundance peaks between 300,000 and 800,000 within 20 minutes at 50° C. The system meaningless display is still present at less than 200,000 ppmw at 26+ minutes, and even exactly three abundance peaks between 300,000 and 800,000 within 20 minutes at 50° C.

Removable Inner Frame Assembly

In some situations, the filter elements112,202,302,402,500may need to be removed and replaced or reinstalled. As described above, the filter elements112,202,302,402,500may positioned within a frame110,324. A gel or tape within the frame110,324may be configured to receive a linear edges extending downward from the outer edges of each filter element112,202,302,402,500and creating a seal therebetween. In some instances, over time, the gel and/or tape may deteriorate and need to be replaced. In other instances, the filter elements112,202,302,402,500may have to be replaced.

In prior art systems, if a filter element112,202,302,402,500is removed by simply lifting the filter element112,202,302,402,500from the frame110,324the integrity of the gel or tape may be affected or degraded. If the filter element is then placed back in the frame, the seal between the filter element112,202,302,402,500and the gel or tape may not be effective or sufficient to reseal the filter.

With particular reference toFIGS.7-11,12A-12F, and13A-13Fin one aspect of the present invention, a frame assembly700with a removable inner frame assembly701and a main frame702is provided. In the illustrated embodiment, the removable inner frame assembly701includes an inner frame704. The frame assembly700may replace the frame110,324in the above-described embodiments. Alternatively, the removable inner frame704may be configured to work with the frame110,324in the above embodiments. In specific applications, e.g., a clean room, the main frame702may be installed over all or substantially all of the room. Alternatively, a number of main frames702may be used to cover the room.

With reference toFIG.7, the main frame702may be configured to support a plurality or bank of filter elements706. Each filter element706may have an associated inner frame704. For example, in the illustrated embodiment, the main frame702may support up to 4 filter elements aligned linearly (FIG.7). It should be noted that the main frame702may be provided in any configuration (e.g., in a 2 by 2 configuration) or configured to support a different number of filter elements706.

The frame assembly700may include a main frame702within an opening708associated with each filter element706. In the illustrated embodiment, the frame assembly700includes four removable inner frames704. Each removable inner frame704is associated with one of the filter elements706.

With specific reference toFIG.13A, each inner frame704having a plurality of sides726. Each side726have a first end728and a second end730. As shown, the first end728of each side726is connected to a second end730of another (or adjacent) side726. The length of the sides726is dependent upon the size of the associated filter elements706.

As shown inFIGS.8, and12D, each side726has a pair of opposing legs710extending from a bottom711forming a u-shaped channel712extending around an outer perimeter of the inner frame704.

The inner frame704may be formed from one or more pieces of extruded aluminum which may be fastened together by any appropriate means or fasteners, such as brackets, screws, rivets, nuts and bolts, clips, a combination thereof and the like (see below). The sides728of the inner frame704form the corners of the inner frame704. In the illustrated embodiment ofFIGS.7-9, both the inner and outer edges are linear and meet at right angles.

Alternatively, the removable inner frame704may be formed as a unitary piece, such as by casting. In the illustrated embodiment shown inFIGS.12C-12E, the outer edge of each corner may be rounded.

With particular reference toFIGS.16A-16B and17A-17B, in other embodiments of the present invention, the inner frame704may be modular. For example, in the illustrated embodiment, the inner frames704may be composed of u-shaped side members748and corner pieces750. This modular arrangement allows the sides726of the inner frame704to be cut from standard lengths to fit particular filter elements. The inner frame704may then be assembled using the cut-to-length side members748and corner pieces750. As shown, the corner pieces750may have different shapes, for example, rounded corners (FIGS.16A and17A) or 45 degree corners (FIGS.16B and17B). In some embodiments, the corner pieces750may include integral clips, located, for example, along the bottom surface (not shown) to connect the corner pieces750at each end to one of the side members748(FIGS.16A and16B). In other embodiments, a separate splicer or clip752may be used to connect the side members748to the corner pieces750.

With specific reference toFIG.8, the removable inner frame assembly701includes a bottom sealant layer712attached to a bottom surface718of the bottom711inner frame704and a top sealant layer716located within the u-shaped channel712.

In one embodiment, the bottom sealant layer712includes a sealant720embedded in a substrate722. Generally, the cross-section of the sealant720may be larger than the substrate722. In other words, the substrate722may be enclosed entirely within the sealant720. Alternatively, the substrate722may be located at or near the top of bottom of the sealant720. The sealant720may be a two-part urethane or silicon gel. Such sealants are design specifically to act as a sealant in clean room environments. However, as a gel these sealants are not effective when filter elements need to be repeatedly removed and replaced. The gel breaks apart and loses integrity affecting the effectiveness of the seal.

One such gel is available from Dow under the name DOWSIL™ 3-4207 Dielectric Tough Gel Clear-Green. The bottom sealant layer712may be affixed to the bottom surface718of the removable inner frame704via a series of fasteners732. The substrate722may be made for an absorbent material such as a twill material. In one embodiment, the twill material may be composed from, at least partly, cotton. The sealant720may have a cross-sectional area that is larger than the substrate722. The substrate722assists in maintaining the integrity of the bottom sealant layer712and may assist in maintaining the bottom sealant layer712attached to the inner frame704.

The top sealant layer716may be composed of a urethane or silicon base gel or tape, a Teflon based sealant, ultralow density polytetrafluoroethylene tape (see above), or other appropriate sealant material. The top sealant layer716is configured to accept or receive the lower or knife edge724extending from the bottom surface of each filter element706. This arrangement allows the filter elements706to be repeatedly installed and uninstalled without catastrophic failure.

The inner frame704along with the bottom sealant layer714and the top sealant layer716may be preassembled and stored until needed. A bottom cover (not shown) and a top cover (not shown) may be utilized to protect the bottom sealant layer714and the top sealant layer716, respectively prior to usage. The removable inner frame assembly701may be used in new installations or used to replace the sealant gel in old installation.

To install a filter element706using the removable inner frame assembly704, the bottom cap is first removed. The removable inner frame assembly704may then be positioned within the main frame702. The top cover may then be removed and the filter element706installed.

Although not shown inFIGS.7-11,12A-12F, and13A-14F, a spring-based cable system may be utilized (see above) to cinch down each filter element706. The spring-based cable system may be coupled to the main frame702or the removable inner frame assembly701.

The removable inner frame assembly701may also be used in old installations in which the gel within the frame has failed and needs to be replaced and/or the filter elements must be removed and reinstalled or replaced.

To replace an existing filter in an older installation, the older gel needs to be removed. This may be a difficult and time-consuming process. For example, some gel must be removed or dissolved using 91-99% isopropyl alcohol. After the gel is removed, the surface of the frame must be cleaned before new gel is poured into the frame. Prior art gels must be activated with a catalyst or mixed in a 1:1 ration then poured within the frame. This process is prone to errors and accidents and some gels have a 16-36 hour curing time before the filter element can be installed.

The preassembled removable inner frame assembly704of the present invention may be installed very quickly. The bottom sealant layer714does not require any preparation at the installation site and may have a shelf life of up to 2-3 years based on storage conditions.

Further, once installed, the combined filter element706and removable inner frame704may be lifted out of the main frame702. The bottom sealant layer714formed by the substrate722and the sealant720may lifted along with the filter element706. The combination of the sealant720and the substrate722helps ensure that the entire bottom sealant layer714is removed from the main frame702. The removable inner frame assembly701may be reused or a new preassembled removable inner frame704may used without it being necessary to clean the upper surface of the main frame702.

In another aspect of the present invention, the removable inner frame assembly701may include an adjusting means734for allowing the connected first and second ends728,730of adjacent sides726of the inner frame704to be adjusted. In some instances, a filter element706may not fit easily within the u-shaped channel712of the inner frame704. This may be due to warping or misalignment of the filter element706or other reasons. The adjusting means734allows the sides726of the inner frame704be adjusted, for example, the position of one of the legs710of one of the sides726may be adjusted to accommodate the filter element706. Or the positioned of one of the sides726may be adjusted related to the connected or adjacent side726. In one embodiment, the adjusting means736is provided by an aspect of the inner frame704. For example, the inner frame704may be configured or designed to allow the inner frame704to be physically adjusted or stretched to accommodate the filter element706.

In another embodiment, the sides726of the inner frame704may form rounded corners (seeFIGS.12E-12F), or may include a 45 degree corners (seeFIG.14). Alternatively, the legs710of the sides726may end prior to the corner(s) leaving the corners open (seeFIG.15). These modifications to the corner may form at least part of the adjusting means and allow for the inner frame704to be adjusted or otherwise accommodate the filter element(s)706.

In other embodiments, the adjusting means734may be formed by the modular side members748and corner pieces750(and splicers/clips752if used).

In another embodiment, the adjusting means734includes an adjusting mechanism736as shown inFIGS.13A-13F. In the illustrated embodiment, the sides726of the inner frame704are not directly connected or fastened to one another but may be slidably connected to one another by the adjusting mechanism736. As shown, the removable inner frame assembly701may include an adjusting mechanism736located at each corner or junction between two adjacent sides726of the inner frame704.

With specific reference toFIGS.13B-13C, each adjusting mechanism736may include a bracket738with a first end740and a second end742. The first end740of the bracket738may be coupled to the first end728of one of the side726of the inner frame704and the second end742of the bracket738may be coupled to the second end730of an adjacent side726of the inner frame704.

Each of the first and second ends740,742includes at least one aperture744. The at least one aperture744on at least one of the first and second ends740,742is slotted or elongated. Respective fasteners732, for example, a bolt or screw and nut, may be used to fasten the bracket(s)736to the inner frame704through apertures746. The elongated or slotted apertures744allow one of the sides726to be moved or adjusted relative to the adjacent side726.

It should be noted that the fasteners732used to connect the bracket ends740,742to the sides726of the inner frame704may be the same fasteners732used to fasten the bottom sealant layer714to the inner frame704(seeFIG.13F). Alternatively, a different set of fasteners may be used.

The foregoing invention has been described in accordance with the relevant legal standards, thus the description is exemplary rather than limiting in nature. Variations and modifications to the disclosed embodiment may become apparent to those skilled in the art and fall within the scope of the invention.