Refrigerant suction line filter/filter-drier and method for the construction thereof

A combined filter and filter-drier, for the suction side of refrigeration and air conditioning systems, comprises a dual filter system straddling a cylindrical plug of dessicant. Upstream of the dessicant, a rigidly built primary filter assembly comprises an inlet deflector and a stepped filter. Downstream of the dessicant, a secondary filter assembly comprises an outlet filter pad which is compressed by a coaxially disposed spring near the inlet of the filter/filter-drier. The inlet deflector is preferably triangular in shape and is disposed transversely to the inlet. The stepped filter comprises a deflector filter pad, which preferably has the same shape but a smaller size than the inlet deflector, and a filter pad which is round, preferably is twice as thick as the deflector filter pad, and has a smaller diameter than the inside diameter of the filter/filter-drier, whereby an annular space is provided for swirling flow of an incoming vaporous mixture which thereby enters the peripheries of the stepped filter. In consequence, particles are gradually deposited throughout the interiors of the deflector filter pad and inlet filter pad so that pressure build up across the filter/filter-drier is also gradual and provides a warning of impending need for replacement. A method for constructing the filter-drier is also disclosed.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to filter-driers which are used in the suction line, 
between the evaporator and the compressor in a refrigeration or air 
conditioning system, for filtering and dehydrating the refrigerant and oil 
in their vapor states. 
2. Review of the Prior Art 
In air conditioning, refrigerating, heat pump, and hot gas defrost systems 
of the prior art, filters and driers are essential components for removing 
harmful contaminants and protecting the motor compressor, the heart of any 
such system, which is called upon today to withstand increasingly severe 
operational conditions because market conditions are requiring smaller and 
more compact systems and higher speed compressors which subject the unit 
to higher temperatures and pressures and tend to shorten its life and 
increase the danger of premature breakdown. 
Because the electrical portion of the motor is in direct contact with the 
refrigeration circuit, the chemical environment to which it is exposed is 
of prime importance. In addition, it is subject to damage from solids 
which must be prevented from reaching the compressor. These materials, in 
spite of utmost care in assembling and cleaning out a system, seem to be 
always present and are frequently not dislodged until the system is 
initially started up. They are major contributors to hermetic motor 
burn-outs and are also the cause of mechanical damage to close-tolerance 
parts by abrasive action. 
At the present time, a system sanitizing approach is used to isolate the 
motor compressor from three general categories of contaminants which play 
important roles in compressor failure. These are: (1) harmful soluble 
chemicals; (2) damaging liquids and solids; and (3) oxygen present in air 
as a non-condensable. 
Liquid line filter-driers are used to remove a broad spectrum of soluble 
contaminants, which include water, acids, oil breakdown products, tars, 
resins, gums, and dirt of relatively large particle size. The resins and 
gums are adsorbed, and the dirt is filtered out. Such receiver driers are 
described in U.S. Pat. No. 3,118,288 and U.S. Pat. No. 3,785,164. They 
generally include a desiccant, such as a molecular sieve or alumina, and a 
flow directing means for forcing the liquid to pass through the desiccant. 
A liquid line filter-drier for refrigeration systems is disclosed in U.S. 
Pat. No. 3,815,752 which combines an adsorbent bed and, downstream 
thereof, a pad of fiberglass within a conical or cylindrical wire form so 
that there is ample space within the enclosing shell for liquids to swirl 
around the fiberglass and enter it over a large area. However, the 
incoming liquid initially contacts a perforated plate containing the 
granular desiccant. 
Another spring-loaded filter-drier for the liquid side of refrigeration 
systems is taught in U.S. Pat. No. 3,841,490. It comprises an adsorbent 
bed within a perforated canister and a plurality of fiberglass pads within 
a cylindrical spring. The canister and pads are spaced peripherally from 
the enclosing shell, to provide an annular flow channel, but abut 
shoulders of the shell at each end thereof. Flow therefore passes through 
the inlet corners of the canister, then through the annular flow channel, 
and finally through the filter media. 
A bi-directional filter-drier for heat pump systems is additionally 
described in U.S. Pat. No. 4,125,469. This device comprises a cylindrical 
canister, which is peripherally spaced from the walls of the shell, and an 
outlet valve at each end, which is surrounded by an annular perforated 
screen which is closed against outward flow by a flap washer. Incoming 
flow moves through the flap valve, passes radially through the filter, and 
then moves axially through the hollow core of the filter to and through 
the outlet valve. 
However, vapor-phase filters having very little pressure drop are being 
increasingly used in recent years. Such vapor-phase filters are designed 
to remove harmful particles that are too small for filter-driers to take 
out in the liquid line, in addition to materials which are present in the 
system beyond the point where the liquid line filter-drier is installed. 
Used in conjunction with a liquid line filter-drier, a vapor-phase filter 
on the suction side of a system effectively isolates the motor compressor 
from finely divided steel and other metallic particles which are believed 
to be the major cause of motor burn-outs when carried to the windings by 
high-velocity suction gas. These offending particles include metal chips, 
solder flux, copper oxide, iron rust, carbon, corrosion solids, and the 
like which contribute to motor burn-out or cause compressor damage through 
abrasion. However, a suction-side filter will filter out gross quantities 
of the foreign materials as small as 5 microns (0.0002 inch) in diameter, 
with negligible pressure drop while permitting high rates of gas flow in 
the suction line. Such vapor-phase filters are necessarily large in volume 
as compared to liquid line filter-driers. 
Compressor damage is also caused by slugging of refrigerant and oils which 
typically occurs when a refrigeration or air conditioning system has been 
idle for an extended period. The suction effect of the compressor, when 
starting up after such idleness, creates such a low pressure that both 
liquid and vapor are pulled out of the evaporator and reach the compressor 
unless a means is provided for separating the liquid from the vapor and 
accumulating the liquid until it can be gradually reintroduced into the 
system as needed in the form of harmless droplets mixed with the vapor. 
Excessive quantities of liquid refrigerant dilute the oil, wash out 
bearings, and in some cases cause complete loss of oil in the crankcase of 
the compressor because of the high solubility of the oil in the 
refrigerant. Because compressors are designed to compress vapors, not 
liquids, such accumulations or "slugs" also can result in broken valve 
reeds, pistons, rods, crankshafts, and the like parts of a compressor. 
Thus, a storage component in the form of an uprightly disposed cylinder is 
commonly added to the suction side of the refrigeration or air 
conditioning system to act as a reservoir for temporarily holding the 
excess oil-refrigerant mixture and returning it at a rate that the 
compressor can safely handle. Such an accumulator usually can hold from 
about one-half to about two-thirds of the oil-refrigerant mixture that is 
within the system. 
However, in some refrigeration and air conditioning systems, accumulators 
are too small or are not installed even though needed. However, if a 
suction line filter-drier is added to the system, it will then be subject 
to the damaging effects of liquid slugs moving at a high velocity. 
Fiberglass, for example, can be literally torn and disrupted by such high 
velocity slugs. The surface of a fiberglass pad that receives the impact 
of fast-moving particles of metal and scale can also be rapidly plugged 
thereby. A need, therefore, exists to protect the relatively delicate 
fiberglass from impact of high-velocity particles and liquid slugs. 
It is, therefore, desirable to interpose a filtering medium between the 
evaporator and the compressor that can, at least, disperse such liquid 
slugs into smaller droplets which will be harmless to the compressor while 
simultaneously providing filtering benefits with respect to particles and 
drying benefits with respect to moisture. Furthermore, it has been found 
that any filter, liquid line or suction line, tends to become plugged 
rather rapidly and abruptly as particles build up on its surface. The 
pressure drop across the filter-drier therefore tends to build up abruptly 
and to cause the air conditioning or refrigerating unit to go out of 
service with little or no warning. A means for providing a gradual build 
up that would furnish preliminary warnings to maintenance personnel is 
consequently desirable. 
Designs of prior art filter-driers have generally sought to minimize 
inherent low efficiency with respect to pressure drop through the devices, 
because pressure drop in the suction line of a refrigeration or air 
conditioning system adversely affects the total system capacity and the 
cost of operation. In view of the limited space that is available adjacent 
to modern engines and refrigeration and air conditioning systems, both 
stationary and mobile, and the need for both filtering and drying, it is 
highly desirable to be able to combine the functions and the space 
requirements of a filter for very fine particles and the protective 
function of vapor state drying within the same device. 
SUMMARY OF THE INVENTION 
It is, therefore, an object of this invention to provide a device, for 
installation on the suction side of an air conditioning or refrigeration 
system, which is capable of filtering all fluids moving toward the 
compressor. 
It is another object to provide within this device a means for minimizing 
the coating of filtering surfaces with small particles that can blind the 
filter. 
It is additionally an object to provide a means for attenuating pressure 
drop caused by such coating of the filtering surfaces. 
It is further an object to provide a means for drying the filtered vapor. 
It is also an object to provide a means for protecting a filter within a 
filter/filter-drier from incoming high-velocity vapor, solid particles, 
and liquid slugs, and for disturbing such incoming materials into an 
upstream space providing access to both face and peripheral portions of a 
filter. 
In accordance with the principles of this invention and those objects, a 
low-pressure, suction line fliter/filter-drier for use in air conditioning 
and refrigerating systems is herein provided that comprises in sealed 
combination within an enclosing shell assembly, comprising a cylindrical 
shell having an interior diameter, a pair of closure members which are 
sealably attached to the shell, and inlet and outlet connectors which are 
sealably attached to the closure members, the following components: 
A. a desiccant, disposed as a cylindrical plug within the shell to provide 
an upstream space and a downstream space between the desiccant and the 
connectors; 
B. a dual filter system, comprising: (1) a primary filter assembly which is 
disposed within the upstream space, comprising: (a) a center spacer post 
having a pair of ends, (b) an inlet deflector which is fastened to one of 
the ends, (c) a stepped filter having a maximum diameter which is 
substantially less than the interior shell diameter, (d) a perforated 
filter pad support which is fastened to the other end of the spacer post 
and has substantially the same diameter as the interior shell diameter and 
is disposed downstream of the inlet deflector, whereby the stepped filter 
is selectively compressed between the deflector and the filter pad 
support; and (2) a secondary filter assembly which is disposed within the 
downstream space and has substantially the same diameter as the interior 
shell diameter, comprising: (a) a perforated support cup, (b) a screen, 
and (c) an outlet filter pad which is disposed between the support cup and 
the screen; 
C. an annular gasket, which is disposed adjacent to the filter pad support 
and on its downstream side, in peripheral contact with the interior 
diameter of the shell; 
D. a spring which is coaxially disposed within the shell between the inlet 
closure member and the inlet deflector, thereby compressing the dual 
filter system and the desiccant between the closure members. 
More specifically, the stepped filter comprises: 
A. A deflector filter pad having a smaller size in plan view than the inlet 
deflector; and 
B. an inlet filter pad having a substantially larger area in plan view than 
the area of the deflector filter pad, a circular shape in plan view, and 
the maximum diameter of the filter element. 
In addition, the deflector filter pad has a lesser thickness than the 
thickness of the inlet filter pad, most preferably approximately one-half 
the thickness of the inlet filter pad. It is also preferred that both the 
deflector and the deflector filter pad are triangular in shape. 
The annular inlet gasket preferably comprises: 
A. a highly compressed fiberglass filter pad which is disposed adjacent to 
the filter pad support and in surrounding relationship to the other end of 
the spacer post; and 
B. a perforated plate support which is disposed downstream of the inlet 
gasket and upstream of the desiccant. 
The invention further comprises a method of designing a filter/filter-drier 
to provide increased contaminant holding capacity therewithin and to 
enable pressure drop across the filter/filter-drier to increase gradually 
and provide a warning of impending need for replacement thereof, wherein 
the filter/filter-drier comprises a cylindrical shell, a pair of sealably 
attached closure members at the ends thereof, inlet and outlet openings in 
the closure members, and a primary filter assembly. Specifically, this 
method comprises: 
A. providing a stepped filter having a selected peripheral area, a selected 
facial area, and a selected internal volume which is accessible to a 
selected open upstream space that surrounds the filter and is in flow 
communication with the inlet opening; and 
B. providing, as another part of the filter assembly, a rigid deflector 
member which is disposed in coaxial alignment with the inlet opening, 
substantially downstream thereof, and transversely thereto for protecting 
the stepped filter pad; and 
C. providing a sealing means for isolating the open upstream space from the 
outlet opening except through a plurality of openings which are in flow 
communication with the stepped filter pad, whereby an incoming vaporous 
mixture enters the inlet opening, impinges upon the rigid deflector 
member, swirls through the upstream space, enters both the facial and 
peripheral areas of the stepped filter pad, moves along strata within the 
stepped filter, and deposits its solid particles at many locations 
therewithin before passing through the plurality of openings to the outlet 
opening. 
The filter/filter-drier of this invention comprises a compact, dual filter 
system straddling a desiccant. It comprises a primary filter assembly on 
the upstream side of the desiccant and a secondary filter assembly on the 
downstream side thereof. The desiccant and the secondary filter assembly 
are considered to be a filter-drier in combination, and the primary filter 
assembly is considered to be essentially a large-capacity filter as well 
as a dispersal means for slugs of liquid. The desiccant is formed in the 
shape of a cylindrical plug. 
The primary filter assembly comprises a stepped filter which is sized to 
provide clearance between it and the shell, thus allowing refrigerant to 
flow through an annular space surrounding the stepped filter and to enter 
through the periphery of the stepped filter and to flow in parallel to the 
layers of fibers while gradually filtering transversely thereto. This flow 
action allows contaminants to penetrate deeply into the stepped filter, 
thereby adding layers in depth to the filter area that is available in 
prior art filters and markedly increaing the filtration capacity of the 
stepped filter of the invention. Essentially, the entire volume of the 
stepped filter becomes available for capturing particles, instead of 
merely the pad surface in parallel to the fiberglass layers. 
The primary filter assembly comprises an inlet deflector, a deflector 
filter pad and an inlet filter pad forming the stepped filter, a filter 
pad support, and a center spacer post which controls the amount of 
compression of the filter pads and holds the components together as a 
rigid unit. The inlet deflector and the filter pad support are secured to 
the spacer post with the two filter pads compressed between them. 
The inlet deflector is a solid triangular metal part that prevents direct 
impingement upon the filter media by slugs or liquid and by solid 
particles. It deflects and reduces the velocity of the refrigerant, liquid 
slugs, and solid particles entering the vessel. The refrigerant is 
deflected into the annular space surrounding the stepped filter and 
affording access to the peripheries of the filter pads. The inlet gasket 
prevents bypassing of the filter element by the incoming refrigerant. 
The deflector filter pad, which is adjacent to the inlet deflector, is 
preferably similarly triangular in shape and nests against bent side lugs 
of the inlet deflector. This pad provides additional surface area for 
filtration, this additional surface area being entirely peripheral area, 
and further provides added space, longitudinally, between the secondary 
filter and the inlet connector, thereby increasing the flow capacity of 
the unit. The equilateral triangular shape of this pad also allows it to 
be produced without scrap between the pads that is inherent in the 
manufacture of round pads. 
Nevertheless, both the inlet deflector pad and the inlet deflector may be 
round or square. Preferably, the inlet deflector has side lugs, which 
partially but loosely enclose the deflector pad without restricting access 
of the swirling vapor to its sides, and pointed ends which may be bent as 
desired to provide snug centering within a fairly wide range of shell 
sizes. 
The inlet filter pad is round and has a substantially smaller diameter than 
the inside diameter of the shell. This allows the refrigerant entering the 
upstream space to flow into an annular space surrounding the inlet filter 
pad and then to enter this pad through its peripherary as well as through 
a portion of its face. Because the face tends to block or catch solid 
particles of all sizes, it also tends to become blocked fairly readily and 
at a uniform time. In contrast,, the periphery tends to allow the vapor as 
well as the solid particles to pass in parallel to the fibers for a 
considerable distance and to lodge therein in an uneven manner while 
working gradually through the layers toward the downstream outlet. In 
consequence, contaminants are distributed throughout the entire interior 
of the inlet filter pad, and the pressure drop thereacross rises quite 
gradually. 
The portion of the face that is covered by the inlet deflector pad receives 
inflowing material which has entered the periphery of the inlet deflector 
pad. It is consequently blocked much less readily and indeed functions as 
the interior of a one-piece stepped filter. 
The entire inlet filter assembly is spring loaded against the inlet gasket 
and thereby spring loads the desiccant bed. Such spring loading is 
accomplished by a conical spring which is installed between the inlet 
filter element and the inlet end of the shell. This inlet gasket is 
preferably an annular ring of fiberglass which is compressed between the 
cup-shaped filter pad support and a perforated plate which is adjacent to 
the desiccant bed. However, other prior art inlet gaskets, such as rubber, 
asbestos, or nylon, can be utilized. Moreover, these prior art gaskets may 
be secured to the perforated metal support cup with an adhesive, so that 
the perforated plate may thereby be omitted from the assembly. 
Downstream of the desiccant bed, the secondary filter assembly comprises an 
outlet filter pad which is housed in a perforated metal support cup that 
controls the amount of compression of the filter pad. This metal support 
cup rests against a screen and a perforated screen support. 
Refrigerant flows only through the face of the outlet filter pad. 
Therefore, the outlet filter pad picks up smaller particles, including 
fragments of fiberglass and of desiccant, than the inlet filter system. It 
also captures particles which have worked their way through the primary 
filter assembly and the desiccant bed. 
Although the filter/filter-drier of this invention is ideal for 
installation in the suction lines of refrigeration and air conditioning 
systems, immediately ahead of the compressors, it is also useful in the 
high-pressure liquid portions of such systems. Moreover, by utilizing the 
appropriate desiccants, this filter/filter-drier can additionally or 
alternatively be used in the high pressure vapor (hot gas discharge line) 
portions of such systems.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The filter/filter-drier 25 of this invention, preferably operating on the 
low-pressure side of a refrigeration or air conditioning circuit, 
comprises a shell assembly 30, a rigid primary filter assembly 40, an 
inlet gasket 53, a desiccant bed 61, and a secondary filter assembly. 
Shell assembly 30 comprises a cylinder 31, an inlet closure 33 which is 
welded to cylinder 31 at one end thereof, an outlet closure 35 which is 
welded to the other end of cylinder 31, a pair of connectors 37 which are 
sealably attached to inlet and outlet closures 33 and 35, and a valve 39 
which is sealably attached to inlet closure 33. Connectors 37 and valve 39 
furnish access to the interior of the shell formed by cylinder 31 and 
closures 33,35. 
Rigid filter assembly 40, as seen particularly in FIGS. 2-5, comprises an 
inlet deflector 41, a deflector filter pad 43, a spacer post 45, an inlet 
filter pad 47, and a filter pad support 49. 
Inlet deflector 41 is preferably triangular in shape and is also preferably 
somewhat larger than deflector filter pad 43, as seen most clearly in FIG. 
2. Deflector 41 comprises a top surface 71, side lugs 73, a center hole 
75, and corner lugs 77. Each corner lug 77 is of minimum size for its 
cylinder 31 and is formed simply by upwardly bending the unsupported 
corners of deflector 41 so that lugs 77 or, if necessary, the unbent 
points of these corners, touch the interior of cylinder 31, thereby 
bracing assembly 40 against sidewise movement. This means of emplacing 
assembly 40 enables it to fit snugly within a range of cylinder sizes, 
without requiring special devices for this purpose. 
Deflector filter pad 43 comprises a top surface 81, side surfaces 83, and a 
center hole 85. Center hole 85 is larger in diameter than hole 75 of 
deflector 41. Side surfaces 83 are loosely restricted by side lugs 73 of 
deflector 41 so that triangular pad 43 is maintained in its initial 
position. 
Inlet filter pad 47 comprises a top surface 91, a side surface 93, a center 
hole 89, and an edge 97 of contact by side surfaces 83, as seen in FIG. 4. 
Center hole 95 is of the same size as hole 85. The apexes of triangular 
pad 43 approximately touch the circumference of circular pad 47. In 
combination, pads 43,47 form a stepped filter pad providing many filtering 
advantages. 
Filter pad support 49 comprises a center hole 145, a side 147, perforations 
149, and edge 143 of contact by side surface 93. Center hole 145 is of the 
same diameter as hole 75 and permits entry by end surfaces 102 of spacer 
post 45. 
Spacer post 45 comprises recesses 101 in each end, end surfaces 102 before 
flaring thereof, flared ends 103 after flaring thereof, end shoulders 104 
which are adjacent to end surfaces 102, and a central surface 106 which is 
larger in diameter than end surfaces 102 and fits within holes 85,95. End 
surfaces 102 fit within holes 75,145. Spacer post 45 is of solid 
construction except for recesses 101. 
Inlet gasket 53 is preferably a 1/2-inch thick annular pad of fiberglass 
which, when compressed between filter pad support 49 and perforated plate 
support 55, forms a sealing gasket which engages the inner surface of 
cylinder 31, preventing passage of any solid particles therebetween. 
Compressed pad 53 encloses an annular empty space 51, between filter pad 
support 49 and perforated plate support 55, that surrounds the downstream 
end of spacer post 45. As an alternative, pad 53 can be constructed of 
nylon, rubber, asbestos, or like material which is cemented to the 
downstream peripheral surface of filter pad support 49 so as to engage the 
inner surface of cylinder 31 without need for compression by perforated 
plate support 55, so that support 55 can be omitted from the assembly of 
this filter/filter-drier. 
Desiccant bed 61 is preferably alumina but may comprise a molecular sieve, 
silica gel, Mobil Sorbead, or any other desiccant in ball or bead form. 
The secondary filter assembly comprises support cup 63, outlet filter pad 
65, screen 67, and screen support 69, as seen in FIG. 1. The dimensions of 
the sides of support cup 63, control the amount of compression of outlet 
filter pad 65 that is obtained. 
The filter/filter-drier of this invention is assembled by inserting the 
secondary filter assembly into the bottom of a cup formed by outlet 
closure 35 and cylinder 31, adding desiccant 61 on top of support cup 63, 
placing perforated plate support 55 on top of desiccant 61, putting 
annular pad 53 upon plate support 55, and positioning rigid filter 
assembly 40 on top of pad 53. Lastly, spring 59 is placed on top surface 
71 of inlet deflector 41, and inlet closure 33, fitted with its connector 
37 and valve 39, is pressed down against spring 59 and held securely while 
welding its edges to cylinder 31. 
The filtering function of rigid filter assembly 40 is heavily dependent on 
open space 58 that is available to the incoming vapors, liquid slugs, and 
solid particles entering inlet connector 37 and impinging upon surface 71. 
Although the periphery formed by surfaces 83, 93 can be extended by 
cutting them with a sinusoidal or jagged shape, for example, the benefit 
therefrom is less than the benefit of maintaining an adequate volume 58 in 
order to have maximum flow rate. If deflector pad 43 is much smaller than 
deflector 41, the additional volume that is available is not as useful as 
the filtering area that is given up thereby. Furthermore, problems with 
alignment of pad 43 and deflector 41 can develop because of such a 
disparity in size. If deflector 41 and pad 43 are larger than indicated in 
FIGS. 1-5, with very large lugs 77, open area 58 is significantly reduced 
and the flow rate is also reduced to a significant extent. 
Other combinations of shapes and sizes for the stepped filter of the 
invention than that shown in FIGS. 1-5 are possible. FIGS. 6-13 show a 
wide variety of such possible combinations. 
A round deflector filter pad 111 may be combined with a round inlet pad 
112, as seen in FIG. 6; a square deflector pad 114 may be combined with a 
round inlet pad 115, as seen in FIG. 7; and a triangular deflector pad 
117, of much smaller size than pad 43, may be combined with a round inlet 
pad 118 of normal size. 
The deflector filter pad and the inlet filter pad may also vary 
considerably in thickness, as seen in FIGS. 9-11. Deflector pad 121 has 
the same thickness as inlet pad 122 (FIG. 9); deflector pad 124 has 
greater thickness than inlet pad 125 (FIG. 10); and inlet pad 127 has less 
thickness than inlet pad 128 (FIG. 11). The relationship shown in FIG. 11 
is preferred. 
In addition, the sides of the deflector filter pad and the inlet filter pad 
need not be perpendicular to their faces. As seen in FIGS. 12 and 13, for 
example, pads 131, 132 may be truncated in shape, whereby the flow paths 
from various elevations along their peripheries to perforations 149 are 
more nearly uniform while still providing an annular space for travel of 
the inflowing vaporous mixture. 
Among the important capabilities of this filter/filter-drier, because it 
provides peripheral areas for entrance of vapors to be filtered, are the 
following: (1) the flow rate is greater and the pressure drop is less; (2) 
the vapors tend to move along the strata of the fiberglass and the solid 
particles which are to be filtered out tend to be caught at many locations 
instead of along a single surface zone as in prior art filters (a used 
deflector pad 43 and inlet pad 47 appear to be completely saturated with 
particles all over their interiors in addition to a thin surface zone 
along surface area 91 outside of lines 97 of pad 47); and (3) the pressure 
drop across assembly 40, as filter pads 43, 47 begin to fill up, rises 
gradually instead of sharply, as in prior art filters where the 
transversely disposed surface of a fiberglass pad or the cylindrical 
surface of a ceramic filter catches all of the filtered particles. 
Such a gradual buildup of pressure is very important when there has been a 
compressor failure, resulting in a burned out compressor and installation 
of a new compressor with hi-side and lo-side driers installed. As is well 
known in the art, after such an occurrence, it is practically impossible 
to remove all dirt and other solid particles from the system so that they 
have to be taken out by the filters. By having a filter/filter-drier of 
this invention on the low-pressure side of the system, it is feasible to 
watch the pressure gauge as the particles are filtered out and the 
pressure drop builds up and to replace the filter/filter-drier at a 
convenient time rather than being faced with a sudden pressure drop that 
renders the whole unit inoperative at an inopportune time. 
Because it will be readily apparent to those skilled in the refrigeration 
art that innumerable variations, modifications, applications, and 
extensions of the principles hereinbefore set forth can be made without 
departing from the principles and the scope of this invention, what is 
hereby defined as such scope and is desired to be protected should be 
measured and the invention should be limited, only by the following 
claims.