U.S. patent number RE31,952 [Application Number 06/598,984] was granted by the patent office on 1985-07-23 for method and apparatus for the leak testing of filters.
This patent grant is currently assigned to Flanders Filters, Inc.. Invention is credited to Thomas T. Allan, David E. Wilcox.
United States Patent |
RE31,952 |
Wilcox , et al. |
July 23, 1985 |
Method and apparatus for the leak testing of filters
Abstract
A method and apparatus for the leak testing of one or more
filters, which requires minimum space, and which comprises a
housing adapted to sealably mount the filters .[.means.].
.Iadd.apparatus .Iaddend.for introducing DOP particles within the
housing and immediately upstream of each of the filters, and a
funnel-shaped member mounted in the housing upstream of each filter
and downstream of the point at which the DOP is introduced. The
member may be selectively positioned to assume an operative
position transverse to the airstream wherein it acts to condense
and mix the airstream and DOP and then disperse the mixture over
the full frontal area of the adjacent filter, or a non-operative
position wherein the member is substantially withdrawn from the
airstream. .[.Means.]. .Iadd.Apparatus .Iaddend.are also mounted
downstream of each filter for monitoring the airstream to detect
DOP particles, and thereby permit a determination as to whether any
of the particles are leaking through or around the filter.
Inventors: |
Wilcox; David E. (Atlantic
Beach, NC), Allan; Thomas T. (Washington, NC) |
Assignee: |
Flanders Filters, Inc.
(Washington, NC)
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Family
ID: |
26873063 |
Appl.
No.: |
06/598,984 |
Filed: |
April 11, 1984 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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017289 |
Mar 5, 1979 |
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Reissue of: |
177234 |
Aug 11, 1980 |
04324568 |
Apr 13, 1982 |
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Current U.S.
Class: |
73/40.7; 239/514;
73/863.43; 95/25; 95/287; 96/417 |
Current CPC
Class: |
B01D
46/0004 (20130101); G01M 3/20 (20130101); B01D
46/002 (20130101); B01D 2273/18 (20130101) |
Current International
Class: |
B01D
46/42 (20060101); B01D 46/10 (20060101); B01D
46/12 (20060101); G01M 3/20 (20060101); G01M
003/20 (); B01D 046/12 (); B01D 046/42 () |
Field of
Search: |
;55/18,97,262,270,418,482 ;73/28,38,40,40.7,432PS,863.43
;239/456,457,514 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Burchsted et al., Nuclear Air Cleaning Handbook, printed by Oak
Ridge National Lab., pp. 187-208, 1976..
|
Primary Examiner: Lacey; David L.
Attorney, Agent or Firm: Bell, Seltzer, Park &
Gibson
Parent Case Text
This is a continuation of application Ser. No. 017,289 filed Mar.
5, 1979, now abandoned.
Claims
That which is claimed is:
1. A method for testing for leakage of particles of predetermined
size through a bank of filters installed in a parallel arrangement
in a housing and which is characterized by the ability to
individually test the filters in the bank under balanced flow
conditions and so as to permit the immediate identification of a
leaking filter in the bank, and comprising the steps of
passing an airstream concurrently through all of the filters in the
bank, while dividing the airstream into isolated portions
immediately upstream of each filter such that each isolated portion
of the airstream passes through a single filter,
partially restricting and imparting turbulence to the flow
concurrently through all of the isolated portions and at a point
upstream of each filter, and so as to obtain turbulence throughout
substantially the full cross sectional area of each isolated
portion and a substantially balanced flow among the isolated
portions, and including pivoting a restriction member mounted
within each of said .[.separate channels.]. .Iadd.isolated portions
.Iaddend.from a non-operative position disposed in general
alignment with the sides of the channel to an operative position
disposed transversely across the channel, then
sequentially introducing particles of predetermined size within
each isolated portion of the airstream and upstream of the point at
which the flow is partially restricted and made turbulent, to
thereby result in the particles being mixed in the air, and while
maintaining a substantially unrestricted flow between the point of
particle introduction and the point at which the flow is partially
restricted and made turbulent, and
monitoring the airstream downstream of the bank of filters to
detect at least a portion of any particles in the airstream, such
that a determination may be made as to which if any of the filters
in the bank is leaking.
2. The method as defined in claim 1 wherein the step of partially
restricting the flow further includes condensing the flow into a
central location with respect to each of the associated
filters.
3. The method as defined in claim 2 comprising the further step of
substantially uniformly dispersing the flow through each isolated
portion and immediately downstream of the point at which it is
partially restricted and made turbulent, and so that the mixed air
and particles are substantially uniformly dispersed over the
frontal area of the associated filter.
4. The method as defined in claim 1 wherein the step of monitoring
the airstream comprises partially restricting all of the isolated
portions of the airstream immediately downstream of the associated
filters, and while imparting turbulence thereto.
5. The method as defined in claim 4 wherein the step of monitoring
the airstream further comprises withdrawing samples of each of the
isolated portions of the airstream after it has been partially
restricted and made turbulent downstream of the filters, and in a
sequence corresponding to the sequence for introducing particles
into the isolated portions.
6. An apparatus for filtering an airstream and having provisions
for testing for leakage of particles of predetermined size through
or around each of at least two filters mounted in series, and
characterized by minimum space requirements, and comprising
a housing defining an air passageway adapted to form a part of an
air duct system having an airstream passing therethrough,
means .[.for.]. sealably mounting first and second filters within
the housing in a spaced apart, serial arrangement and such that the
airstream passing through the housing passes serially through the
first and then the second filter,
means for selectively introducing particles of predetermined size
into the airstream within the housing and immediately upstream of
each filter,
first restriction means mounted upstream of the first filter and
downstream of the associated particle introducing means for
partially restricting the airstream and imparting turbulence
theereto, and then dispersing the airstream over the full frontal
area of the first filter,
second restriction means mounted upstream of the second filter and
downstream of the associated particle introducing means for
partially restricting the airstream and imparting turbulence
thereto, and then dispersing the airstream over the full frontal
area of the second filter,
.Iadd.first particle detecting .Iaddend.means mounted upstream of
the second filter and downstream of said second restriction means
for detecting at least a portion of any particles in the airstream
to thereby permit a determination as to whether any of the
particles are leaking through or around the first filter, and
.Iadd.second particle detecting .Iaddend.means mounted downstream
of the second filter for detecting at least a portion of any
particles in the airstream to thereby permit a determination as to
whether any of the particles are leaking through or around the
second filter,
whereby the second restriction means is adapted to mix the
airstream and leaking particles during testing of the first filter,
and to mix the airstream and the particles introduced immediately
upstream of the second filter during testing of the second
filter.
7. The apparatus as defined in claim 6 wherein each of said first
and second restriction means includes a restriction member
pivotally mounted within said housing for movement between a
non-operative position disposed in general alignment with the sides
of the housing and an operative position disposed transversely
across the housing.
8. The apparatus as defined in claim 7 .Iadd..[.wherein said
particle detecting means mounted downstream of the second filter
comprises.]. .Iaddend..Iadd.further comprising .Iaddend.a third
restriction member pivotally mounted within said housing .Iadd.at a
location downstream of the second filter and upstream of said
second particle detecting means, with said third restriction member
being pivotally mounted .Iaddend.for movement between a
non-operative position disposed in general alignment with the sides
of the housing and an operative position disposed transversely
across the housing, and .Iadd.wherein said second particle
detecting means comprises .Iaddend.means positioned immediately
downstream of said third restriction member for withdrawing a
sample of the airstream to permit an analysis of the same.
9. The apparatus as defined in claim 8 wherein each of said means
for introducing particles into the airstream comprises a tubular
member extending transversely across said housing, said tubular
member having an opening therein which is disposed within said
housing, and means operable from outside the housing for
selectively introducing particles into said housing through said
opening.
10. The apparatus as defined in claim 8 or 9 wherein said
.Iadd.first .Iaddend.particle detecting means .[.mounted upstream
of the second filter.]. comprises means positioned immediately
downstream of said second restriction member for withdrawing a
sample of the airstream to permit an analysis of the same.
11. An apparatus for filtering an airstream through a bank of
filters and having provision for testing for leakage of particles
of predetermined size through or around any of the filters and
characterized by substantially balanced flow among the filters and
by the ability to permit the immediate identification of a leaking
filter in the bank, and comprising
a housing adapted to form a part of an air duct system having an
airstream passing therethrough,
means .[.for.]. sealably mounting a bank of filters in parallel
arrangement in said housing such that the airstream passing through
the housing passes through the bank of filters,
panel means mounted within said housing and immediately upstream of
the bank of filters for dividing the housing into a separate air
channel for each of the filters, and such that the airstream is
divided into an isolated portion within each of the separate
channels which passes through a single filter,
means mounted within each of said separate channels for selectively
introducing particles of predetermined size into the portion of the
airstream passing therethrough,
means mounted within each of said separate channels and upstream of
the filter and downstream of the particle introducing means for
selectively partially restricting and imparting turbulence to the
flow concurrently through all of the isolated portions, and so as
to obtain turbulence throughout substantially the full cross
sectional area of each isolated portion and thereby mix the
airstream and particles, and also achieve a substantially balanced
flow among the isolated portions, said restricting means including
a restriction member pivotally mounted within each channel for
movement between a non-operative position wherein at least a
substantial portion of the member is disposed parallel to the sides
of the channel, and an operative position disposed transversely
across the channel, said air channel for each of said filters being
free of any substantial restriction to flow between the particle
introducing means and said restriction member, and
means mounted within said housing and downstream of said filter
bank for detecting at least a portion of any particles in the
airstream to thereby permit a determination as to whether any of
the particles are leaking through or around any of the filters in
the filter bank.
12. The apparatus as defined in claim 11 .[.wherein said detecting
means comprises.]. .Iadd.further comprising .Iaddend.means
positioned immediately downstream of each filter for selectively
imparting turbulence to the portion of the airstream passing
therethrough, and .Iadd.wherein said detecting means comprises
.Iaddend.means for withdrawing a sample of the airstream downstream
thereof to permit an analysis of the same. .Iadd.
13. An apparatus for filtering an airstream and having provision
for testing for leakage of particles of predetermined size through
or around each of at least two filters mounted in series, and
characterized by minimum space requirements, and comprising
a housing defining an air passageway adapted to form a part of an
air duct system having an airstream passing therethrough,
means sealably mounting first and second filters within the housing
in a spaced apart, serial arrangement and such that the airstream
passing through the housing passes serially through the first and
then the second filter,
means for selectively introducing particles of predetermined size
into said housing at a first location which is upstream of said
first filter,
turbulence imparting means mounted downstream of said first filter
and upstream of said second filter for selectively imparting
turbulence throughout substantially the entire cross section of
said airstream,
means for selectively introducing particles of predetermined size
into said housing at a second location which is downstream of said
first filter and upstream of said second filter and such that the
introduced particles are subjected to the turbulence imparted by
said turbulence imparting means,
first particle detection means mounted upstream of the second
filter and downstream of said turbulence imparting means for
detecting at least a portion of any of said particles in the
airstream to thereby permit a determination as to whether any of
said particles which are introduced at said first location are
leaking through or around the first filter, and
second particle detection means mounted downstream of the second
filter for detecting at least a portion of any of said particles in
the airstream to thereby permit a determination as to whether any
of said particles which are introduced at said second location are
leaking through or around the second filter,
whereby said turbulence imparting means is adapted to provide the
separate functions of mixing the airstream and any leaking
particles during testing of the first filter, and mixing the
airstream and the particles introduced at said second location
during testing of the second filter. .Iaddend. .Iadd.
14. The apparatus as defined in claim 13 further comprising third
particle detection means mounted downstream of said first particle
introduction location and upstream of said first filter for
monitoring the concentration of the particles introduced at said
first location. .Iaddend. .Iadd.15. The apparatus as defined in
claim 14 further comprising second turbulence imparting means
mounted downstream of said second filter and upstream of said
second particle detection means for selectively imparting
turbulence throughout substantially the entire cross section of
said airstream. .Iaddend. .Iadd.16. The apparatus as defined in
claim 15 further comprising third turbulence imparting means
mounted downstream of said first particle introduction location and
upstream of said third particle detection means for selectively
imparting turbulence throughout substantially the entire cross
section of said airstream.
.Iaddend. .Iadd.17. The apparatus as defined in claim 16 wherein
each of said first, second, and third turbulence imparting means
comprises a restriction member pivotally mounted within said
housing for movement between a non-operative position disposed in
general alignment with the sides of the housing and an operative
position disposed transversely across the housing. .Iaddend.
.Iadd.18. The apparatus as defined in claim 14 wherein each of said
first, second, and third particle detection means comprises duct
means for withdrawing a sample of the airstream to permit an
analysis of the same. .Iaddend.
Description
The present invention relates to a housing for mounting one or more
banks of high efficiency air filters in an air duct system, and
which requires minimum space, permits the leak testing of the
filters from outside the housing, and which permits the
identification of a leaking filter in the bank.
In the manufacture of high efficiency air filtration systems, the
filters, housings, and related components are usually initially
tested as the final manufacturing step at the factory to locate any
leaks and insure compliance with the desired efficiency rating. In
addition, it is recognized that in-place testing of the completed
installation is essential to insure leak tightness of the housing
and filters in their assembled form. Also, in-place tests are
usually conducted after each change of a filter in the system to
insure proper installation of the new filter, as well as at regular
intervals after installation to detect any deterioration of the
gaskets or clamping devices, or the development of weld cracks or
the like in the housing which result in leaks. Such periodic
in-place testing is particularly important where harmful materials,
such as potentially radioactive substances, dangerous viable
organisms, or carcinogenic or toxic materials, are removed from the
airstream by the filtration system.
Both factory and in-place efficiency testing of filters and filter
installations conventionally utilizes either a monodispersed or a
polydispersed aerosol of dioctyl phthalate (DOP) droplets or
particles which have a light-scattering mean diameter of 0.3 to 0.7
microns, respectively. The DOP is introduced into the airstream at
a point in the duct far enough upstream of the filter or filter
bank to assure complete dispersion by the time it reaches the
filter or bank of filters. An upstream sampling device is usually
provided immediately upstream of the filter to determine the
concentration of the DOP in the duct, and a downstream sampling
device is provided to detect leakage. A portion of the airstream is
withdrawn from the duct through the sampling devices and conveyed
to an external photometric light-scattering instrument or the like
which is designed to determine the DOP concentration in both the
upstream and downstream samples.
In order to insure that the air-DOP mixture charged to the filters
is thoroughly mixed to obtain a substantially uniform dispersion,
and that the upstream sample is representative of the DOP
concentration at that point, it has been recommended that the DOP
be introduced at least ten duct diameters upstream of the filters,
or introduced upstream of baffles or turning vanes in the duct.
Also, the use of a Stairmand disk positioned three to five duct
diameters upstream of the filters has been recommended for this
purpose, see for example Chapter 7 of "Design, Construction, and
Testing of High Efficiency Air Filtration Systems for Nuclear
Applications" By Burchsted and Fuller, published January 1970 by
Oak Ridge National Laboratory. Thus in order to properly introduce
the DOP into the airstream utilizing these recommended procedures,
extra equipment and a great deal of space is required.
It is also presently recommended that the downstream sampling port
be located a considerable distance downstream of the filter, and
preferably downstream of the exhaust fan, to insure that any DOP
which leaks through the filter becomes sufficiently mixed with the
filtered air so that the leak will be detected no matter where in
the airstream the sample is withdrawn. This procedure not only
serves to further increase the space requirements of the test
apparatus, but also, it reduces the assurance that a leak will be
detected by reason of the dilution effect of the leaking DOP in the
great volume of filtered air. As will be apparent, this dilution
effect is particularly pronounced where a large bank of filters is
employed.
In installations requiring multiple banks of filters employed in
series, the space requirements for introducing the DOP, and
withdrawing the samples, are multiplied since the banks must be
separated a distance sufficient to accomplish the above objectives.
In an attempt to alleviate this problem, it has been proposed to
employ temporary ducts between the various banks with suitable
valves therein, and with the temporary ducts serving to selectively
isolate each bank in the apparatus during the test procedure and
introduce the DOP and withdraw the samples at an appropriate
distance from each bank. However, this proposed system is not
entirely satisfactory since it requires a great deal of extra
equipment which is only used during the test procedure, and the use
of temporary ducts adds additional problems of possible leakage
through the various required connections and valves.
Where the above tests indicate the presence of an unacceptable
leak, it is standard practice for a workman to physically enter the
duct at the downstream side of the filter bank to conduct leak
probing of individual filters, and thereby permit identification
and replacement of the faulty filter. In some cases, it is also
necessary for the workman to enter the upstream side to locate the
source of the leakage problem. Such direct personnel access is
often impractical and/or dangerous however, either because of the
system configuration, or because of high radioactivity levels or
the presence of other dangerous materials in the airstream. In such
cases, it has been previously proposed that the housing incorporate
remotely operated longhandles probes which are able to cover the
entire downstream area of the filter bank, or alternatively, that
the workman don protective clothing prior to entering the duct. As
will be apparent, neither of these alternatives is satisfactory,
since the design and fabrication of suitable remotely operated
probes significantly adds to the cost of the housing, and the
physical entry of a workman into the duct greatly increases the
risk of contamination to himself as well as other workers.
Still another problem associated with the above described
conventional testing procedure for a bank of filters is the fact
that a great deal of DOP must be fed into the airstream to assure
an adequate dispersion in front of each filter. Since the area of
the bank may be quite extensive, it is often difficult to achieve
an even distribution of the DOP over the face of the entire bank,
even when the DOP is introduced ten duct diameters upstream as
recommended, and in addition, it is difficult to generate a
sufficient quantity of the DOP for such large banks. Also, the DOP
tends to become deposited on all of the filters while each
individual filter in the system is being probed, thereby unduly
loading the filters and increasing their resistance to the passage
of the air.
Applicants' prior U.S. Pat. No. 4,055,075 discloses a method and
apparatus for the leak testing of filters wherein the above noted
disadvantages of the earlier techniques and equipment are
effectively overcome. More particularly, the applicants' prior
patent discloses a test housing wherein the DOP is introduced and
dispersed into the duct at a location closely adjacent the upstream
face of the filter to thereby minimize floor space, and wherein
each filter is charged with DOP and tested individually to permit
the ready identification of a leaking filter without manually
entering the duct and probing the filters. Further, in one
embodiment of the patented housing, there is provision for
selectively condensing and imparting turbulence to the airstream
immediately downstream of the filter so that the sample may be
withdrawn at a location immediately downstream of the filter to
thereby further reduce the space requirements.
The present invention relates to an improvement of the method and
apparatus as disclosed in the above prior patent. More
particularly, it has been found that the transition, plenum
connections, flanges, and other duct components located upstream of
the housing, can unless carefully designed, result in non-uniform
flow among the several filters in the bank, as well as non-uniform
flow to various portions of a single filter. This non-uniform flow
in turn renders it difficult to uniformly disperse the DOP to the
filters during the test procedure.
It is accordingly an object of the present invention to provide a
method and apparatus for the leak testing of filters, and which
includes a structurally simple, yet highly efficient means for
effectively dispersing an air-DOP mixture immediately upstream of
each filter.
It is another object of the present invention to provide a method
and apparatus for substantially uniformly balancing the air flow
among the several filters in a filter bank, to thereby facilitate
the uniform dispersion of DOP to each of the filters during a leak
testing procedure.
It is still another object of the present invention to provide a
method and apparatus for the leak testing of filters in series, and
wherein there is provided a single structure which is able to
selectively function to mix and condense the air passing through an
upstream filter to thereby permit a representative sample to be
readily withdrawn and analyzed during testing of the upstream
filter, or to mix and disperse the particles in the airstream
during the testing of a downstream filter.
It is also an object of the present invention to provide a
structure of the described type which may be selectively moved into
an operative position transverse to the airstream during a test
procedure, and then moved to a withdrawn position so as to provide
little interference with the normal air flow through the
housing.
These and other objects and advantages of the present invention are
achieved in the embodiments illustrated herein by the provision of
an apparatus which comprises a housing defining an air passageway
therethrough, means for sealably mounting a filter within the
housing, means for introducing particles of predetermined size into
the airstream, and means mounted at a point upstream of the filter
and downstream of the point at which the particles are introduced
for selectively partially restricting the airstream and imparing
turbulence thereto, and then dispersing the airstream over the full
frontal area of the filter. Preferably, the restriction means
comprises a funnel-shaped member mounted within the housing and
having a base with a peripheral outline closely corresponding in
size and configuration to the outline of the air passageway and an
apex having an opening therethrough. The funnel-shaped member is
movable between an operative position wherein the member is
disposed transversely across the housing and the airstream is
thereby condensed and passes through the opening in the
funnel-shaped member, and a non-operative position wherein at least
a substantial portion of the member is disposed along the side of
the housing and is substantially withdrawn from interference with
the airstream. Means are also provided for detecting at least a
portion of any particles in the airstream at a location downstream
of the filter to thereby permit a determination as to whether any
of the particles are leaking through or around the filter.
In the preferred embodiment, the housing is rectangular in
cross-section, and the funnel-shaped member is in the form of a
truncated four sided pyramid, and further comprises a tube affixed
about the periphery of the opening and extending in a direction
toward and perpendicular to the base of the pyramid. Also, the base
of the pyramid is preferably disposed downstream of the apex
thereof, so that the member acts to condense the airstream while
imparting turbulence thereto, and the airstream exiting from the
tube expands so that the airstream and particles are substantially
uniformly dispersed over the full frontal area of the adjacent,
downstream filter.
Where the housing mounts a bank of filters in parallel, the
invention further contemplates the positioning of panels upstream
of the filters to divide the housing into separate channels for the
filters, and a funnel-shaped member as described above is mounted
immediately upstream of each filter within each of the channels.
The filters may then be individually tested by initially moving
each of the funnel-shaped members to their transverse operative
position, sequentially introducing DOP into each air channel
upstream of the filter, and monitoring the airstream downstream of
the filter bank to detect for the presence of leaking DOP. By this
procedure, the funnel-shaped members function to partially restrict
the flow through each of the channels, resulting in a substantially
balanced flow among the isolated portions. This in turn facilitates
the uniform dispersion of the DOP within each channel.
Where the housing mounts a number of filters in series, a
funnel-shaped member as described above may be mounted intermediate
the filters, where it functions to mix and condense the air passing
through the upstream filter during testing thereof to permit a
representative sample to be readily withdrawn and analyzed, and to
mix and disperse the particles in the airstream during the testing
of the downstream filter.
Some of the objects having been stated, other objects will appear
as the description proceeds, when taken in conjunction with the
accompanying drawings in which
FIG. 1 is a perspective view of a filter test housing which
embodies the features of the present invention;
FIG. 2 is a perspective view, partly broken away, of the upper half
of the filter housing shown in FIG. 1;
FIG. 3 is a sectional elevation view taken substantially along the
line 3--3 of FIG. 2, but with the final funnel-shaped member being
shown in its non-operative position;
FIG. 4 is a fragmentary perspective view illustrating the apparatus
for restricting and disturbing an airstream in accordance with the
present invention;
FIG. 5 is a front elevation view, on a reduced scale, of the
upstream side of the apparatus shown in FIG. 2;
FIG. 6 is a fragmentary elevation view, illustrating the DOP
sampling device and taken substantially along the line 6--6 of FIG.
3;
FIG. 7 is a sectional plan view of the upstream portion of the
apparatus shown in FIG. 3, but illustrating only one of the air
channels; and
FIG. 8 is a perspective view of the funnel-shaped member of the
present invention, and illustrated in its non-operative position in
the housing.
Referring more specifically to the drawings, one embodiment of the
present invention is illustrated which includes a housing 12 which
is adapted to form a part of an air duct system, such as an exhaust
air cleaning system in a nuclear fuel manufacturing facility. More
particularly, the housing 12 comprises a generally box-like
enclosed structure having two side walls 14 and 15, a top wall 16,
and a bottom wall 17. Also, the housing defines a forward open end
which is joined to an air inlet opening of the inlet duct 21 via
the transition member 22, and a rear open end which is similarly
joined to the outlet duct 24 via the transition member 25. The
housing is typically fabricated from a sheet metal material, such
as .[.14.]. .Iadd.fourteen .Iaddend.gauge stainless steel.
In the illustrated embodiment, the housing 12 mounts two banks of
filters in series, with each bank comprising four filters 30 in
parallel. Typically, each filter 30 is about 24.times.24.times.12
inches in size, and comprises a wooden or chipboard frame 31
surrounding and supporting a pleated filtering media 32, such as a
nonwoven fiberglass or cellulose-asbestos sheet material. Filters
of this type may have extremely high dust retention
characteristics, usually greater than about 95% efficiency, and
typically 99.97% efficiency, as measured by the conventional DOP
test, and are known as "absolute" or HEPA filters in the art.
The filters 30 of each bank are adapted to be inserted and removed
from the housing 12 through the two associated side access doors
34, 35 with the two upper filters in each bank being inserted and
removed through the upper door 34, and the two lower filters being
inserted and removed through the lower door 35. As is well known in
the art, clamping means as shown somewhat schematically in FIG. 7
at 29, and sealing means are provided in the housing 12 for
sealably mounting each of the filters therein. This sealing means
may include a resilient gasket on the front peripheral face of the
filter frame 31, or a fluid type seal such as shown schematically
at 33 and as described in the U.S. Pat. Re. 27,701 to Allan. Where
a dangerous substance, such as radioactive material or viable
organisms may be present on the filters or in the airstream, the
housing may further include a conventional "bag-out" ring (not
shown) about each of the access doors 34, 35 to permit the filters
30 to be enclosed in a plastic bag while being removed from the
housing and thereby avoid possible contamination.
The portion of the housing 12 immediately upstream of each bank of
filters is divided into four separate and rectangular air channels
by means of the four perpendicularly disposed panels 36, 37, 38 and
39. Each channel is aligned with one of the filters, and generally
conforms in cross-sectional outline and size to that of the
associated filters. Thus for example, the panels 36 and 37
cooperate with the side wall 14 and top wall 16 to define a
separate air channel upstream of the filter located in the upper
left hand corner of the bank as seen in FIG. 1. By this
arrangement, the airstream entering the housing from the transition
member 22 is divided by the panels into four equal portions, with
each portion being isolated from the other portions and directed to
pass through a single filter. Where the housing mounts a number of
banks of filters in series, the panels 36-39 may extend the entire
distance between the banks as best seen in FIG. 2 so as to
similarly define air channels for the downstream filters. In this
regard, it will be understood that the panels 36 and 38 are
discontinuous at points immediately adjacent the filters to
accommodate the sliding receipt of the inner filter, as well as the
clamping mechanism 29, note FIG. 7.
In accordance with the present invention, means are provided for
selectively introducing particles of predetermined size (typically
DOP particles having a mean diameter of between about 0.3 to 0.7
microns) in the portion of the airstream passing through each one
of the channels. As illustrated, this particle introducing means
comprises two pairs of supply pipes 40 and 41 which extend
horizontally through the housing upstream of the first bank of
filters. One pair of supply pipes is operatively associated with
the two upper filters in each bank, and another pair is operatively
associated with the two lower filters. As best seen in FIG. 5, the
pipe 40 terminates at a point centrally disposed in the adjacent
air channel, and the pipe 41 extends in a central location in the
far air channel. Both pipes include an exteriorly positioned cap
42, to permit the pipes to be selectively coupled to a DOP supply
source.
The apparatus of the present invention also includes means mounted
within each of the separate channels for selectively mixing the
airstream and DOP particles, and then substantially uniformly
dispersing the same over the full frontal area of the adjacent
filter. In the illustrated embodiment, this mixing and dispersing
means comprises restriction means in the form of a funnel-shaped
member 54 mounted upstream of the filter and downstream of the
associated DOP supply pipe. The funnel-shaped member 54 comprises a
truncated, four sided pyramid which includes a base 56 which has a
rectangular peripheral outline corresponding in size and
configuration to the cross-sectional outline of the interior of the
channel, and which defines a plane disposed transversely across the
channel. A flange 57 is affixed to the base 56 to facilitate the
mounting of the member in a rectangular duct. The member 54 also
has an apex having a rectangular opening 58 therethrough, and a
tube 59 having a rectangular cross-sectional outline corresponding
to that of the opening 58. The tube is affixed to the periphery of
the opening 58 and extends a substantial distance into the interior
of the member and in a direction parallel to the direction of air
flow, i.e., toward and perpendicular to the plane defined by the
base 56. Preferably, the tube extends at least about one-half the
distance to the plane of the base 56.
A transverse deflector 80 overlies in spaced relation the free end
of the tube 59, and as best seen in FIG. 7, the deflector acts to
laterally deflect the airstream moving through the tube, and
thereby achieve a substantially uniform dispersion to the
downstream filter. In the illustrated embodiment, the deflector 80
comprises a four sided pyramid which is disposed with its base
overlying the downstream end of the tube 59. The deflector is
attached to the tube by any suitable means, and as illustrated, the
attachment means comprises a longitudinally directed threaded
member 81 fixed to the inside of the deflector, and a cooperating
transverse strap 82 mounted across the opening of the apex of the
member 54. By this arrangement, longitudinal adjustment of the
deflector with respect to the tube is permitted so that the spacing
therebetween can be readily adjusted to best achieve the desired
uniform dispersion.
The funnel-shaped member 54 also is composed of two separate
components, namely, the lower base portion 61 which is adjacent the
base 56, and a separate apex portion 62 adjacent the apex and
including the tube 59 and deflector 80. The base portion 61 of the
member 54 is fixedly mounted in the channel of the housing by
welding or the like, and it may be described as being truncated to
define a relatively large rectangular opening (not numbered)
disposed centrally in the housing. The apex portion 62 is hingedly
mounted to the base portion by a hinge 63 which extends
transversely across the housing and adjacent the opening of the
base portion. In addition, the two portions 61, 62 including mating
flanges 64 to facilitate the interface thereof.
To more particularly describe the size and configuration of an
exemplary embodiment of the member 54, the base 56 and opening 58
are each square in cross-section, with the base being about 24
inches along each side and the opening 58 being about 6 inches
along each side. The flange 57 is about 1 inch wide, the
longitudinal distance from the base 56 to the apex is about 51/4
inches, and the tube 59 has a longitudinal length of about 3
inches.
The apex portion 62 may be pivoted between an operative position
wherein the member is in the form of a truncated pyramid which is
disposed transversely across the air passageway, and a
non-operative position (note the position of the member 54c in FIG.
3) wherein the apex portion 62 is disposed along the side of the
air passageway so as to be substantially withdrawn from
interference with the airstream. The means for operatively
controlling the positioning of the apex portion 62 of the member 54
comprises a control rod 65 which extends through the wall 14 of the
housing and in a direction parallel to the hinged interconnection
63. A linkage 66, 67 interconnects the rod 65 and apex portion 62
(note FIG. 4), and a crank 68 is positioned on the outside of the
housing for rotating the rod to pivot the apex portion 62 between
its operative and non-operative positions. In this regard, it will
be noted that the rod 65 extends through the two laterally adjacent
channels, such that the two members 54 are concurrently operated by
rotation of the rod.
Viewing FIG. 3, it will be seen that the housing includes a first
funnel-shaped member 54a positioned upstream of the first filter, a
second like funnel-shaped member 54b mounted immediately downstream
of the first filter and upstream of the second filter, and a third
like funnel-shaped member 54c which is mounted immediately
downstream of the second filter.
The housing 12 also includes means for withdrawing a sample of the
airstream at each of three separate locations along its length. A
first sampling means 70a is provided immediately downstream of the
first funnel-shaped member 54a, a second sampling means 70b
immediately downstream of the second member 54b, and a third
sampling means 70c immediately downstream of the third member 54c.
Each of these three sampling means comprises a first pipe 71
extending laterally into the first adjacent channel and having an
apertured sampler 72 positioned immediately downstream of and in
alignment with the tube 59 of the adjacent funnel-shaped member,
and a second pipe 73 extending into the laterally remote channel
and including a similarly positioned sampler 74, note FIG. 6. Each
pipe extends through the wall 14 of the housing, and includes a
removable end cap 75 for permitting the sampler to be selectively
connected to a conventional DOP detecting apparatus.
During normal operation of the filter housing 12, the apex portions
62 of all of the funnel-shaped members 54 are lowered into their
non-operative position, so as to minimize air resistance. When
leakage tests are to be conducted on the upstream bank, the apex
portions 62 of the four members 54a which are upstream of the
initial bank of filters, as well as the four members 54b
immediately downstream of this bank, are all raised into their
operative positions. The third members 54c preferably remain open,
such that the various members are oriented in the manner shown in
FIG. 3.
The above disposition of the members results in the air flow being
partially restricted as it moves through each of the four channels,
and this restriction produces a back pressure upstream of the
housing, which in turn serves to substantially balance the flow
among the four channels. Thus an uneven flow pattern resulting from
the design of the transition 22, plenum connections, or other
upstream duct components, is avoided.
The DOP particles are then selectively and independently introduced
into each of the four channels by means of their associated pipes
40 and 41. In each instance, the airstream and entrained particles
approach the first member 54a, and substantial turbulence is
imparted thereto to mix the particles and air as illustrated
schematically in the right hand portion of FIG. 3, and the
airstream is condensed into the tube 59 of the member. As the
airstream exits the tube 59 and deflector 80, it is dispersed over
the full cross-sectional area of the channel. At relatively low
flow rates, such as where testing is conducted for example at 20%
of the designed flow rate of the housing, substantially uniform
dispersion over the full frontal area of the filter is achieved.
The first sampling means 70a may at this point in the test be
connected to the DOP detecting apparatus to determine the upstream
concentration of the DOP.
The airstream continues through the first filter and strikes the
downstream second member 54b, which again imparts turbulence to the
airstream and condenses it to pass through the tube 59 of the
member. Thus the air and any leaking DOP is thoroughly mixed by the
time it passes through the tube 59, and such that the sampler 72
(or 74), which is positioned immediately downstream of the tube 59
will be assured of picking up a representative portion of any
leaking DOP when it is connected to the detecting apparatus. By
this testing procedure, each filter in the first bank may be
individually tested, so that the identification of a leaking filter
is readily apparent.
To test the filters of the second bank, the four members 54a are
preferably moved to their non-operative lowered position, and the
two downstream sets of members 54b and 54c are each moved to their
operative positions. DOP is then selectively introduced from the
associated pipes 40, 41 into each of the four channels, and samples
are withdrawn through the samplers of the third sampling means 70c
to detect any leaking DOP in the manner described above. In this
instance, it will be noted that the members 54b now serve the dual
functions of balancing the flow to the second bank of filters, and
mixing the air and DOP particles and dispersing the mixture to the
second filters. Thus a single component in the housing, namely the
members 54b, perform distinctly different functions during the
testing of the two filter banks.
In the drawings and specification, there has been set forth a
preferred embodiment of the invention, and although specific terms
are employed, they are used in a generic and descriptive sense only
and not for purposes of limitation.
* * * * *