Patent Application
20070093196
1. Field of the Invention
The present invention generally relates to a housing assembly having an integrated damper, and more specifically, a housing assembly for an air filter having an integrated damper with a linear drive mechanism.
2. Description of the Related Art
Cleanrooms are utilized in many industries for contamination control and to improve product yields. A plurality of filters, typically mounted in the ceiling of the cleanroom, are configured to remove particulate from air entering the cleanroom at a predetermined efficiency selected based upon the cleanliness requirements of the activities performed in the cleanroom. As particulates load the filtration media disposed in the filter, the airflow through the filter decreases as the pressure drop across the filter increases. Once the filter reaches a critical pressure drop, the filter is typically replaced.
On other applications, replacement of filters is scheduled based on time or processes performed within the cleanroom. For example, in many pharmaceutical and biotech cleanrooms, periodic replacement of filters is required to meet regulatory or owner specifications. To facilitate efficient replacement of the filter, a hood (housing) is typically mounted in the cleanroom ceiling in which the filter may be readily removed and replaced.
Ducted supply hoods with roomside replaceable filters are commonly used in pharmaceutical applications for cleaning supply air to cleanroom manufacturing and process areas, as well as to laboratory areas. Most of these hoods are supplied with adjustable dampers that allow customers to regulate the airflow without having to remove the filter from the hood. The most common types of dampers are guillotine, opposed blade and butterfly types. When completely closed, these dampers essentially stop the flow of air to the hood. In many cases, the leakage through a closed damper is negligible in terms of flow rate, but is significant when considered in the terms of contamination of a cleanroom.
Because these types of dampers do not provide a seal (i.e., are not leak-free or bubble-tight), they are inadequate when it comes to decontamination processes that require complete isolation of the cleanroom. For example, during routine testing and validation of filters installed in a pharmaceutical facility, one or more filters may be found damaged, leaking and/or requiring replacement. When a technician removes that filter from the hood, the “seal” between the cleanroom and the contaminated plenum and supply ducts upstream of the removed filter is broken. When the new filter is installed, the “seal” between those two areas is restored, but the cleanroom has already been contaminated by air and particulate entering the cleanroom from the contaminated area of the plenum and supply ducts. Thus, the facility owner must perform a decontamination process of the entire room before resuming cleanroom operations. This is a very time-consuming and costly process.
Therefore, there is a need for a filter housing assembly having improved sealing capabilities.
Embodiments of the invention generally include a housing assembly having an integrated damper with a linear drive mechanism. In one embodiment, a housing assembly includes a housing having an inlet and an outlet. A damper is disposed in the housing and is positionable to regulate flow entering the housing through the inlet. A linear drive mechanism is operably coupled to the damper and is adapted to linearly move the damper between positions that are spaced-apart from the housing and a position that closes the inlet. The linear drive mechanism is configured to move the damper linearly without rotating the damper.
In another embodiment, a housing assembly includes a housing having an inlet and outlet. A damper is disposed in the housing and is linearly movable between positions that open and close the inlet. The damper has a non-planar shape that extends into the inlet when the damper is in a closed position. A means is provided for restraining the damper from rotating.
In another embodiment, a housing assembly includes an inlet port, an outlet port and a bag in/bag out filter access port. A filter receiving mechanism is disposed in the housing and is configured to direct gases flowing between the inlet and outlet ports through a filter installed in the housing. A first damper is disposed in the housing and is movable between positions that open and close the inlet port. A second damper is also disposed in the housing and is movable between positions that open and close the outlet port. A mechanism is provided in the housing that is configured to move the first damper between the open and closed positions without rotating the first damper, wherein the first damper is spaced apart from the housing when in the open position.
The teachings of the present invention can be readily understood by considering the following detailed description in conjunction with the accompanying drawings, in which:
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation.
It is to be noted, however, that the appended drawings illustrate only exemplary embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
Selected Embodiments of the Apparatus
The housing assembly 100 generally includes a housing 102 having an inlet 104 and an outlet 106. The inlet 104 and the outlet 106 are formed through the housing 102 and allow gases flowing through a duct 110, shown in phantom, to be routed through the housing 102. The inlet 104 is bounded by a collar 112 to facilitate coupling the duct 110 to the housing 102. A filter element 108 is disposed in the outlet 106 and is sealingly coupled to the housing 102 in a manner that causes gases flowing between the inlet 104 and the outlet 106 to pass through the filter element 108. The filter element 108 may be retained in the housing 102 in any suitable manner, for example by a clip 120 or fastener.
In the embodiment depicted in
The damper assembly 130 is disposed in the housing 102 between the inlet 104 and the filter element 108. The damper assembly 130 generally includes a damper dish 132, a linear drive mechanism 136 and a bracket 144. The bracket 144 is coupled to the housing 102. The bracket 144 generally supports and positions the dish 132 and linear drive mechanism 136 within the housing 102. The linear drive mechanism 136 is configured to move the dish 132 linearly to open and close the inlet 104.
Referring back to
In the embodiment depicted in
The rack 138 is slidably mounted through a set of bushings 142 that are coupled to the bracket 144. The bushings 142 may be comprised of any suitable bearing material, such as DELRIN® or brass. The bushings 142 may alternatively be roller bearings. The rack 138 may be exchanged to provide longer or short actuation strokes which correspondingly sets the orifice area between the dish 132 and the inlet 104.
In the embodiment depicted in
The dish 132 generally includes a conical face 160 having a sealing section 164 located adjacent a perimeter 166 of the dish 132. The sealing section 164 is adapted to engage the housing 102 and/or the collar 112 in a manner that facilitates sealing the air flow through the inlet 104. In the embodiment depicted in
A bearing 206 is press-fit into the bushing 202 and engages the shaft 152 to facilitate rotation. A seal 208 is disposed in one end of the bushing 202 to prevent air leakage between the bushing 202 and the shaft 152. The seal 208 may be an o-ring, cup seal, gasket, fluid seal or other seal suitable for preventing leakage of gas around the shaft 152 and through the hole 204 of the housing 102.
The shaft 152 includes terminal end 250 disposed outside the housing assembly 100. The terminal end 250 generally includes a drive feature 252 that facilitates inducing rotational motion to the shaft 152. In one embodiment, the drive feature 252 is a flat formed in the sides of the shaft 152. Other suitable drive features include, but are not limited to, hex heads, knurled surface, key ways, slots and the like. Although the terminal end 250 is shown extending from the side of the housing 102, it is contemplated that the drive feature 252 may be accessible from the other locations, such as from the outlet-side of the housing 100.
Referring to
In operation, the shaft 152 is selectively rotated to rotate the pinion gear 140. The rotating pinion gear 140 advances the rack 138, thereby linearly moving the dish 132. As the motion of the dish 132 is substantially perpendicular to the plane of the opening defined by the inlet 104, the seal 170 uniformly engages the lip 172, thereby enhancing seal uniformity and performance. Moreover, as the dish 132 is maintained centered relative to the flow entering (or exiting) the housing 102 through the inlet 104, the flow orifice defined between the dish 132 and lip 172 is uniform, thus, promoting flow uniformity through the filter element 108. The dish 132 is illustratively shown in a position closing and spaced from the inlet 104 in
In one embodiment, the housing assembly 600 includes a housing 602 having an inlet 604, an outlet 606 and at least one access port 608. The inlet 604 and outlet 606 are formed through the housing 602 and arrange to direct gases flowing through the housing 602. The access port 608 is configured to permit access to the interior of the housing 602, for example, for filter change-out, scanning a filter disposed in an adjacently coupled housing, and the like.
The housing 602 may be fabricated from a metal, such as aluminum, steel and stainless steel, or other suitable material. The housing 602 has a construction that forms a pressure barrier between gases flowing therethrough and an environment outside the housing 602. In the embodiment depicted in
The housing 602 additionally includes sealing flange 614 that sealingly engages a filter element 616 disposed in the housing assembly 600. A linkage mechanism 620 is provided in the housing 602 and is configured to move the filter element 616 between a position sealingly engaged with the flange 614 and a position clear of the flange 614. A seal, not shown, like the seal 170 described above, is disposed between the filter element 616 and flange 164 to prevent flow from bypassing the filter element 616.
The access port 608 is configured to facilitate removal of the filter element 616 from the housing 602 and is selectively sealed by a door 622. The access port 608 is circumscribed by a bagging ring (not shown) that is utilized to access the interior of the housing and/or remove and replace the filter element 616.
At least one end of the contamination housing 600 includes a linear damper assembly 130. The linear damper assembly 130 is as described above. In the embodiment depicted in
Life Cycle Testing
A housing assembly having an integrated linear damper assembly as described above was tested to determine if any significant or adverse amount of wear will occur between the fabricated pinion gear and rack (both fabricated from stainless steel); and if any significant or adverse amount of wear will occur in the bronze bushings used to support the rack and the damper shaft.
A one-high by one-wide containment housing was modified to accept the integrated linear damper assembly. The integrated damper assembly utilized a 12″ diameter stainless steel dish. A medium durometer silicone sponge gasket was cut by hand using a template. RTV was placed in the bottom of the channel of the dish. The gasket was seated in the channel, using the RTV as an adhesive to hold the gasket in the channel. The edges of the sponge gasket were not sealed in the channel, in order to test the seal with minimum adhesion to the dish.
The damper actuator included a three quarter inch diameter stainless steel shaft with keyway, which is typically used on conventional flat blade dampers. A pinion gear was fabricated from one quarter inch thick 304 stainless steel. Three gear pieces were stacked on top of each other with the keyways aligned and welded together to form a single gear about three quarter inch thick. The rack was manufactured from 20 mm diameter, 304 stainless steel shaft. The rack travels in a linear fashion and was held in place and aligned using bronze bushings coupled to the bracket. A bronze bushing was also installed in a support member to hold and align the damper shaft and assure proper meshing of the gear teeth with the rack.
A lip extending from a 12 inch (304.8 mm) diameter, 304 stainless steel collar circumscribing the inlet was used to form that knife-edge circumscribing the inlet. The collar was continuously welded to a piece of 11 gauge 304 stainless steel that was continuously welded to the upstream flange of the housing.
As an actuator coupled to the damper assembly rotated to turn the pinion gear, the rack is advanced linearly toward the inlet. The rack pushes the stainless steel dish toward the knife-edge mounted in the endplate of the housing. The silicone gasket around the perimeter of the dish sealed against the knife-edge. In one embodiment, the flat form of the teeth of the rack, engaged with the flat form of the teeth of the shaft substantially prevents rotation of the shaft.
Test Equipment & Instrumentation
The damper was bubble-tested in accordance with CFW-1000 CFW-10003, Revision 3: Pressure Decay/Structural Capability/Bubble Leak Testing. The containment housing with integrated damper was placed on a cart and a blank-off plate with ball valve and static pressure port was attached to the opposite end of the inlet collar that also serves as the knife-edge. This space was pressurized such that the damper was being pushed away from the knife-edge. The pressure was measured with a U-tube manometer that provided a differential pressure reading between the pressurized space and atmospheric pressure. Soap solution was sprayed on the interface between the knife-edge on the inlet ring and the silicone gasket that it was sealing against. Visual inspections were conducted for a period of 5 minutes to ensure bubble-tightness (i.e., a leak free condition).
Generally, bubble-tight dampers are bubble-leak tested at >+10″ water gauge (w.g.) (2.50 kPa). In some circumstances, they are required to be bubble-tight at >+15″ w.g. (3.74 kPa). During this test, the linear damper was tested at >+18″ w.g. (4.48 kPa).
After the initial bubble-test, power and compressed air were supplied to the actuator, and the damper was cycled between open and closed positions. Bubble-tests were conducted after more than 5,000, 10,000 and 15,000 cycles using the method described above. Visual observations were conducted throughout the entire test to determine the effect of rapid repeated cycling on the durability of the seal and actuation mechanism.
Results
The results of the cycle tests are as follows:
As shown in Table 1, the damper was bubble-tight at >+18″ w.g. (4.48 kPa) for each test conducted. It is believed that the damper would remain bubble-tight at higher pressures. The test was terminated after 15,260 cycles without failure to facilitate use of the lab for other projects. Upon visual observation and inspection of the mechanism for damper actuation after conclusion of the test, no evidence of mechanism wear, degradation or failure was apparent. There also was no visual evidence of gear wear.
The tested damper assembly compares favorably to conventional flat-blade dampers and dish-style dampers. The extended life is believed attributable to the design and construction of the damper assembly, which utilizes linear motion that has reduce bushing wear and stress compared to rotating blade. Moreover, the linear motion and the use of gearing reduces the power required to close the damper, thereby minimizing actuator costs.
The damper was proven to remain bubble-tight at >+18″ w.g. (4.48 kPa) at more than 15,000 cycles, which is 50 percent greater than the industry requirements (bubble-tight at +10″ w.g. (2.50 kPa) after 10,000 cycles). The robustness and durability of the mechanism are superior to both the flat-blade damper and dish-style damper designs, as proven by the lack of wear even after more than 15,000 cycles.
Although various embodiments which incorporate the teachings of the present invention have been shown and described in detail herein, those skilled in the art can readily devise many other varied embodiment that still incorporate these teachings.
This application claims benefit from U.S. Provisional Patent Application Ser. No. 60/729,644, filed Oct. 24, 2005, which is incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 60729644 | Oct 2005 | US |
