Self-cleaning air filter

An improved self-cleaning air filter (2) of the pulse jet type. The filter includes at least one filter element (20) located in a dirty air plenum (6) which is separated from a clean air plenum (8). A valve (64) directs a cleaning jet of gas that moves in a back flow direction along the filter element to remove accumulated contaminants therefrom. A diffuser is located in the clean air plenum for diffusing the cleaning jet of gas to convert the cleaning jet to a high volume, low pressure jet which substantially fills the entire cross-sectional area of the filter element. The filter element is releasably contained inside the dirty air plenum on elongated support members (36). Rotatable cams (44) are provided for laterally shifting the filter element to lock the filter element in place against a dividing wall (10).

TECHNICAL FIELD 
This invention relates generally to a self-cleaning air filter of the pulse 
jet type. As such this invention is useful in any engineering application 
which requires the filtering of particulate contaminants, e.g. dust, sand 
particles, etc. Such applications might include atmospheric filtering for 
air pollution control and traditional air filtering operations for 
internal combustion engines and the like. More particularly, the air 
filter which will be specifically disclosed in this application has been 
designed for use with the power plants of railroad locomotives. 
DESCRIPTION OF THE PRIOR ART 
Air filters are widely used for many purposes. For example, they have long 
been used for filtering the intake air used in the combustion cycle of an 
internal combustion engine. In addition, various other types of equipment 
often require some type of air filter. Moreover, air filters are often 
used in industrial applications, e.g. flour mills, for filtering the 
atmospheric air which is breathed by the plant workers. These latter 
applications have become more widespread with the advent of various laws 
regulating environmental conditions in industrial plants. 
Eventually, any filter medium which is used becomes clogged or "caked" with 
the various particulate contaminants which have been filtered. This 
clogged condition is often referred to as one in which the filter element 
is "loaded". If there were no effective way of cleaning the filter medium 
after it is loaded, the medium would have to be discarded after a single 
use. This is economically wasteful. It is preferable to periodically clean 
and then reuse the filter medium. 
Various types of self-cleaning air filters have long been known. These 
filters can remove accumulated contaminants from the filter medium which 
greatly extends the useful life of the medium. One method often used in 
the gas filtering industry to remove contaminants from a filter is to 
periodically reverse the direction of fluid flow through the medium. The 
contaminant then releases from the medium as large agglomerates which 
settle into a collecting chamber where they can be removed. 
One type of apparatus which is commonly used in a reverse flow 
self-cleaning air filter is one which may be referred to as a pulse jet 
type of air filter. In this filter, a pulse of compressed gas is released 
from a storage reservoir by a valve. The valve forms a jet of gas which is 
directed towards the filter medium. This jet of gas first usually enters a 
venturi which is located immediately above the filter element. The low 
pressure at the venturi throat effectively causes the ambient air 
surrounding the filter element to be drawn in with the pulse jet and 
directed downwardly into the filter in a "back flow" type of operation. 
Thus, the venturi effectively converts a small volume of high pressure air 
into a large volume of low pressure air which travels down the filter 
medium. 
However, the venturi type of apparatus noted above has a number of distinct 
disadvantages. It is useful primarily in what might be called low 
performance environments. Such environments are characterized by (1) a 
relatively large amount of space in which to mount the filter, and (2) a 
relatively low primary air flow velocity through a filter. For example, in 
a typical low performance application in an industrial environment (e.g. a 
flour mill), lots of room is usually available for the filter to be 
installed. Thus, size is not a critical parameter for the filter. In 
addition, the average air flow velocity through the filter medium is 
usually from 1.0-3.0 feet per minute (f.p.m.). However, a venturi is not 
usually suitable in a high performance application. Space is an important 
consideration in such applications and the average air flow velocity 
through the filter medium is on the order of 10 f.p.m. or more. A filter 
for the engine or power plant of a railroad locomotive can be classified 
as a high performance application. 
In high performance applications as identified above, a venturi type of 
pulse jet cleaning system isn't suitable for a number of reasons. First, 
the venturi is usually positioned inside the clean air plenum and is 
usually quite long and bulky. Thus, the venturi design requires a certain 
minimum amount of space for installation. This does not allow for a 
compact air cleaner design as is required in these applications. Secondly, 
at the higher average air flow velocities which are encountered in a 
typical high performance application, the pressure drop occurring across 
the conventional venturi becomes much greater. In fact, the pressure drop 
is often so large that the engine to which the filter is attached has to 
expend a considerably amount of energy in causing air to flow through the 
filter. This increases the fuel consumption of the engine which is 
obviously undesirable. 
Consequently, there is a need for some type of system for use in a pulse 
jet self-cleaning air filter which would serve to diffuse the high 
pressure jet of air across the filter element, but which does not have the 
disadvantages of a venturi. Several prior art patents have suggested 
various types of diffusers. For example, U.S. Pat. No. 3,509,698 to 
Medcalf et al. discloses a cone which is mounted below the pulse jet 
nozzle for spreading the air out into the filter element in a propagating 
wave form. However, the cone in the Medcalf arrangement is mounted inside 
a tubular extension or nozzle mounted on the top of the filter element. As 
such Medcalf does not have many advantages over a typical venturi. The 
tubular extensions add substantially to the height of the filter element. 
In addition, the cones restrict normal air flow through the filter during 
all air filtering operations since they are mounted inside the tubular 
extensions. This is true of other patents, such as U.S. Pat. No. 3,594,992 
to Carr, which disclose similar types of diffuser members. All of these 
diffusers are located in such a manner as to restrict the normal air flow 
through the filters. 
Furthermore, most of the self-cleaning pulse jet types of air filters 
include a plurality of fitler elements which are located in the dirty air 
plenum and have one end connected around an outlet opening in a dividing 
wall which forms both the dirty and clean air plenums. Some of the means 
used to support the filter elements may be quite complicated. Thus, the 
filter elements may take a great deal of time to install or replace inside 
the filter housing. There is a need for simple supporting means for the 
filter elements inside the filter housing which can be used to quickly and 
easily replace the filter elements. In addition, in any high performance 
filter application, the supporting means for the filter elements must be 
compact. 
SUMMARY OF THE INVENTION 
One aspect of this invention relates to a pulse jet self-cleaning air 
filter having means for diffusing the jet of gas to substantially fill the 
cross-sectional area of the filter element at the element outlet opening. 
The diffusing means is located in the clean air plenum so as not to 
restrict the normal air flow through the filter during air filter 
operations. 
In addition, another aspect of this invention is an air filter having means 
for quickly and easily aligning and securing one or more filter elements 
inside the filter housing. 
The air filter of this invention comprises a housing which includes a dirty 
air plenum and a clean air plenum defined by a partition having at least 
one outlet opening therein. A filter element is installed inside the dirty 
air plenum with one end of the filter element being sealed around the 
outlet opening. Means for generating a cleaning jet of gas and for 
directing that jet into the filter element is provided. A diffuser is 
mounted in the clean air plenum and is spaced above, i.e. away from, the 
separating partition. The diffuser serves to spread the jet of compressed 
gas to substantially fill the cross-sectional area of the filter element, 
but because of its location does not restrict the normal air flow through 
the filter element nor does it engender an appreciable pressure drop 
across the filter element. 
The air filter of this invention relates to an improved means for 
supporting the filter elements inside the dirty air plenum of the housing. 
This supporting means comprises a pair of spaced, elongated rails on which 
the ends of each filter element roll. Each rail has a shallow concave 
seating area which receives the filter element therein. The filter element 
can be laterally slid in each of the seating areas such that the filter 
element can be sealed around one of the outlet openings in the separating 
partition.

DETAILED DESCRIPTION 
This invention comprises an improved self-cleaning air filter of the pulse 
jet type having a number of novel features. An air filter according to 
this invention is generally indicated as 2 in the drawings. Air filter 2 
as disclosed herein is designed for use in filtering the intake air for 
the power plant of a railroad locomotive. However, air filter 2 is not 
limited for use with locomotives. In fact, filter 2 may be used with 
conventional internal combustion engines or for any other appropriate air 
filtering purposes such as atmospheric air filtering in various industrial 
applications. However, air filter 2 is primarily designed for high 
performance applications, i.e. applications requiring a compact air filter 
design and having relatively high average velocities of air flow through 
the filter element, e.g. 10 f.p.m. or more per unit area. 
Air filter 2 comprises a filter body or filter housing generally designated 
as 4. Housing 4 includes a substantially rectangular "dirty air" plenum 6 
and an adjoining rectangular "clean air" plenum 8. "Dirty air" and "clean 
air" are terms of art which refer, respectively, to a gas that is laden 
with various particulate contaminants and a gas which is not laden with 
these contaminants and a gas having been filtered. A separating partition 
or dividing wall 10 in housing 4 fluidically isolates dirty air plenum 6 
from clean air plenum 8 except insofar as a plurality of substantially 
circular outlet openings 12 are concerned. The purpose of the outlet 
openings 12 contained in wall 10 will be described hereafter. 
A substantially rectangular air intake 14 is provided in dirty air plenum 6 
to allow contaminant laden or dirty air to pass into the plenum. 
Similarly, an air outtake 16 is located in clean air plenum 8 for 
conducting clean filtered air outwardly. Air filter 2 will be suitably 
connected to the power plant of a locomotive engine (not shown). Air will 
be sucked through filter 2 during an air filtering operation with the air 
passing into air intake 14, through the dirty air plenum 6, into the clean 
air plenum 8, and outwardly through the clean air outtake 16. The 
direction of this air movement is generally indicated by the arrows A. 
The bottom of dirty air plenum 6 is open and leads to a contaminant 
collecting hopper generally indicated as 17 in FIGS. 2 and 3. An outlet 
conduit 18 is connected to the contaminant collecting hopper at the very 
bottom thereof. Any suitable contaminant removal device (not shown) may be 
located at the bottom of hopper 17 adjacent conduit 18. Hopper 17 serves 
to collect contaminants which have been cleaned from a plurality of filter 
elements contained in dirty air plenum 6. The removal device and the 
conduit 18 serve to remove the contaminants which have been separated from 
the filter element. This structure is typical of many conventional pulse 
jet self-cleaning air filters. 
A plurality of filter elements, generally designated as 20, are releasably 
mounted inside dirty air plenum 6 for filtering the air passing 
therethrough. Each filter element 20 is generally identical. Referring to 
FIG. 1, filter element 20 includes a hollow, cylindrically shaped filter 
medium 26 made from any generally conventional filter materials. For 
example, filter medium 26 preferably comprises a cylinder made of a 
longitudinally pleated paper filter medium. Referring to the arrows A, air 
which is being filtered passes from the exterior of the filter element 20 
into the interior hollow bore 27 of the cylindrical filter medium 26. 
Thus, the contaminants which have been filtered from the air will be 
retained on the exterior surface of the filter medium 26. 
The opposed ends of filter medium 26 are respectively fixedly bonded to 
cylindrical end plates 22 and 24. In effect, end plates 22 and 24 form 
rims for the filter element 20 on which filter element 20 can be rolled. 
The end plate 24 has a circular opening therein which is the same size and 
is designed to mate with the outlet opening 12 in wall 10. A circular 
gasket 28 is located on the exterior surface of end plate 24. Gasket 28 is 
slightly larger than the diameter of outlet openings 12 in an air-tight 
manner when the filter element 20 is forced against wall 10 as described 
in more detail hereafter. 
One side of the dirty air plenum 6 is closed by a removable access cover 
30. Access cover 30 is removably attached to dirty air plenum 6 by a 
plurality of bolts, screws or the like generally designated as 32. As 
shown in FIG. 4, there are six outlet openings 12 provided in the wall 10. 
These outlet openings 12 are arranged in two rows of three openings each. 
Thus, a rectangular array of six filter elements 20 is designed to be 
contained inside dirty air plenum 6. Each filter element 20 will seal 
around one of the outlet openings 12. 
An improved means for supporting the filter elements 20 inside dirty air 
plenum 6 is generally indicated as 34. Supporting means 34 includes two 
spaced and elongated support members or rails 36. Support members 36 are 
fixedly mounted respectively on opposed side walls of the dirty air plenum 
6. There are two pairs of these support members 36 with one pair being 
provided for each row of the filter elements 20. Thus, three filter 
elements 20 are supported on each pair of support members 36. 
Support members 36 include means for securely seating each filter element 
20 thereon in an aligned relationship with one of the outlet openings 12. 
This seating means includes three pairs 37, 38 and 39 of concave shaped 
recesses 40 located in the upper surfaces of support members 36. The 
recesses 40 in each pair 37-39 are located on the opposed support members 
36 and are aligned with one another. Thus, one recess 40 is provided for 
each end plate 22 and 24 of filter elements 20. The shape of the recesses 
40 corresponds to the peripheral shape of the end plates 22 and 24 to 
allow filter elements 20 to become seated in the recesses. In addition, 
recesses 40 are laterally elongated in a lateral direction indicated as 
41. This allows the filter elements 20 to be laterally movable relative to 
support members 36. 
In addition, supporting means 34 includes a selectively actuable means, 
generally indicated as 42 in FIG. 5, for laterally sliding or forcing each 
filter element in the lateral direction 41 towards dividing wall 10. This 
forcing means 42 comprises a plurality of rotatable cams 44 which are 
designed to engage against the end plates 22 of each filter element 20. 
Two cams 44 are provided for each filter element 20. Cams 44 are fixedly 
mounted on an elongated shaft 46 which passes through the dirty air plenum 
6. Shaft 46 is rotatably journalled inside the dirty air plenum 6 by means 
of suitable bearing blocks 48. Two such shafts 46 are mounted in plenum 6 
for use with each row of the filter elements 20 on the vertically spaced 
pairs of support members 36. See FIG. 3. The end of shaft 46 carries a 
conventionally shaped bolt head 50 located inside plenum 6. Shaft 46 can 
be manually rotated by applying a wrench to bolt head 50 and rotating the 
wrench. Rotation of shaft 46 will rotate the cams 44 from an inoperative 
position, shown in phantom in FIG. 5, to a operative position, shown in 
solid lines, at which cams 44 engage filter elements 20. 
To install filter elements 20 in dirty air plenum 6, access cover 30 is 
first removed. Each filter element 20 is then placed onto the support 
members 36 with each end plate 22 and 24 being respectively received on 
the top surface of one of the support members 36. Filter elements 20 are 
then simply rolled along support members 36 by virtue of the rolling 
engagement between the circular end plates 22 and 24 and the top surface 
of the support members 36. Whenever the filter element 20 comes to one 
pair 37, 38 or 39 of the recesses 40, filter element 20 becomes seated in 
the recesses 40 and stops rolling. However, the filter element 20 can be 
manually pushed out of the recesses 40 to continue rolling down the 
support members 36 until all three pairs 37-39 of the recesses 40 are 
filled with filter elements 20. Thus, six filter elements 20 are installed 
on the two pairs of support members 36 by simply rolling the filter 
elements 20 down the support members until they become properly seated in 
the appropriate pair of the recesses 40. During this placement of filter 
elements 20, cams 44 are rotated into their inoperative position. In this 
position the cams 44 clear the end plates 22 allowing the filter elements 
20 to be installed on support members 36. 
After all six filter elements 20 are installed on the support members 36 
and are received in one pair of the recesses 40, the shaft 46 is manually 
rotated by applying a wrench to bolt head 49. This causes cams 44 to be 
moved from their inoperative position to their operative solid line 
position in FIG. 5. In the operative position of the cams 44, they engage 
the end plates 22 and slide the entire filter element 20 in the lateral 
direction 41. Because the recesses 40 are laterally elongated, the 
necessary lateral movement of filter element 20 is allowed. This lateral 
movement will force end plate 24 toward dividing wall 10. This compresses 
gasket 28 around one of the openings 12 and effects an air-tight seal of 
the end of filter element 20 relative to wall 10. Cams 44 securely lock 
the filter elements 20 in place against wall 10. Thus, when both of the 
shafts 46 have been rotated as noted above, all of the filter elements 20 
will be sealed against one of the outlet openings 12. Access cover 30 may 
then be reinstalled on the dirty air plenum 6. Air filter 2 is then ready 
for an air filtering operation. 
An interlock means 50 is provided on access cover 30 for preventing the 
cover 30 from being installed if filter elements 20 have not been locked 
into position against the dividing wall 10. Interlock means 50 simply 
comprises two horizontally extending finger or latches respectively 
identified as 52 in FIGS. 1 and 3. Latches 52 extend inwardly from access 
cover 30 at a location which generally corresponds to the location of cams 
44. One latch 52 is provided for each set of cams 44, i.e. one latch 52 is 
generally located immediately above each shaft 46. 
Latches 52 will clear the cam 44 located closest to cover 30 only when the 
cams are in their operative solid line position. See FIG. 3. If the cams 
44 are sticking up in their inoperative position, meaning that the filter 
elements 20 have not yet been locked against wall 10, then the latches 52 
will abut the cams 44 located adjacent cover 30. This prevents cover 30 
from being installed on the dirty air plenum 6. Only when all the cams 44 
have been rotated downwardly will the latches 52 clear the cams and allow 
cover 30 to be installed. Thus, interlock means 50 is an important safety 
feature. It prevents the operator from installing the access cover 30 and 
conducting an air filtering operation when he has inadvertently failed to 
lock all the filter elements 20 in place. 
Supporting means 34 as described herein is particularly simple and 
efficient. In order to install the filter elements 20, it is only 
necessary to roll the filter elements 20 down the support memebers 36 
until they are seated in their respective recesses 40. Then, simply by 
rotating the shafts 46 and hence cams 44, filter elements are transversely 
slid until they firmly engage against dividing wall 10. In addition, the 
latches 52 insure that an air filtering operation will not take place 
unless all of the filter elements 20 are properly locked in place by 
rotation of cams 44. Thus, the supporting means 34 described herein can be 
used to quickly and easily install filter elements 20 in dirty air plenum 
6. Since filter elements 20 will have to be replaced from time to time, 
the ease with which the supporting means 34 allows such replacement is 
obviously desirable. 
Another aspect of this invention relates to a pulse jet cleaning means for 
the air filters 20 which is generally indicated as 60 in FIGS. 1-3. 
Cleaning means 60 includes a source of compressed gas under a suitably 
high pressure. This source of gas is preferably a compressed air manifold 
62 located on the exterior of clean air plenum 8. A plurality of valves 64 
have their inlets connected by conduits 66 to the compressed air manifold 
62. The outlets of valves 64 are connected by elongated conduits 68 to 
nozzles 70. See FIG. 3. One valve 64 and one nozzle 70 is provided for 
each of the filter elements 20. 
Each nozzle 70 is located inside clean air plenum 8 on any suitable support 
rod 72 or the like. As shown in FIG. 3, each nozzle 70 points along a 
longitudinal axis 74 through the center of each cylindrical filter element 
20. Nozzles 70 are suitable for directing cleaning jets of compressed gas 
along the axes 74. These cleaning jets are normally high pressure air 
since the compressed gas in manifold 62 comprises a high pressure air. 
Control means (not shown) are provided for periodically operating the 
valves 64 to periodically pulse jets of compressed air through the filter 
elements in a reverse back flow direction. This direction is indicated by 
the arrow B in FIGS. 1 and 2. This is a typical structure and method of 
operation for a pulse jet self-cleaning air filter. 
This invention relates generally to the use of a diffuser means indicated 
as 80. Diffuser means 80 comprises a V-shaped deflector plate 82 located 
between each nozzle 70 and the corresponding outlet opening 12. Deflector 
plate 82 has an apex 84 and two outwardly angled sides 86. Deflector 
plates 82 are located inside the clean air plenum 8 a substantial distance 
from the outlet openings 12 and wall 10. 
Preferably, deflector plates 82 comprise sheet metal fabrications which 
extend from the top of clean air plenum 8 to the bottom. A single 
elongated angle forms the deflector plates 82 for two nozzles 70 since the 
nozzles 70 are generally in line corresponding to the in line orientation 
of the various filter elements 20 in the two vertically spaced rows. See 
FIG. 3. Deflector plates 82 diffuse or spread out the cleaning jet of gas 
to substantially fill the cross-sectional area of the outlet opening 12 
and hence filter elements 20. In other words, deflector plates 84 convert 
the relatively low volums, high pressure cleaning jet issuing from the 
nozzles 70 to a low pressure, high volume cleaning jet. In addition, 
deflector plates 82 direct the cleaning jet substantially down the entire 
cross-sectional area of the filter elements 20 to form a more effective 
cleaning jet, i.e. the jet is directed directly against filter medium 26. 
In addition, a quantity of the low pressure surrounding gas in plenum 8 
will still be entrained with the cleaning jet as is typical in the case of 
a venturi type of pulse jet cleaning system. 
The particular diffuser means 80 noted herein is advantageous because it 
replaces the venturi which is conventionally used in a pulse jet type of 
self-cleaning air filter. This greatly decreases the size needed for clean 
air plenum 8 and allows a compact air filter design. Such compactness is 
important in high performance air filter applications. In addition, there 
is no longer any appreciable pressure drop encountered by the normal air 
flow during an air filtering operation since a venturi is no longer used. 
Furthermore, deflector plates 82 are located sufficiently far away from 
the wall 10 such that they do not provide any substantial obstruction to 
the normal air flow through filter 2 during an air filtering operation. 
Thus, the deflector plate 82 provides all of the advantages of a 
conventional venturi, i.e. it diffuses or spreads out the cleaning jet to 
substantially fill the filter element 20, but it does not have any of the 
disadvantages of the venturi or the other deflectors commonly known in the 
prior art. 
Thus, the important design criterions for the deflector plates 82 include 
the fact that it is located in the clean air plenum 8 sufficiently far 
above the outlet openings 12 to not pose any appreciable obstruction to 
the flow of air therethrough. In addition, the design of the deflector 
plate and its distance from the nozzles 70 has to be selected to insure 
that the cleaning jets substantially fill the cross-sectional area of the 
outlet openings 12 at the location of the separating wall 10. Tests have 
indicated that pulse quality degrades as the distance between the nozzle 
70 and the deflector plates 82 decreases and as the diameter of the outlet 
opening 12 increases. These results indicate that the quality of the 
cleaning jet is therefor dependent on the percentage of the outlet opening 
12 which is "filled" by the cleaning jet. Unless substantially all of the 
outlet opening 12 is filled by the cleaning jet, at least some of the air 
which is otherwise present inside filter element 20 will not be carried 
along in the backflow through the medium. This air will thus leak out of 
the outlet opening 12 in the direction A even when the cleaning jet is in 
operation. This is a disadvantageous result. 
Another important advantage of the present invention should be emphasized. 
It has been found that the present invention cleans the filter element 20 
better than a venturi type system even though the pressure pulses used in 
the cleaning jet were comparable. Apparently, because of the shape of the 
venturi, i.e. the curved walls of the venturi, the cleaning jet which is 
formed by the venturi is less effective near the open end of the filter 
element and more effective at the closed end thereof. By open end of the 
filter element it is meant that end which is adjacent outlet opening 12. 
Unfortunately, the filter elements 20 tend to load or cake with dust more 
heavily near the open end rather than the closed end. The cleaning jet 
formed by the deflector plate 82 tends to clean the open end of the filter 
element much more effectively than the venturi since the cleaning jet is 
better directed and more fully expanded at the open end of the element 
when the deflector plates 82 are used. This will result in superior life 
for the filter element 20 even when the internal element pressures are 
comparable. Superior cleaning of the filter elements by the present 
invention near the open end of the filter element has been verified by 
observing deposits on the filter element at the conclusion of life tests. 
Another feature of the present invention is that the filter elements 20 are 
horizontally arranged inside the dirty air plenum 6 and that the air 
intake 14 is located in the top wall of plenum 6. In addition, the hopper 
17 which collects the contaminants released from the filter element is 
located generally beneath the elements. Thus, the normal air inflow 
through air intake 14 will be in a generally vertical downward direction 
before the flow enters into the elements 20 and is carried through the 
outlet openings 12. Consequently, whenever the cleaning jets have been 
used to release dust or other contaminants from the filter elements 20, 
the normal air flow through the air filter 2 tends to carry those 
contaminants downward into the hopper 17. Thus, the arrangement of the 
components mentioned above serves to ensure that all the contaminants 
released from the filter element 20 will be collected in the hopper 17 
where they may be later removed. 
Referring now to FIGS. 3-6, another feature of the invention will be 
described. It has been found that dust will eventually cause the filter 
elements 20 to become so contaminated that they must be replaced. During 
such replacement, the cams 44 are rotated to an inoperative position, the 
filter elements 20 are moved laterally to their dotted line positions in 
FIG. 5, and are then rolled outwardly from plenum 6. During this removal 
process, it has been found that dust which is caked near the open end of 
the filter element 20, i.e. around the end plate 24 and gasket 28, will 
tend to be released from that end of the filter element and fall through 
the outlet opening 12 into the clean air plenum 8. This dust will then be 
carried into the engine with which the air filter 2 is used when the air 
filter is next put into operation. This is an obviously undesirable result 
as it defeats the very purpose of air filter 2. 
To prevent the above-identified problem from occurring, the present 
invention utilizes a plurality of semi-circular baffles, each of which is 
generally indicated as 90, around each of the outlet openings 12. 
Referring to FIG. 4, only one such baffle 90 is shown in solid lines 
around one opening 12 although it should be understood that six such 
baffles for each of the six openings 12 are provided. See FIG. 3. Baffles 
90 are slightly larger in diameter than the diameter of the filter element 
20 and closely surround the top half of the open end of filter element 20. 
These baffles prevent dust from accumulating in large quantities around 
the open end and prevent that dust from entering into the clean air plenum 
8 when the filter elements 20 are replaced. Thus, baffles 90 serve as an 
effective means for preventing any dust contamination of clean air plenum 
8 during filter element replacement. 
However, use of the baffles 90, which is desirable, but which is not 
strictly necessary to the basic principles of this invention, complicate 
somewhat the task of removing the filter elements 20. This complication 
arises because the end plates 22 and 24 on each of the filter elements 
tend to "catch" or hang up on either the cams 44 or the baffles 90 
respectively. To prevent this, a plurality of outwardly extending tabs 92 
are located between each of the baffles 90 on the separating wall 10. Tabs 
92 extend outwardly from wall 10 a greater distance than the baffles 90 
and thus effectively prevent the end plates 24 from catching on the 
baffles 90. In addition, an elongated guide member or rail 96 is mounted 
on that face of the cams 44 which is vertical when the cams are in their 
inoperative position as shown in dotted lines in FIG. 3. Rail 96 spans and 
is attached to all of the cams 44 on any given shaft. The rail 96 serves 
to engage the end plate 22 and guide that end plate in a direction away 
from the cams 44 to straighten the filter element 20 whenever the filter 
element has a tendency to become cocked relative to support members 26. 
Obviously, the distance between the end of the tabs 92 and rail 96 during 
removal of the filter element 20 must be slightly greater than the length 
of the filter element. 
In addition, use of the outwardly protruding tabs 92 is also advantageous 
for another reason. For example, if one of the filter elements 20 is not 
properly seated in one of the opposed pairs 37-39 of recesses 40, it might 
be possible nonetheless to rotate the cams 44 to their operative position 
by laterally pushing the filter elements 20 towards the dividing wall 10. 
Thus, operation of the filter 2 could conceivably take place even when one 
or more of the filter elements 20 was not properly seated and sealed 
around the outlet opening 12. However, by using the outwardly protruding 
tabs 92, any substantial lateral movement of the filter element 20 is 
stopped by virtue of the engagement of the end plate 24 with one of the 
tabs 92. Thus, unless each of the filter elements 20 is properly seated in 
the recesses 40, it becomes impossible to actuate the cams 44 to their 
solid line operative position. Such an indication would mean that one of 
the elements 20 was misaligned inside plenum 6 and would be a valuable 
safety feature for operating the filter 2. 
Various modifications of this invention will be apparent to those skilled 
in the art. For example, the diffuser means 80 may comprise a cone or 
other type of form which will cause effective diffusion of the jet, i.e. a 
pyramidal shape. Furthermore, it is not necessary that the filter element 
20 include a pleated filter medium 26. The diffuser means 80 taught herein 
may be used with other types of filter elements including elongated bag 
type filters. Furthermore, the support members 36 are preferably 
perforated rather than being solid over the length thereof. This prevents 
dust from becoming built up on the support members 36 which would 
otherwise hamper removal of used filter elements 20 from the air filter 2. 
Thus, the scope of this invention is to be limited only by the appended 
claims.