Self-cleaning air filter system

A self-cleaning impingement type air filter unit is mounted on a flexible elastomeric support member comprising an end wall of a filter housing exposed to the pressure differential between the interior housing chamber and the ambient pressure of the clean air discharge conduit. A standard pleated paper type porous media filter element is mounted on the flexible wall member and includes a support plate on which a mechanical vibrator is mounted whereby the complete filter element is mechanically oscillated to dislodge accumulated material on the surface of the filter media. The filter support structure includes a mounting flange which is adapted to be supported on a filter housing by yieldable springs which permit movement of the entire filter element and support structure to function as a pressure relief valve to limit the pressure differential across the filter housing. The system is particularly adapted for use with bulk material conveying systems operating at relatively low conveying air pressures of approximately 15 psig.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention pertains to a porous media impingement type air 
filter system including a filter unit which is operably connected to a 
mechanical vibrator and is supported on a flexible wall member forming a 
closure of one end of the filter chamber. The filter unit is adapted for 
use in conjunction with pneumatic bulk material conveying systems. 
2. Background Art 
In the art of porous media impingement or barrier type filter systems used 
for filtering dust and particulate matter out of a moving air stream, it 
has always been a problem to prevent unwanted clogging of the filter by 
accumulation of caked material on the filter media. The filter media must, 
inherently, accumulate particulate material in the performance of its 
function. However, continued accumulation of material eventually reduces 
the fluid flow area through the filter and increases the flowstream back 
pressure. 
Several techniques have been developed to provide for the so called 
self-cleaning of impingement or barrier type air filter units. One 
approach involves providing apparatus for producing periodic pulsed jets 
or blasts of high velocity air in the reverse direction of the normal flow 
of air through the filter element to knock accumulated material off of the 
media. Such systems typically require a relatively high pressure source of 
compressed air to provide sufficient energy of the reverse flow to remove 
material accumulated on the filter media. This is particularly true for 
the preferred type of filter units which have a substantially rigid 
cylindrical element including a pleated media such as porous paper or 
similar material. 
Another technique which has been developed for impingement or barrier type 
air filter units pertains to various arrangements for vibrating the filter 
element to periodically or continuously effect the removal of accumulated 
particulate material on the filter media. Known types of mechanical 
vibrating systems require specialized filter element structures such as, 
for example, the type of system wherein the filter element structure 
itself including the filter media is mechanically twisted or deflected to 
remove the accumulated material. This type of filter media cleaning system 
has the disadvantage of shortening the life of the filter due to 
mechanical fatigue of the filter media and adjacent supporting structure 
which is constantly being flexed or deflected. 
Several other mechanical vibrating systems have been developed for various 
types of porous media impingement filters, all of which are relatively 
mechanically complex and are relatively unreliable due to the fact that 
the structure around and including the filter element is being constantly 
stressed in a cyclic manner resulting in early fatigue failure of one or 
more parts of the structure. 
Accordingly, there has been a longfelt need for a self-cleaning type filter 
system which is adapted to utilize the preferred type of filter element 
characterized by a pleated porous media supported by associated structure 
which forms a substantially rigid and easily fabricated unit. Such types 
of filter elements have not easily lent themselves to use in connection 
with mechanical vibrating devices for continuously or periodically 
cleaning the filter media by vibrating or shaking the entire filter unit. 
However, the present invention provides an arrangement which mechanically 
vibrates the filter element with a particularly advantageous structure 
which is adapted for several filtering applications. In particular, one 
embodiment of the self-cleaning air filter system of the present invention 
is adapted for used in conjunction with pneumatic bulk material conveying 
systems and the like. 
SUMMARY OF THE INVENTION 
The present invention provides a unique self-cleaning air filter system of 
a type wherein mechanical vibration or oscillation of a filter unit is 
provided as a means of continuously or periodically removing accumulated 
dust or particulate material from the surface of a filter element having 
impingement or barrier type filter media. 
In accordance with one aspect of the present invention, there is provided a 
self-cleaning air filter apparatus comprising a replaceable filter unit 
having a pleated porous media filter element wherein the filter unit is 
connected to a mechanical vibrator device and is supported by structure 
including a flexible wall member which delimits a portion of a filter 
chamber in which the filter unit is disposed. By mounting the filter unit 
on a resilient flexible wall member, the entire filter unit may be 
vibrated or oscillated to remove particulate material accumulated on the 
filter element. In this way, reduced stress and strain is imposed on the 
filter element itself. This arrangement is particularly advantageous for 
filters wherein the filter element comprises a porous media of 
substantially rigid material and which is normally supported by a light 
metal or plastic structure. The flexible wall member also forms a portion 
of the filter housing exposed to the pressure differential of the fluid 
pressure within the housing versus the ambient atmospheric pressure 
outside of the housing. 
The present invention also provides for using standard commercial porous 
media filter elements which may be adapted to be used in conjunction with 
a vibratory type cleaning system without modifying the filter element 
itself. Moreover, the filter element mounting arrangement provides for 
vibratory cleaning of the filter media without substantially twisting or 
deflecting the media material thereby prolonging the life of filter units 
and associated structure since the entire filter unit is vibrated and is 
substantially isolated from its supporting structure by the resilient 
flexible wall member. 
The present invention also provides an improved air filter system including 
a filter unit which also functions as a pressure relief valve when mounted 
on a filter housing normally exposed to fluid pressure greater than the 
surrounding ambient atmospheric pressure. Accordingly, the filter system 
of the present invention is particularly useful for applications wherein a 
limit pressure must be maintained within the system which is supplying 
pressure air to the filter housing. In accordance with the present 
invention, the supporting structure for the filter unit includes a flange 
member which may be mounted on a cooperating flange formed on a filter 
housing and wherein the entire filter unit including the supporting flange 
member may be yieldably biased into a sealing position against the housing 
flange but is movable to provide a pressure relief flow passageway for 
pressure air when a limit pressure differential across the filter element 
is experienced or when a maximum limit pressure within the filter element 
housing and associated pressure conduit system is experienced. 
Accordingly, with such an arrangement, the filter element is normally 
prevented from collapsing and the chance of structural failure of the 
pressure vessel system is minimized. 
The present invention still further provides an improved self-cleaning air 
filter system which is particularly adapted for filtering a pressure air 
flowstream having relatively large concentrations of entrained particulate 
matter such as are experienced in pneumatic bulk material conveying 
systems. The overall arrangement of the self-cleaning filter unit, it 
supporting structure and the provision of fluid pressure relief means is 
particularly advantageous for use in combination with material conveying 
systems such as pneumatic unloading systems for bulk material transport 
vehicles and similar apparatus. 
Additional advantages and superior features of the self-cleaning air filter 
system of the present invention will be appreciated by those skilled in 
the art upon reading the detailed description which follows in conjunction 
with the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In the description which follows, like parts are marked throughout the 
specification and drawings with the same reference numerals, respectively. 
The drawings are not necessarily to scale and the scale may be exaggerated 
in certain views to better illustrate the salient features of the 
invention. 
Referring to FIGS. 1, 2 and 3, the self-cleaning filter system of the 
present invention is illustrated in a form which is adapted as an air 
filter apparatus, generally designated by the numeral 10. The filter 
apparatus 10 includes a generally cylindrical housing 12 having opposed 
end flanges 14 and 16 formed as an integral or fixed part of the housing, 
respectively. The filter apparatus 10 is adapted to be mounted on a 
housing 18 having an interior chamber 20 into which a flowstream of air 
laden with particulate matter may be introduced through a conduit 22. The 
conduit 22 and the interior chamber 20 may be configured to provide for 
inertial and gravitational separation of some of the particulate material 
entering the chamber wherein the separated material may drop into a bin or 
hopper portion of the housing 18, not shown. The air flow then enters a 
chamber 24 formed by the housing 12 and further, separation of entrained 
particulate material is performed by the filter system of the present 
invention. 
The filter apparatus 10 is further characterized by a filter unit, 
generally designated by the numeral 26, which is of the porous media 
impingement type and includes an element 27 which comprises a generally 
cylindrical member having a filter media 28 made of relatively stiff 
paperlike material having a porosity which is pervious to air but which 
has the capability of entrapping fine particles entrained in the air 
flowstream. The filter media 28 is preferably arranged in a series of 
pleats 29, FIG. 2, and is supported between respective inner and outer 
cylindrical perforated metal support walls 30 and 31. The element 27 also 
includes upper and lower end caps 32 and 33 which are suitably secured to 
the walls 30 and 31 to form a substantially rigid structure. Accordingly, 
air passing through the pleats of the media 28 from the wall 31 and 
inwardly through the wall 30, enters a chamber 34 and flows upwardly 
through the chamber and to the exterior of the housing 12 through an 
annular passage 36. The filter element 27 is of a type which is 
commercially available and is representative of the state-of-the-art in 
high capacity impingement type air filter devices. The filter element 27 
in itself is not a part of the instant invention and a further detailed 
description of the element is not believed to be necessary to practice the 
invention 
Referring particularly to FIGS. 1 and 3, the filter element 27 is arranged 
to be supported by improved structure in accordance with the present 
invention and including a support plate generally designated by the 
numeral 40. The support plate 40 is a substantially rigid member 
preferably made of steel or a similar engineering material. The plate 40 
includes an annular filter element locating collar 42 and a plurality of 
vertically extending gusset members 43 which support an elongated mounting 
bolt 44. The bolt 44 extends centrally through the interior of the element 
27 and includes a threaded portion on its distal end for securing the 
element to the support plate by a nut 45 engaged with the bottom plate 33. 
A resilient seal ring 46 is preferably interposed between the element 27 
and the underside of the plate 40, as shown in FIG. 1. The support plate 
40 also includes a vertically upstanding flange part 48 which is adapted 
to have mounted thereon a mechanical vibrator device generally designated 
by the numeral 50. The vibrator 50 is of a type which may be electrically 
or pressure fluid operated and a preferred type is a vibrator manufactured 
by Vibco, Inc. of Wyoming, R.I. as their model BV380. Referring 
particularly to FIG. 3, it may be seen that the support plate 40 includes 
a plurality of circular sector shaped openings 52 formed between the 
gusset members 43 to provide a flow passage for air to flow from the 
interior chamber 34 to the annular passage 36. 
In accordance with a particuarly advantageous feature of the present 
invention, the filter element 27 and its support plate 40 are adapted to 
be secured to a cylindrical flexible wall member 54 which also forms an 
end wall of the housing 10 and delimits the chamber 24. The resilient 
support member 54 is preferably made of a flexible material such as a 
reinforced elastomer. The support member 54 is secured to the filter 
support plate 40 by a rigid metal support ring 56 and a series of threaded 
bolts or studs 58 secured to the plate 40 and arranged in a suitable 
circular pattern on the plate. The support member 54 is also secured to an 
annular mounting flange 60 by a substantially rigid annular backing plate 
62 and a series of bolts 64 arranged in a circular pattern, as shown in 
FIG. 3. The backing plate 62 preferably extends radially inwardly to a 
point adjacent the outer circumference of the support ring 56 to thereby 
serve as a backing or support member over a major portion of the annular 
area of the support member 54 defined between the inner circumferential 
edge 61 of the flange 60 and the outer circumferential edge of the support 
ring 56. The bolts 64, which secure the backing member 62 to the flange 60 
also function to secure a cylindrical gasket member 70 to the underside of 
the flange 60 to form a seal between the flange 60 and the mounting flange 
14 of the housing 12. A rigid annular support collar 72 is interposed 
between the heads of the bolts 64 and the gasket 70. 
The assembly of the filter unit 26, including the mounting flange 60, is 
further provided with a cylindrical air flow directing collar 74 suitably 
fixed to the backing member 62. A circular pattern of threaded members 76 
project vertically, viewing FIG. 1, from the backing member 62 and are 
adapted to support a cylindrical air flow deflector and shield member 78 
spaced from the collar 74 to form the flow passage 36. The shield 78 is 
characterized as an inverted shallow pan shaped member which provides a 
bonnet or rain cap to cover the air flow passages 52 and the vibrator 50. 
As shown in FIG. 3, the vibrator 50 is arranged to be supplied with 
pressure fluid through flexible inlet and exhaust conduits 80 and 82 which 
are suitably coupled to bulkhead type connector members 81 and 83 
extending through the sidewall of the collar 74. The sidewall of the 
shield 78 is suitably recessed adjacent the connectors 81 and 83 to permit 
the vibrator 50 to be connected to a source of pressure fluid such as 
relatively low or high pressure compressed air or hydraulic fluid. The 
aforementioned preferred type of vibrator provides for orbital or 
oscillatory vibration in a direction generally perpendicular to the 
longitudinal axis of the rod 44, although the filter may be vibrated in a 
direction parallel to the rod axis. 
The arrangement of the filter unit 26 and the associated supporting 
structure is also advantageously adapted to function as a pressure relief 
valve for limiting the differential pressure between the air pressure in 
the chambers 20 and 24 and exterior atmosphere. The flange 60 is adapted 
to be secured to the flange 14 by a plurality of spaced apart elongated 
bolts 90 which extend from the flange 14 through respective clearance 
holes 91 in the flange 60 and also through tubular collars 92. The collars 
92 also extend through clearance holes in the gasket 70 and engage the 
upper surface of the flange 14. The bolts 90 are each secured by a 
conventional nut 94 and a washer 96 which is engaged with a coil spring 98 
compressively secured between the washer and the upper surface of the 
flange 60. The nuts 94 are tightened until the washers 96 engage the 
collars 92, as shown in FIG. 1. 
Under the urging of sufficient pressure force acting across the axially 
projected cross-sectional area within the inner surface of the housing 
wall 13, the filter unit and the flange 60 will lift away from the flange 
14 to provide for air to flow out of the chamber 24 directly to 
atmosphere. By selecting the tubular collars 92 to be of a predetermined 
length for a given force-deflection characteristic of the springs 98, the 
pressure required to lift the flange 60 may be predetermined. 
Accordingly, the filter unit 26 also provides a pressure relief valve which 
may be set to relieve the pressure within the chamber in which the filter 
element is disposed in the event that the pressure differential between 
the chamber 24 and the atmosphere approaches a limit which might collapse 
the element 27 or rupture the filter media 28. Moreover, the pressure 
relief valve function provided by the structure shown and described may 
also function to minimize the chance of an overpressure condition within 
the housing 18, the conduit 22 and associated structure through which the 
pressure air entering the chamber 20 is flowing. 
In the operation of the filter apparatus 10, air laden with particulate 
matter is conducted through the conduit 22 into the chamber 20 and flows 
into the chamber 24 through the filter element 27 and out through the 
chamber 34 and the passage 36 to atmosphere. In certain applications of 
the filter apparatus 10, heavy loadings of particulate material will 
eventually tend to clog the filter media 28. By operating the vibrator 50 
periodically, or continually as operating conditions may dictate, the 
entire filter element 27 is vibrated with respect to the housing 12 and 
the mounting flange 60 to dislodge material accumulated on the outer 
surface of the media 28 whereupon such material will fall down through the 
chambers 24 and 20 to a collection hopper or bin described previously. 
Thanks to the arrangement of mounting of the filter element 27 on the 
resilient wall member 54, the mechanical vibrations sustained by the 
filter element are not transmitted to the flange 60 and housing 12, but 
the entire filter element, including the supporting structure for the 
media formed by the members 30, 31, 32 and 33, is allowed to mechanically 
oscillate relatively freely to dislodge material accumulated on the filter 
media. By providing support structure which allows mechanical oscillation 
of the entire filter element 27, a minimal level of stress is imposed on 
the filter element itself and, particularly on the filter media 28. 
Moreover, the resilient support member 54 also forms an end wall of the 
chamber 24 and, thanks to the backing member 62, is capable of 
withstanding a relatively high pressure differential between the chamber 
24 and the ambient atmosphere. The support member 54 is shown against the 
surface of the backing member 62 in the drawing figures; however, under 
normal operating conditions, the weight of the filter element 27 and the 
support plate 40 will bias the member 54 downward away from the backing 
member somewhat. 
Although the arrangement of the present invention is adapted to 
substantially extend the operating life of a filter element of the type 
described, if it is necessary to change the element, this may be easily 
done by removing the bolts 90 and lifting the filter unit 26 and the 
support flange 60 out of the housing. The filter element 27 may then be 
easily removed from its supporting structure by removing the nut 45 from 
the distal end of the rod 44 and replacing the element with a similar 
member. 
Referring to FIGS. 4 and 5, an alternate embodiment of the present 
invention is illustrated in a particuarly preferred application of the 
self-cleaning filter system. FIG. 4 is a side elevation of a bulk material 
transport vehicle, generally designated by the numeral 100, which is 
adapted to include a bulk material discharge apparatus including the 
self-cleaning air filter system of the present invention. The vehicle 100 
is a typical over-the-road semi-trailer and tractor unit including an 
engine driven tractor 102 and a semi-trailer 104 having a large bulk 
material transport tank 106 mounted thereon. The tank 106 is adapted to 
contain bulk material in a particulate or somewhat powdered form such as 
various types of dry cement materials, flour, sugar or any one of a 
variety of powdered or flowable materials which may be entrained in a 
relatively low pressure air stream. The trailer 104 also includes an 
onboard source of relatively low pressure air comprising an engine driven 
blower unit 108. The air blower unit 108 includes a discharge conduit 110 
which is suitably connected to the tank 106 at longitudinally spaced 
hopper portions 107 and 109 for injecting relatively large volumes of air 
at a pressure of approximately 15 psig into the interior of the tank to 
fluidize the bulk material contained therein. The fluidized material is 
discharged from the hopper portions 107 and 109 through a conduit 112 
which extends rearwardly of the trailer to a receiver and filter unit, 
generally designated by the numeral 114. The receiver and filter unit 114 
is suitably mounted on the trailer and is provided with a bulk material 
discharge valve 116 depending from the bottom side of the receiver and 
filter unit. The valve 116 is adapted to be connected to a conduit or 
disposed over a material receiving hopper at an unloading site, not shown. 
The bulk material receiver and filter unit 114 is illustrated in some 
detail in FIG. 5. The unit 114 includes a generally cylindrical housing 
118 having a depending hopper portion 120. The bulk material conveying 
conduit 112 is connected to the housing 118 generally along a line tangent 
to the circumference of the housing so that the flowstream of air laden 
with material entering the interior chamber 122 flows in a somewhat 
cyclonic or vortical path to effect separation of a substantial portion of 
the particulate material from the air flowstream. The receiver and filter 
unit 114 also includes the air filter unit 26 mounted on a housing 124 
similar to the housing 12 and which is modified to have only an upper 
mounting flange 126. The mounting flange 126 is suitably secured to a 
flange 127 integral with the upper surface of the housing 118 whereby the 
housing 124 extends substantially entirely within the chamber 122 to 
provide a compact low profile separator unit. 
In the arrangement of the filter unit 26 in FIGS. 4 and 5, the vibrator 50 
is adapted to receive pressure air from the blower unit 108 by way of a 
branch conduit 113 connected to the air supply conduit 110. The mounting 
flange 126 is rigidly secured to the flange 127 of the housing 118 and the 
bolts 90, shown in FIG. 1, have been replaced by a plurality of studs 129 
which are threaded into the flange 126 so that the mounting flange 60 and 
the filter unit 26 may be displaced with respect to the flange 126 to 
allow the filter unit to function as a pressure relief valve for the 
receiver housing 118 and the bulk material conveying system. The collars 
92 extend through the clearance holes in flange 60 and the gasket 70 and 
rest against the surface of flange 126 as shown in FIG. 5. 
Those skilled in the art will appreciate that the filter unit of the 
present invention is particularly advantageous for use in connection with 
bulk material conveying systems such as that described herein. The source 
of pressure air need not be onboard the transport vehicle 100 but may be 
available at the unloading site from a stationary blower or other source 
of relatively low pressure air. The particularly heavy dust loadings 
experienced by the filter element 27 are conveniently handled by periodic 
timed operation of the vibrator 50 or virtually continuous operation of 
the vibrator during the unloading cycle so that the filter element may 
function to filter substantially all particulate material out of the air 
stream flowing from the chamber 122 to chamber 131 and through the filter 
element. As described above, the periodic or continuous vibration of the 
entire filter element 27 assures that accumulated dust or the like is 
removed from the surface of the filter media without unduly stressing the 
media and the associated supporting structure. Thanks to the arrangement 
of mounting of the filter element on the flexible end wall or membrane 
member 54, the total energy requirements for vibrating the filter are 
reduced and a vibrator such as the preferred type described herein may 
easily operate with air at a pressure of approximately 15 psig, thereby 
being capable of utilizing the same source of air as the bulk material 
conveying air. Moreover, the flexible wall member 54 is adapted to be 
supported in such a way that it may flex and absorb the vibrations to 
prevent transmission thereof to the rest of the filter supporting 
structure. The wall member 54 is also advantageously provided with the 
rigid backing member 62 so that the flexible wall member may be exposed to 
a pressure differential across the filter unit without being severely 
stressed or distended by pressure forces. 
A second alternate embodiment of a self-cleaning filter unit in accordance 
with the present invention is illustrated in FIG. 6. Referring to FIG. 6, 
a self-cleaning vibratory type filter unit, generally designated by the 
numeral 150, includes the filter element 27 disposed within the housing 
125 mounted on the housing 118. The filter unit 150 includes a support 
plate 152 similar to the support plate 40 but having an elongated support 
rod 154 extending upwardly from the support plate and connected at its 
upper end to a mounting bracket 155 on which a vibrator 151 is suitably 
mounted to cause reciprocal linear vibrations in the direction of the 
longitudinal axis of the rod 154. The vibrator 151 may be of the pressure 
fluid actuated reciprocating piston type or a type similar to the vibrator 
50, and oriented on the bracket to cause vibrations in the direction 
described. The opposite end of the rod 154 extends through the filter 
element 27 and is adapted to secure the element to a cylindrical rim 
portion 153 of the support plate 152. The support plate 152 is also 
provided with circular sector shaped openings to provide a flow passage 
for air to flow from the interior of the filter element upward and out of 
the filter unit. 
In the arrangement illustrated in FIG. 6, the flexible wall member for 
supporting the filter unit 150 with respect to the circular flange 126 is 
characterized as a bellows type member, generally designated by the 
numeral 156, having a plurality of accordian like folds and a lower 
inwardly turned flange portion 157 adapted to be clamped between the 
support ring 56 and the rim of the support plate 152. The opposite end of 
the bellows member 156 includes an outwardly turned flange 158 which is 
clamped to a support flange 160 having a central bore 161 formed therein. 
The flange 158 is suitably clamped between the flange 160 and a support 
ring 163 by a plurality of threaded fasteners 164, as illustrated. In a 
similar manner, the support ring 56 is secured to the rim 153 by threaded 
fasteners 165. The flexible bellows type wall member 156 may be formed of 
an elastomeric material or may also be a formed metal bellows with folds 
formed therein to permit axial movement of the filter element 27 with 
respect to the flange 160. However, the filter element 27, the support 
plate 152 and the vibrator 151, are not required to be supported by the 
wall member 156. 
The filter unit 150 includes a support bracket 166 including somewhat 
vertically extending spaced apart webs 167 which extend between an upper 
hub portion 168 and a lower annular rim 169. The rim 169 is adapted to be 
secured to the flange 160 by the fasteners 164 in assembly with the 
support ring 163 and the bellows flange 158. The upper surface of the hub 
168 is adapted to support a shield or cap 170 having a downwardly turned 
rim portion 171 to serve as a weather shield and to provide for 
redirecting the flow of dust free air leaving the filter unit 150. A coil 
spring 172 is interposed between a backing plate 174 on top of the shield 
170 and the support bracket 155 for the vibrator 151. 
As illustrated also in FIG. 6, the support rod 154 is threaded along a 
portion thereof above the plate 152 and is provided with a stop comprising 
a nut 175, the position of which may be varied on the support rod to limit 
the amplitude of the vibratory movement of the filter element 27 to 
prevent distention of the bellows wall member 156. The stop 175 also 
engages the hub 168 to transfer a pressure lifting force acting on the 
filter element 27 directly to the bracket 166. The spring 172 is provided 
with a suitable force-deflection characteristic such that the bellows is 
normally in a neutral or relaxed position under the urging of the weight 
of the structure operably connected to the bellows and which would be 
supported by the bellows save the presence of the spring 172. 
The filter unit 150 is also adapted to function as a pressure relief valve 
and in this regard, the flange 160 is biased against the upper surface of 
the flange 126 by the coil springs 98 disposed around the respective 
assemblies of studs 129, retaining nuts 94 and washers 96. Tubular collars 
92 are also retained between each of the washers 96 and the upper surface 
of the flange 126, said collars extending through suitable clearance holes 
in the flange 160 and a gasket 181. 
The arrangement illustrated in FIG. 6 is adapted for applications wherein 
greater vibratory amplitude is desired in order to maintain the filter 
element substantially free of accumulations of particulate matter on the 
filter media. The vibrator 151 or a similar linearly reciprocable vibrator 
device is adapted to reciprocate the filter element vertically along the 
axis of the support rod 154. Moreover, the bellows type flexible wall 
member 156 is also able to withstand higher pressure differentials between 
the chamber 131 and the ambient atmosphere. If the pressure in the 
interior of the housing 118 should exceed the predetermined limit as set 
by the length of the tubular collars 92, the filter unit 150 including the 
flange 160, will lift off of the flange 126 to provide a flow passage 
between the faces of the flanges and the interposed gasket member 181. The 
flange 160 would normally not lift off the flange 126 until the nut 174 
engaged the hub 168 to thereby transfer a major portion of the lifting 
force directly to the flange 160. In applications where relatively high 
pressure differentials are experienced by the filter unit under normal 
operating conditions, the flexible wall member may be formed of the 
aforementioned metal bellows type structure, for example, in order to 
withstand the higher pressures without unwanted distention. 
Several embodiments of the invention have been described and those skilled 
in the art will recognize that various substitutions and modifications may 
be made to the specific arrangements shown and described without departing 
from the scope of the invention as recited in the appended claims.