Particulate filter assembly

A filter assembly for collecting particulate matter from a stream of sample gas. A filter housing having at least an inlet section and an outlet section supports one or more removable filter elements between adjacent housing sections. At least one end of each housing section is provided with a tapered flange whereby it may be joined to the end of an adjacent housing section. Quick-release clamping means engages the flanges to provide a convenient means for fastening and unfastening the sections of the filter housing without dislodging appreciable quantities of the particulate matter collected on the filter elements. The filter assembly may be expanded as required to accommodate any desired number of filter stages.

BACKGROUND OF THE INVENTION 
In measuring the particulate content of a sample gas stream such as, for 
example, the exhaust of a diesel engine, it has long been the practice to 
direct the sample stream through a filter assembly containing a removable 
filter element having suitable particle retention characteristics. Such 
filter assemblies have included two-section filter housings which have 
been fastened together by a threaded sleeve that is loosely attached to 
one housing section and that screws onto mating threads on the other 
housing section. Such filter assemblies have several shortcomings which 
make their use inconvenient and which can give rise to inaccurate 
measurements. 
One shortcoming is that the threaded fastener takes a relatively long time 
to disassemble and reassemble during the course of replacing a filter 
element. Another shortcoming of the above type of filter assembly is that 
the sustained vibration that is incident to the unscrewing of the threaded 
fastener can dislodge particulate matter from the filter element and 
thereby introduce errors into weight measurements made thereon. Still 
another disadvantage of the above type of filter assembly is the tendency 
of the threads to become stripped or clogged with particulate matter 
during the course of repeated openings and closings. Finally, threaded 
fastener type filter assemblies cannot be conveniently connected in 
series; multiple stage filter structures can be provided only by providing 
a multiplicity of complete filter assemblies, each independently connected 
to the tubing through which the sample is supplied. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, the above-described shortcomings 
are eliminated by providing a filter assembly having an improved fastening 
structure. In the preferred embodiment this structure includes a plurality 
of housing sections each having a tapered flange at at least one of the 
ends thereof and one or more quick-release clamps which engage respective 
pairs of tapered flanges to produce a mechanically strong, gas tight seal 
between the housing sections. By means of this fastening structure the 
user may, by a simple movement of the hand, release the clamp and thereby 
allow the housing sections to be separated for filter removal and 
replacement. In this manner there is avoided the more time consuming 
loosening and tightening of a threaded fastener and the associated 
dislodgement of particulate matter from the filter element within the 
housing. 
The fastening structure of the invention also allows the filter assembly to 
be easily and conveniently expanded or contracted to accommodate any 
desired number of serially disposed filter elements, each of which may be 
easily and conveniently inserted or removed without significantly 
disturbing the particulate matter deposited on any of the other filter 
elements. In the preferred embodiment of the invention, for example, the 
filter assembly is provided with a middle or intermediate section as well 
as an inlet section and an outlet section, each section being joined to 
the adjacent section in the manner contemplated by the present invention. 
This allows a filter element to be positioned between each pair of housing 
sections and thereby allows the efficacy of one filter element to be 
checked by another. A back-up filter element may, for example, be located 
downstream of the main filter element with the presence of particulate 
matter on the back-up filter element being used as an indication of the 
efficiency of the upstream filter element. In this manner the user can 
avoid the use of inaccurate data. 
In addition, in applications in which the size distribution of particulate 
matter is of significance, the present invention makes convenient the 
cascading of filter stages with filter elements of increasing fineness. 
This allows coarse particles to be collected on a first filter element, 
finer particles to be collected on a second filter element, and so on, 
through as many stages as is desired. Moreover, the present invention 
makes it easy to convert from one of these filter configurations to 
another without using any tools.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIG. 1, there is shown one embodiment of a particulate filter 
assembly of a type suitable for practicing the present invention. This 
filter assembly includes a generally tubular housing 12 including an inlet 
section 12a, an outlet section 12b and an intermediate or middle section 
12c. Inlet section 12a is provided with an inlet end 14 having an opening 
for receiving a particulate-bearing stream of sample gas and an outlet end 
16 adapted to be joined to housing section 12c at a junction 18. In order 
that this junction may be gas tight, a suitable O-ring 20 may be provided 
between housing sections 12a and 12c. 
Similarly, outlet section 12b is provided with an outlet end 22 having an 
opening for exhausting the sample stream to an exhaust vent or downstream 
instrument, and with an inlet end 24 which is adapted to be joined to 
middle section 12c at junction 26. As in the case of junction 18, junction 
26 may be rendered substantially gas tight by means of a suitable O-ring 
seal 28 positioned between housing sections 12b and 12c. It will be 
understood that junctions 18 and 26 prefereably lie in a plane or set of 
planes that is perpendicular to the axis of sample gas flow through the 
filter assembly. 
For the sake of clarity, the following terminology convention is adapted 
for use herein. The terms "inlet" and "upstream", when used as adjectives, 
refer to structures which are closer to the source of sample gas than 
structures described by the adjectives "outlet" or "downstream". Inlet end 
14 of housing section 12a may, for example, be said to be upstream of 
outlet end 22 of housing section 12b. Similarly, inlet section 12a may be 
said to have an inlet end for connection to a source of sample gas and an 
outlet end for connection to middle section 12c. Finally, housing section 
12a may be said to be an upstream housing section with respect to housing 
sections 12b and 12c, but middle housing section 12c may be said to be an 
upstream housing section only with respect to housing section 12b. 
To the end that inlet section 12a may be connected to a source of sample 
gas, inlet section 12a is provided with an inlet tube 30 which terminates 
in a suitable threaded female coupling 32 of a well known type. In the 
preferred embodiment inlet tube 30 is inserted into a hole in housing 
section 12a and is welded in place to provide a permanent, gas-tight 
connection. Tube 30 may, however, be formed integrally with housing 
section 12a, if desired. 
Similarly, outlet section 12b is provided with an outlet pipe 36 which 
terminates in a suitable threaded male coupling 38 of a well known type. 
Outlet pipe 36 is preferably a tube which is inserted into a hole in 
outlet section 12b and which is welded in place to provide a permanent, 
gas-tight seal. It may, however, be formed integrally with outlet section 
12b, if desired. 
While inlet pipe 30 and outlet pipe 36 are shown as having different 
diameters, this need not be the case. A larger diameter inlet tube may 
nevertheless be desirable in certain instances because of the effect that 
the diameter of the tube has on the ability of the sample stream to 
maintain particulate matter in a suspended state. Once this suspended 
matter is removed by the filter assembly, however, such considerations are 
no longer important and, as a result, outlet tube 36 may have any 
convenient diameter. 
To the end that the suspended particles entering the filter assembly may be 
trapped and retained therein, the filter assembly is provided with one or 
more replaceable filter elements 42 and 44 which may be of any desired 
type such as, for example, glass fiber filters. Such filter elements 
preferably have as small a weight as possible so that the particles 
trapped thereon may comprise the greatest possible percentage of the total 
weight of the filter element. This assures the lowest possible percentage 
error in weight measurements made on the removed filter elements after 
exposure to the sample stream. 
In order to prevent filter elements 42 and 44 from being deformed, each 
element is supported across substantially the entire surface area thereof 
by respective support elements 42a and 44a. Support elements 42a and 44a 
may, for example, consist of a perforated sheet metal or coarse screen 
disc having sufficient rigidity to maintain filter element 42 in a plane 
substantially perpendicular to the longitudinal axis 34 of the filter 
assembly. In applications in which it is objectionable for particulate 
matter to become concentrated immediately in front of the coarse 
perforations or openings in support element 42a, additional, finer grades 
of screen discs may be interposed between elements 42 and 42a in order to 
cause the trapped particulates to be spread more evenly over the surface 
of element 42. 
To the end that each filter element and its associated support element or 
elements, hereinafter referred to collectively as a filter element 
assembly, may be securely mounted within the filter assembly, each filter 
element assembly is held in place in the vicinity of one of the junctions 
of the filter housing by suitable mounting means which here take the form 
of recesses or shoulders in the ends of the housing sections. In FIG. 1, 
for example, intermediate section 12c is provided with a mounting recess 
46 at its inlet end, this recess having a depth sufficient to receive 
filter element assembly 42-42a and position filter element 42 against the 
outlet end of housing section 12a. In this way, when sections 12a and 12c 
are separated, filter element 42 is exposed for easy removal at junction 
plane 18. Similarly, the filter element assembly 44-44a is positioned 
within a mounting recess 50 in the inlet end of outlet section 12b so that 
filter element 44 may be securely mounted between housing sections 12b and 
12c. It will be understood that mounting recesses 46 and 50 may be deep 
enough to position the respective filter elements a short distance away 
from the respective junction plane, if suitable spacers are provided to 
hold the filter elements securely in place at that location. 
In order that housing sections 12a, 12b and 12c may be rapidly and 
conveniently separated without substantial disturbance to the particulate 
matter deposited on filter elements 42 and 44, housing sections 12a and 
12c are provided with mating tapered flanges 18a and 18b which are located 
on opposite sides of junction 18, and housing sections 12b and 12c are 
provided with mating tapered flanges 26a and 26b which are located on 
opposite sides of junction 26. In accordance with the present invention 
flanges 18a and 18b are forced together, along longitudinal axis 34, to 
form a substantially gas tight seal between housing section 12a and 12c by 
radially directed clamping forces produced by quick-release clamping means 
which here takes the form of an over center latch 54 that bridges junction 
18. Similarly, mating flanges 26a and 26b are forced together to provide a 
substantially gas tight seal between housing sections 12b and 12c by 
radially directed clamping forces produced by an over center latch 56 that 
bridges junction 26. 
As shown in FIGS. 1 and 1a, clamp 54 includes flat exterior band 54a, a 
grooved interior band 54b, a manually operable, pivotally mounted handle 
54c and a band terminating pin 54d. When handle 54c, which serves as a 
clamping control element, is in the position shown in FIGS. 1 and 1a, band 
54a is at its maximum tension and thereby produces its maximum inward 
(radial) force on grooved band 54b. Under this condition, tapered flanges 
18a and 18b are pressed tightly together to maintain the desired gas tight 
seal between housing section 12a and 12c. When, however, handle 54c is 
raised from the position shown, the tension on band 54a is released, 
thereby releasing the clamping force on flanges 18a and 18b. Under this 
condition, clamp 54 becomes loose enough so that it may be moved to one 
side of the junction. This, in turn, allows sections 12a and 12c to be 
pulled or slid far enough apart to allow the removal and replacement of 
filter 42, provided that the tubing connected to couplings 32 and 38 has 
sufficient flexibility to permit this motion. It will be understood that 
the clamping control handle of clamping means 56 operates between its two 
positions, in the manner described in connection with clamp 54, to clamp 
or release flanges 26a and 26b of housing sections 12b and 12c and thereby 
allow the removal and replacement of filter 44. Thus, each of the clamps 
54 and 56 is a two-state clamping element having a two-position control 
handle. 
While the clamps 54 and 56 will accomplish their purpose without regard to 
whether the clamping action thereof is continuous (without a snap-action 
characteristic) or has a two-state or latching characteristic, the 
preferred embodiment of the invention has such a two-state characteristic. 
It will be understood, however, that the snap-action is not so pronounced 
as to result in the dislodgement of collected particulate matter. The 
desired degree of snap-action may be selected, in the clamp illustrated in 
FIG. 1a, by means of an adjustment nut 54e. 
Because clamps 54 and 56 preferably comprise over-center latches of a known 
commercially available type, the operation thereof will not be described 
in detail herein. 
In view of the foregoing, it will be seen that if the user wishes to remove 
and replace either filter element, he need only lift the handle of the 
respective clamp, move the housing sections far enough apart to remove and 
replace the filter element, reposition the housing sections and lower the 
clamp handle. Thus, the present invention allows a filter element to be 
quickly and conveniently removed and replaced without any appreciable 
disturbance of the particulate matter deposited on the filter element 
during a sampling period. 
Even if the external tubing (not shown) to which the filter assembly is 
connected is not sufficiently flexible to allow filter elements 42 and 44 
to be individually removed and replaced in the manner described above, 
these elements may be serviced, without loosening threaded couplings 32 or 
38, by releasing both of handles 54c and 56c. This allows both clamps to 
be moved aside so that intermediate housing section 12c may be slid out 
from between housing sections 12a and 12b, thereby providing simultaneous 
access to filter elements 42 and 44. Thus, the use of two clamps allows 
one or both filter elements to be removed and replaced without the use of 
any threaded element and without any significant change in the 
longitudinal position of housing sections 12a and 12b. 
While, as shown in FIG. 1, the preferred embodiment of the invention 
includes three housing sections and two filter elements, the present 
invention is not limited to these numbers of housing sections and filter 
elements. Referring to FIG. 2, for example, there is shown a filter 
assembly having only two housing sections and one filter element, 
corresponding elements in FIGS. 1 and 2 being similarly numbered. The 
embodiment of FIG. 2 may in fact be easily derived from the embodiment of 
FIG. 1 by simply removing intermediate housing section 12c, filter element 
42 quick release clamp 54 from the embodiment of FIG. 1. This derivation 
may even be accomplished with the filter assembly connected in place, 
provided that the external tubing has sufficient flexibility or slack to 
allow the end sections of the filter housing to meet. In view of this 
simple, derivative relationship, the embodiment of FIG. 2 will not be 
described in detail herein. 
Conversely, the present invention has a structure which facilitates 
increasing the number of filter stages from two to three or even more. 
Such increases or expansions are accomplished by merely separating one of 
the end sections of housing 12, inserting an additional intermediate 
section such as 12c, and clamping the junctions of the expanded filter 
assembly with clamps such as 54 or 56. As was the case with reductions in 
the number of filter stages, this modification may be accomplished with 
the filter assembly connected in place if the external tubing has 
sufficient flexibility. One application in which such additional stages 
are desirable is one in which it is necessary for the sample gas stream to 
encounter a succession of successively finer filter elements which, in 
effect, sort the particulate matter according to size during the course of 
its passage through the filter assembly. Because the structure resulting 
from the insertion of such additional filter stages is so straightforward, 
no drawing showing an embodiment with such additional stages is included 
herein. 
In the embodiments of FIGS. 1 and 2 each filter element assembly is 
illustrated as being at the input or inlet end of the housing section in 
which it is mounted. This choice of location for the filter element 
assemblies is not a necessary one, however, as is shown in the embodiments 
shown in simplified cross-sectional form in FIGS. 3a-3c, 4 and 5. In all 
of these figures, corresponding elements are similarly numbered, numerical 
subscripts being added to the indicia used in later described figures to 
indicate elements which are similar but not identical to elements shown in 
earlier described figures. 
Referring to FIG. 3a, for example, there is shown an embodiment of the 
invention in which both filter element assemblies are positioned within 
respective recesses 46 and 50.sub.1 of intermediate housing section 
12c.sub.1. The advantage of the embodiment of FIG. 3a is that it allows 
intermediate section 12c.sub.1 to be removed, with the filter elements in 
place, and replaced with another intermediate section having clean 
replacement filter elements positioned thereon. The exposed filter 
elements from the removed housing section can then be removed at a remote 
location at which greater care may be exercised than may be possible at 
the site at which the filter assembly is used. 
FIG. 3b illustrates an embodiment of the invention in which the filter 
element assemblies are both located in recesses in respective end sections 
of the filter assembly. FIG. 3c illustrates still another embodiment in 
which the filter element assemblies 42-42a and 44-44a are located in 
recesses that are immediately upstream of junctions 18 and 26, 
respectively. These embodiments are included for the sake of completeness 
and to illustrate the fact that the filter element assemblies of the 
invention need only be located in the general vicinity of the respective 
housing section junctions. 
In the embodiments shown in FIGS. 1 through 3c, the filter element 
assemblies and recesses have each been proportioned and positioned so that 
one side of each filter element assembly is at or close to the respective 
housing section junction. While these embodiments are desirable in many 
applications, they may not be desirable in all circumstances. In 
applications in which relatively thick accumulations of particulate matter 
are expected to collect on the filter elements, for example, the sliding 
movement of one housing section past another may result in the scraping 
off of accumulated particulate matter. An embodiment of the invention in 
which this problem is eliminated is illustrated in FIG. 4. 
Referring to FIG. 4, there is shown a simplified cross-sectional view of an 
embodiment of the invention in which the filter element assemblies are 
recessed relatively deeply within the housing sections in which they are 
mounted. In order to securely hold a filter element assembly between 
adjacent housing sections in such embodiments, the housing section on one 
side of a junction may be provided with a pilot projection or surface that 
fits into the housing section on the opposite side of the junction. In 
FIG. 4, for example, male pilot projections such as 60 and 62 may be 
provided to facilitate the orienting of adjacent housing sections prior to 
clamping as well as to retain filter elements 42 and 44 within recesses 46 
and 50, respectively. 
In the presence of pilot projections 60 and 62, it is apparent that as the 
housing sections are separated during filter removal and replacement, the 
initial separating movement must occur in the longitudinal direction. This 
is a desirable result since limiting the initial movement of the housing 
sections to this direction prevents the moving housing sections from 
scraping across the surface of the filter elements. Thus, projections such 
as 60 and 62 serve a movement limiting function as well as the previously 
mentioned orienting and retaining functions. 
It will be understood that the embodiment of FIG. 4 may be implemented with 
projections 60 and 62 located on either side of either housing junction, 
but these additional embodiments are not shown herein for the sake of 
brevity. It will also be understood that the advantages of these 
projections may also be provided in the embodiments of FIGS. 1 through 3, 
since there is no necessity that the pilot projections fit into the 
mounting recesses. They may, for example, take the form of concentric 
projecting rings or even piloting pins, provided that the surfaces of the 
mating housing sections are configured to receive them. 
The only disadvantage of the embodiment of FIG. 4 is that the filter 
elements are located in recesses at some distance from the respective 
junction. As a result, the removal of a filter element by, for example, 
prying into the recess with the point of a knife, can result in the 
shaking off of particulate matter deposited thereon unless care is 
exercised. This disadvantage may be eliminated, without also eliminating 
the advantage provided by the above described pilot projections, by 
utilizing the embodiment of FIG. 5. 
Referring to FIG. 5, it will be seen that each filter element assembly such 
as 42-42a is located within a recess such as 64 which is, in turn, located 
on the end of a projection such as 66. By the use of this configuration, 
the embodiment of FIG. 5 provides the desired restriction on the 
separational movement of the housing sections, as well as the previously 
described orienting function, and in addition allows the filter elements 
to be positioned at or near the top of the respective recess. As 
previously explained, the latter location facilitates the intact removal 
of the filter elements by minimizing particle-dislodging prying movements. 
It will be understood that, as was the case with FIGS. 1 through 4, the 
embodiment of FIG. 5 may be realized in a number of different forms which 
differ from one another in matters such as the distribution of recesses 
and projections among the housing sections. 
While the present invention has been described with reference to various 
specific embodiments, it will be understood that the true scope of the 
present invention is to be determined only with reference to the appended 
claims.