Visible restricted filter indicator

A filter indicator system for indicating when air flow through a filter is restricted includes an indicator mounted in a filter assembly downstream of the filter. The indicator includes a housing having a central space, a side wall, an end wall, an end inlet in the end wall, and a side outlet. A pop-up member is located in the central space and includes a signal portion which extends adjacent the end inlet. A moving device is then used for moving the pop-up member between a non-signalling position where the signal member does not extend noticeably through the end inlet and a signalling position where the signal portion extends noticeably through the end inlet. A pressure responsive releasing mechanism in the side outlet is associated with the pop-up member for initially holding the pop-up member in the non-signalling position and preventing movement by the moving device, and for subsequently releasing the pop-up member when the suction pressure in the side outlet drops below a predetermined value relative to an ambient air pressure present in the central space. The releasing mechanism includes: (a) a clearance between the signal portion and the end inlet to conduct ambient air pressure to the central space; (b) a seal member which is subject to the ambient air pressure on one side and the suction pressure on the other side; and (c) a biasing member for biasing the seal member against movement until a predetermined suction pressure is exceeded.

FIELD OF THE INVENTION 
The present invention relates generally to an indicator for restricted flow 
through a filter, and more particularly to a visible indicator for an air 
filter assembly which signals when flow through the air filter is 
undesirably restricted. 
BACKGROUND OF THE INVENTION 
It is difficult when using an apparatus with an air filter, for example an 
air compressor, to know when to change the air filter during operation 
because the apparatus or compressor unit has to be shut down in order to 
check the filter visually. In addition, when the filter is checked 
visually, it is often difficult to determine the amount of dirt already 
trapped by the filter and whether it is time to change the filter or 
filter cartridge. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, a filter indicator system is 
provided for indicating when air flow through a filter (or filter 
cartridge) is restricted. In general, the filter indicator system includes 
an indicator and a filter which is part of a filter assembly. The filter 
assembly includes a mounting wall and a means for positioning the filter 
in the filter assembly so that air in an inlet (upstream) portion of the 
filter assembly on one side of the filter (or filter wall) is drawn by a 
suction pressure through the filter to an intake (downstream) portion of 
the filter assembly on the other side of the filter (or filter wall). The 
filter assembly also includes a mounting aperture in the mounting wall 
which is downstream of the filter for mounting of the indicator. 
The indicator for signalling restricted flow of air through the air filter 
includes a housing. The housing includes a central space, a side wall 
adjacent the central space, an end wall adjacent the central space, an end 
inlet in the end wall., and a side outlet in the side wall. A mounting 
means is provided for mounting the end inlet of the housing to the 
mounting aperture in the mounting wall located downstream of the filter, 
whereby the housing is mounted inside the filter assembly with the housing 
exposed to the suction pressure in the filter assembly which moves air 
through the filter. A pop-up member is located in the central space of the 
housing and includes a signal portion which extends adjacent the end 
inlet. A moving means is then used for moving the pop-up member in the 
housing between a non-signalling position where the signal member does not 
extend noticeably through the end inlet and a signalling position where 
the signal portion extends noticeably through the end inlet and is easily 
viewed above the mounting wall. A pressure responsive releasing means in 
the side outlet is associated with the pop-up member for initially holding 
the pop-up member in the non-signalling position and preventing movement 
by the moving means and for subsequently releasing the pop-up member when 
the suction pressure in the side outlet drops below a predetermined value 
relative to an ambient air pressure outside of the filter assembly which 
is also present in the central space of the housing. 
In accordance with a preferred embodiment, the releasing means includes: 
(a) a clearance between the signal portion and the end inlet whereby the 
central space of the housing is subject to the ambient air pressure; (b) a 
seal means which fluidly restricts a flow of air from the central space of 
the housing to the side outlet such that the seal means is subject to the 
ambient air pressure on one side thereof and the suction pressure on the 
other side thereof; and (c) a biasing means for biasing the seal means 
against movement, the biasing means allowing a releasing movement of the 
seal means when the suction pressure drops below the predetermined value 
and a resetting movement of the seal means when the suction pressure rises 
above the predetermined value. In addition, the side outlet of the housing 
includes a side tube extending away from the side wall of the housing and 
fluidly connecting the central space of the housing with the suction 
pressure in the filter assembly. The pop-up member then includes a catch 
portion, and the seal means is a plug member such as a ball located in a 
cylindrical bore of the side tube adjacent the catch portion of the pop-up 
member when the pop-up member is in the non-signalling position so that 
the plug member is biased into engagement with the catch portion by the 
biasing means to prevent movement of the housing to the signalling 
position. 
In the preferred embodiment, the biasing means includes a spring, a cap 
member, a small aperture in the cap member, and a releasable attaching 
means for attaching the cap member to a free end of the side tube such 
that the spring and the ball are held in the cylindrical bore of the side 
tube by the end cap but are insertable and removable from the side tube 
upon removal of the end cap from the free end. In addition, the mounting 
means includes: (a) a mounting collar upstanding from the end wall which 
surrounds the end inlet and extends through the mounting aperture in the 
assembly wall of the filter assembly; (b) a locking collar which fits 
inside of the mounting collar and which has a central aperture through 
which the signalling portion extends and an outer flange extending away 
from the signalling portion and resting against the mounting wall; and (c) 
an attaching means for attaching the locking collar to the end wall of the 
housing so that the mounting wall is trapped between the outer flange of 
the locking collar and the end wall of the housing. 
Preferably, the housing is cylindrical and the central space is defined by 
a cylindrical wall. The pop-up member then includes a main body which is 
cylindrical and closely adjacent the cylindrical wall of the housing such 
that the main body is coaxially mounted for guided movement in the central 
space. The pop-up member also includes a catch portion in the main body 
which is engaged by the releasing means. Further, the signalling portion 
is cylindrical, coaxial with the main body, and extends from one end of 
the main body. 
More preferably, the housing includes an end opposite to the end wall and 
an opposite end aperture in the end. The moving means then includes a 
spring, a seal member and a releasable seal means for attaching the cap 
member in the opposite end aperture of the housing opposite to the end 
wall to seal the opposite end aperture. With this construction, the spring 
is held in the housing with the spring compressed against the pop-up 
member by the end cap but the spring and pop-up member are insertable and 
removable from the housing upon removal of the end cap from the opposite 
end of the housing. 
It is an advantage of the present invention that an indicator is provided 
which is inexpensively made and simple to install. 
It is also an advantage of the present invention that the disclosed 
indicator is inexpensive to produce and easily viewed to determine when a 
filter in use has restricted air flow therethrough to the point where the 
filter should be replaced. 
It is a further advantage of the present invention that the indicator can 
be reset and used in association with a new filter once the clogged filter 
has been replaced. 
It is still another advantage of the present invention that the indicator 
is made primarily of simple and inexpensive plastic and/or metal parts and 
can be used in any orientation. 
Other features and advantages of the present invention are stated in or 
apparent from detailed descriptions of presently preferred embodiments of 
the invention found hereinbelow.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
With reference now to the drawings in which like numerals represent like 
elements throughout the views, a filter indicator system 10 is depicted in 
FIG. 1 for use with an air compressor (not shown). Filter indicator system 
10 is used for indicating when air flow through a filter assembly 11 
including a cylindrical filter 12 has been restricted above a certain 
amount, typically due to the clogging of air filter 12 with dirt or the 
like. As shown, filter 12 is suitably positioned in filter assembly 11 by 
a suitable means such as threadably engaged holding plate 13 so that 
filter assembly 11 is divided by cylindrical filter 12 into an inlet or 
upstream portion 20 outside of filter 12 and an intake or downstream 
portion 22 inside of filter 12 according to the air flow (depicted 
schematically by the arrows). This air flow is caused by the compressor or 
the like to which filter assembly 11 is threadably attached by mounting 
tube 16 extending from holding plate 13 as well known in the art. As air 
is drawn through filter 12, it will be appreciated that a suction pressure 
exists in intake portion 22, and that this suction pressure increases 
(actual pressure drops) as filter 12 becomes clogged and air flow through 
filter 12 decreases. It will also be appreciated that outside of filter 
assembly 11 there is an ambient air pressure. Provided at any suitable 
location in a mounting wall 14 of filter assembly 11 is a mounting 
aperture 24. 
Mounted in mounting aperture 24 by a mounting means 18 is an indicator 26 
which is depicted in detail in FIGS. 2-4. It will be appreciated that 
filter assembly 11 and hence indicator 26 can be oriented in any direction 
besides that depicted, and the position of mounting aperture 24 by 
mounting wall 14 is selected for convenience. Indicator 26 includes a 
hollow plastic housing 28 which is preferably cylindrical. A central space 
30 is provided in housing 28 which is defined by an inner cylindrical wall 
32. Housing 28 also includes an end wall 34 adjacent central space 30 with 
an end inlet 36 therein, as well as an end 38 also adjacent central space 
30 and opposite to end wall 34 with an opposite end aperture 40 therein. 
Extending between end wall 34 and opposite end 38 is a side wall 42 
adjacent central space 30 with a side outlet 44 therein. Preferably, side 
outlet 44 is formed by a side tube 46 extending away from side wall 42. 
Side tube 46 includes a free end 48 and a cylindrical bore 50 therein 
which connects intake portion 22 with central space 30. 
As noted above, housing 28 is mounted in mounting wall 14 of filter 
assembly 11 by a mounting means 18. Mounting means 18 includes a mounting 
collar 52 upstanding from end wall 34. Mounting collar 52 surrounds and 
extends end inlet 36 up through mounting wall 14 as shown in FIGS. 2 and 
3. Located above and in mounting collar 52 is a plastic locking collar 54. 
As shown, locking collar 54 includes an outer flange 56 which extends 
along mounting wall 14 so that mounting wall 14 is trapped between outer 
flange 56 and end wall 34. Locking collar 54 also includes a central 
aperture 58 which is defined by a split leg portion 60. An attaching means 
62 attaches locking collar 54 to end wall 34 with mounting wall 14 trapped 
therebetween. Attaching means 62 is conveniently a catch lip 64 formed on 
the outside of leg portion 60, with leg portion 60 coming to a point and 
being split to facilitate insertion of locking collar 54 in end inlet 36 
of end wall 34. Obviously, other suitable attaching means are possible as 
well known in the art, such as a threaded engagement or opposed teeth 
which would afford the capability to trap different sizes of mounting wall 
14. Still other attaching means are also possible, including other twisted 
engagement mechanisms, other snap locking mechanisms, screws or the like. 
Provided in central space 30 of housing 28 is a plastic pop-up member 66. 
Pop-up member 66 includes a main cylindrical body 68 which is sized to fit 
closely adjacent but spaced from cylindrical wall 32 of housing 28 so that 
pop-up member 66 is thereby mounted for coaxial guided movement in 
cylindrical central space 30 of housing 28. Provided in main body 68 is a 
catch portion 70, which is conveniently formed as a semicircular groove. 
Extending away from an end of main body 66 and up through end inlet 36 is 
a cylindrical signalling portion 72. It will be appreciated that 
signalling portion 72 extends as well through central aperture 58 of 
locking collar 54 with a small clearance therebetween so that central 
space 30 of housing 28 is substantially at the ambient atmospheric 
pressure existing outside of filter assembly 11. 
In order to move pop-up member from a non-signalling position as depicted 
in FIG. 2 to a signalling position as depicted in FIG. 3, a moving means 
74 is provided. It will be appreciated that in the non-signalling 
position, the free end of signalling portion 72 is substantially flush 
with the outer surface of outer flange 56 of locking collar 54; while in 
the signalling position of FIG. 3, the free end of signalling portion 72 
extends substantially above locking collar 54. If desired, signalling 
portion 72 is suitably colored or marked to make it easier to see or 
notice when signalling portion 72 is in the signalling position. Moving 
means 74 includes a spring 76 which is compressed between end 38 of 
housing 28 and main body 68 of pop-up member 66. 
Conveniently, pop-up member 66 and spring 76 are loaded into housing 28 
through opposite end aperture 40 provided in end 38. To accomplish this, 
moving means 74 includes a plastic seal member 78 which sealingly closes 
opposite end aperture 40 to maintain the ambient pressure in central space 
30. Seal member 78 is releasably held in place in opposite end aperture 40 
by a suitable releasable seal means 80. Conveniently, releasable seal 
means 80 is similar to attaching means 60 and includes a split catch lip 
81 which resiliently holds seal member 78 onto end 38 as shown. Obviously, 
other releasable seal means are also possible as well known to those of 
ordinary skill in the art. 
Indicator 26 also includes a pressure responsive releasing means 82 located 
in side outlet 44. Releasing means 82 is used to initially hold pop-up 
member 66 in the non-signalling position and thereby to prevent movement 
of pop-up member 66 by moving means 74. In other words, releasing means 82 
holds pop-up member 66 against the moving force or bias exerted by 
compressed spring 76. Then, when the suction pressure in intake portion 22 
drops below a predetermined value, for example to a value where the 
suction pressure increase corresponds to a pressure drop across filter 12 
of 5%, releasing means 82 releases pop-up member 66 so that moving means 
74 by action of spring 76 moves pop-up member 66 from the non-signalling 
position to the signalling position. 
In this preferred embodiment, releasing means 82 includes a seal means or 
pressure responsive member 84. Seal means 84 is preferably a plug member 
such as a round steel ball 86 which is located in bore 50 of side tube 46. 
Ball 86 is sized to fit movably in bore 50, but to substantially fill bore 
50. Ball 50 is also sized to fit into catch portion 70 of pop-up member 66 
when pop-up member 66 is in the non-signalling position. With ball 86 in 
place, it will be appreciated that ball 86 is subject to ambient air 
pressure on the side which faces central space 30 of housing 28 and to the 
suction pressure of intake portion 22 on the other side. Normally, ball 86 
is held in place in catch portion 70 of pop-up member 66 by the resilient 
force of a biasing means 88. In the engaged position with catch portion 
70, it will be appreciated that ball 86 prevents pop-up member from moving 
from the non-signalling position to the signalling position. 
The holding force of biasing means 88 is sufficient to hold ball 86 in 
position despite the designed pressure difference between ambient air 
pressure in central space 30 and the suction pressure in intake portion 
22. However, when filter 12 becomes sufficiently clogged and the suction 
pressure in intake portion 22 increases (drops), biasing means 88 is 
designed to give way to the increased pressure differential across ball 86 
due to the increased suction pressure and thus to allow a releasing 
movement of ball 86 from catch portion 70. It will also be appreciated 
that after filter 12 is replaced, biasing means 88 also provides a bias to 
move ball 86 back into engagement with catch portion 70 when signal 
portion 72 is pushed back into housing 28 to reset indicator 26. 
Biasing means 88 preferably includes a spring 90 and a plastic cap member 
92 with a small aperture 94 therein. Small aperture 94 in cap member 92 
assures that the suction pressure present in intake portion 22 is also 
present on the associated side of ball 86. Conveniently, cap member 92 
held on free end 48 of side tube 46 by a releasable attaching means 96. 
Releasable attaching means 96 is formed by opposed arms 98 which catch on 
an outer lip 100 of free end 48 as shown. 
In use, filter indicator system 10 requires that mounting aperture 24 first 
be provided (by design or with a drill or the like) in wall 14 at a 
position which is easily viewed and accessible from inside and outside of 
filter assembly 11. Once mounting aperture 24 is present, and indicator 26 
is otherwise assembled except for locking collar 54, mounting collar 52 of 
housing 28 is passed from inside of filter assembly 11 through mounting 
aperture 24 in mounting wall 14. While indicator 26 is thus held in place, 
locking collar 54 is inserted through mounting wall 14 from outside of 
filter assembly 11 around signalling portion 72 of pop-up member 66 and 
inside of mounting collar 52 until catch lip 64 of locking collar 54 
engages underneath of mounting collar 52. It will be appreciated that as 
both mounting collar 52 and locking Collar 54 are formed of a suitable 
resilient plastic material, the clearance between locking collar 54 and 
signalling portion 72 allows the insertion of locking collar 54 into 
mounting collar 52 and the locking of catch lip 64 after insertion. Once 
catch lip 64 catches below mounting collar 52, mounting wall 14 is snugly 
trapped between outer flange 56 of locking collar 54 and end wall 34 of 
housing 28; and indicator 26 is thus securely mounted inside of filter 
assembly 11. Obviously, for different thicknesses of mounting wall 14 both 
locking collar 54 and mounting collar 52 would have different heights. 
Demounting of indicator 26 is also possible either by breaking of locking 
collar 54 from outside of filter assembly 11 or pinching together of catch 
lip 64 (after removal of pop-up member 68 as discussed subsequently) from 
inside of filter assembly 11. 
In operation, whenever a suction pressure is present in intake portion 22 
of filter assembly 11, the suction pressure is also present on the 
associated side of ball 86 in side tube 46 by virtue of aperture 94 in cap 
member 92. As ball 86 substantially fills bore 50, ball 86 thus 
essentially seals bore 50 so that the other side of ball 86 is subject to 
the ambient air pressure from outside of filter assembly 11 which is 
transmitted into central space 30 via the clearance between signalling 
portion 72 and central aperture 58 in locking collar 54. Actually, some 
leakage about ball 86 will occur as ball 86 is mounted to allow axial 
movement in bore 50, but this leakage will be minor and easily compensated 
for (as noted subsequently). With the ambient air pressure on one side and 
the suction pressure on the other side, ball 86 is urged toward the 
suction pressure by the pressure differential across ball 86. Spring 90 in 
side tube 46 serves to counter this pressure differential so long as the 
suction pressure is above a predetermined value (or a predetermined value 
which has been compensated for by the expected leakage around ball 86). 
The predetermined value is selected as some value which is achieved when 
filter 12 becomes sufficiently clogged and replacement or cleaning is 
desirable. 
When the predetermined value of suction pressure is reached or exceeded, 
the counter force offered by spring 90 is insufficient to counter the 
moving force of the pressure differential across ball 86. Ball 86 thus 
moves away from catch portion 70 of pop-up member 66 so that pop-up member 
66 is no longer held in the non-signalling position. Thus, under action of 
spring 76, pop-up member 66 is moved toward end wall 34 and signalling 
portion 72 extends substantially beyond end inlet 36 and locking collar 54 
to be easily viewed and serve as an indication that it is time to change 
filter 12. 
After indicator 26 has signalled that filter 12 should be replaced by the 
extending of signalling portion 72 above end inlet 36 and filter 12 has 
been replaced, it will be appreciated that indicator 26 is easily reset to 
perform the same function again. This is accomplished simply by manually 
pushing down on the extended signalling portion 72. Initially, this causes 
ball 86, which is urged into engagement with the surface of the adjacent 
portion of main body 68 but which is still trapped in bore 50 by this 
engagement, to be pushed back into bore 50 as ball 86 rides along this 
surface. Thus, by pushing down until the free end of signalling portion 72 
is flush with outer flange 56 of locking collar 54, main body 68 of pop-up 
member 66 is returned to the position where ball 86 is urged into catch 
portion 70 by spring 90. As the suction pressure in intake portion 22 is 
now above the predetermined value (by virtue of the new filter not causing 
a suction pressure below the predetermined value or the suction pressure 
not being exerted while filter assembly 11 is removed from the compressor 
and filter 12 is replaced), ball 86 thus holds pop-up member 66 in the 
non-signalling position once signalling portion 72 is manually released. 
Whether mounted in filter assembly 11 or not, the various parts of 
indicator 26 are capable of being removed and maintained/cleaned or 
replaced as required. Preferably, this is accomplished by first removing 
cap member 92 by suitably pulling on cap member 92 to allow access to bore 
50. Once cap member 92 is removed, both spring 90 and ball 86 can be 
removed. With cap member 92 removed, the biasing force of spring 90 is 
taken off of ball 86 so that pop-up member 68 can also be removed. Pop-up 
member 68 is removed by first pulling seal member 78 from end 38 of 
housing 28. This allows access to central space 30, and the easy removal 
of spring 76 and pop-up member 68. Reassembly preferably occurs in the 
reverse order. 
While the present invention has been described with respect to exemplary 
embodiments thereof, it will be understood by those of ordinary skill in 
the art that variations and modifications can be effected within the scope 
and spirit of the invention.