Gas separation – Combined or convertible – In environmental air enclosure
Reexamination Certificate
2001-01-31
2001-08-07
Bushey, C. Scott (Department: 1724)
Gas separation
Combined or convertible
In environmental air enclosure
C055S484000, C055S502000, C055S508000, C454S187000
Reexamination Certificate
active
06270546
ABSTRACT:
FIELD OF THE INVENTION
This application relates to construction of clean rooms, and more particularly HEPA, ULPA and like high efficiency air filter systems for clean rooms. Clean rooms are enclosed spaces wherein the ambient air is repeatedly filtered to be substantially free of particulates, e.g., installations in which air is highly filtered to maintain an absence of particulates larger than 0.3 micron size, with HEPA filters, or larger than 0.12 micron size with ULPA filters. The term “HEPA” will be used herein to refer to either or both of HEPA and ULPA filters and other like high efficiency filters. Clean rooms are commonly used in the pharmaceutical, medical and electronic industries.
BACKGROUND OF THE INVENTION
Typically, an array of filter units is disposed above or to the side of a clean room. The term “clean room ceiling” herein refers to either an overhead array, or a to-the-side, sidewall array of filter units. In either case the room air is collected, recycled, and brought under pressure to the filter units. A volume of air to be filtered is typically pressurized on the upstream side of the filter unit to enable flow through the filter media. The term “plenum” herein refers to that space in which air is at a relatively higher pressure before flow through the filter media than on the outlet side of the filter. In a large filter installation the plenum is a large volume space above the clean room ceiling. In a small installation, such as a bench apparatus, the filter unit is typically combined in a housing with a fan, which serves to pressurize the air for through-filter media flow. The plenum-contained, pressurized air passes through the rear face of the filter units, through the filter media within the filter units and to the front face of the filter units for reintroduction into the clean room or toward the bench.
Because the filter units are of relatively limited size, a typical unit being only two feet by four feet, and the frequent need to cover a greatly extended area over a clean room, often the size of several football fields, multiple ones of the filter units are mounted adjacent one another in a laterally and longitudinally extended array, and the array sealed against leakage of unfiltered air from the plenum. The filter array mounting and sealing challenge has been met in the past by erecting extensive grids, suspended from above, onto which the filter units are placed. These grids often take the form of troughs with the individual filter units being fitted into a given rectangle of the grid with a projecting portion of the filter units being immersed in a gel sealant carried in the trough. The sealant and filter unit portions cooperate to block air flow from the plenum from entering the clean room except through the filter units. The grid troughs have a certain width, which increases the lateral spacing between filter units, ironically increasing the paths for sideflows of unfiltered air. In addition, the trough width reduces the proportion of filtered air area in the clean room ceiling, and induces turbulent air flow between the filter units, causing vibration.
Gel sealants to be effective must retain some elasticity or capacity to flow, despite years in place, so as to continually bear against the filter unit portions in the trough despite aging of the gel and vibration of the filter units. Replacement of the HEPA filter units as they become inefficient is a burdensome task. The individual units must be lifted up and away from the gelatinous mass in the troughs sufficiently to clear the trough edges, tipped or somehow angled so as to pass through the grid opening defined by the troughs, and carried out of the grid. Clinging gelatinous sealant can be messy. The installation of the new filter unit repeats these steps in reverse. More gel sealant may need to be added; these gels are quite expensive.
In U.S. Pat. No. 4,883,511 to Gustin et al, a clean room ceiling system is shown which uses gel sealants to seal filter units held in a vertically staggered array to support each other without use of a planar grid of troughs. In U.S. Pat. No.5,329,739, the patentee Madl describes a clean room filter system in which clusters of four filter units are supported together at the intersection of their respective comers by a disk overlapping each comer, the disk depending from a support surface such as a ceiling. Gel sealant carried on sealing strips seals the filter units against unfiltered air leakage. Mini grid assemblies have been proposed in which four filter units are supported on a common grid section, the grid section being supported from above by rods at corners of the grid section in German No. 3719734 A. In the parent application of this application, now U.S. Pat. No. 5,871,556, individually supported filter units were first disclosed; these used a suspension bracket within the filter unit to anchor to a fastener that depended from the ceiling or other support so that the filter units could be simply pressed into place from io below the ceiling without disturbing the other filter units adjacent.
BRIEF SUMMARY OF THE INVENTION
The present invention provides a different support system for individually supported filter units, one using in a preferred mode a series of fastener pins that engage a suspension support such as a horizontal plate carried on a suspension rod to support the filter units by an outturned flange on the filter unit frame. The fastener pins are carried with the filter units for ready assembly with the suspension support by a simple insert and rotate operation against the biasing force of a compression spring. The present invention affords the same superior individual self-suspension advantage of the parent application invention in an even less costly way, and offers increased installation ease as well. Thus the invention provides a number of improvements in clean room technology. The invention clean room ceilings have a less costly, more convenient, simpler, and more effective design. Sealant gels are no longer necessary. Individual filter units are self-supporting, freely of shared support with other filters requiring disturbance of adjacent filters when installing or deinstalling a single filter unit. The invention does away with the entire grid structure formerly though necessary both to support and to seal the clean room ceiling filter units against sideflows of unfiltered air. All the filters are in a plane and none need be vertically staggered as in the Gustin patent. No filter shares its final support with an adjacent filter, much less three adjacent filters as in the Madl patent. In this invention the filter units themselves carry externally their means of own individual support, eliminating the extensive grids used heretofore, and obviating the need for arbitrary spacing between adjacent filter units now left to accommodate the filter support grid. The filter units are readily shiftable into or out of position. Adjacent filter units are closer together than in conventional clean room ceilings, increasing the proportion of the ceiling that is composed of filter units, reducing air flow incursions between the filter units, its turbulence and concomitant vibration. The invention filter units and filter unit suspension assemblies cooperate to permit ready locking in place by simply shifting the filter unit into position with the fastening pin registering with the suspension support, and locking the filter to the support, from below, and without extensive screwing of threaded elements together. Conversely, the filter unit suspension assembly is simply disconnected, and from below the filter unit, for easy removal by reversing the installation process.
The filter units are sealed to each other across their narrow separation. Sideflows of air along the filter units walls are blocked by an adherent, suitably self-supporting mass or web bridging the gap between adjacent filters and lying across any possible flow path, an expedient made feasible by the close spacing of the filter units. The new filter support system is easily integrated
Braman Richard
Jeanseau Peter
Bachand Louis J.
Bushey C. Scott
HEPA Corporation
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