Note: Descriptions are shown in the official language in which they were submitted.
~78347 :, .
COMPRESSED AIR FILTER ASSEMBLY
Background of the Invention
.
Heretofore, as shown in Frantz patent No. 3,~90,122,
issued June 17, 1975, filter units in compressed air systems
have passed air to a reservoir usually through an outlet
check valve or sometimes through an unvalved outlet line, the
latter if the unit is open to atmosphere only briefly during
the compressor's idling cycle. In either case, the objective
is to prevent the reservoir from losing pressure through the
filter unit when the compressor is not pumping. Unless the
ambient air is exceptionally dry or the filter unit contains
a desiccant, the air will be saturated or even super-saturated
with moisture on both entering and leaving the unit, although
the outgolng air will have a lcwer absolute moisture content,
if, as in the Frantz patent, the filter unit is adapted to
remove moisture other than by adsorption.
The problem posed by a filter unit of the non-desi-
... .
ccant type in passing at least saturated air to a reservoir,
whether through a check valve or an unvalved outlet, is that
the resistance to flow is substantially or entirely the back
pressure from the reservoir. In turn, the compressor, through
a governor, is responsive in its pumping and idling cycles
to reservoir pressure, idling when the reservoir reaches a
predetermined maximum or cu~out pressure and beginning to
pump at a predetermined minimum or cut-in reservoir pressure
and continuing to pump until the pressure in the reservoir
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~3i78347
is again at maximum. Thus, during the pumping cycle, the
saturated air passing from the filter unit will range in
pressure from at or slightly above the minimum to the maximum ~-
reservoir pressure. The absolute moisture content of satur-
ated air decreasing with increasing pressure, the inevitable
result is that, when the reservoir is fully charged to its
maximum pressure, the air in the reservoir will be super-
saturated, to the detriment of air brakes or other equip-
ment operated by reservoir pressure. It is with a solution `
of this problem that the present invention is primarily
concerned.
Summary of the- Invention
.
The primary object of the present invention is to
provide an improved compressed air filter assembly whereby
super-saturation of the air with which a reservoir is charged
through the assembly is made avoidable by combining filter
means depending on cooling for removing moisture from the air
with outlet pressure regulator valve means adjustable to pre-
determine the pressure at which air is passed from the filter `
means to the reservoir.
Another object of the invention is to provide acompressed air filter assembly adapted by centrifugal action
to cool and separate moisture and other contaminants from
compressed air and not only regulated in the pressure at which -
it can pass air to a reservoir but protected by a normally
open inlet valve automatically closing at the end of the
compressor's pumping cycle from receiving and being heated by
hot air from the compressor during the compressor's idling
cycle. i-
~078347
An additional object of the invention is to provide
a compressed air filter assembly having, as outlet valving for
a filter unit, a pressure regulator valve finely adjustable
to open within a predetermined narrow pressure range and only
in response to pressure in the filter unit, for preventing
the unit from passing filtered air to a reservoir except when
the air in the unit is at substantially maximum reservoir
or other predetermined pressure.
A further object of the invention is to provide
a compressed air filter assembly having a filter unit for
centrifugally cooling and separating moisture and other con-
taminants from compressed air from a compressor, wherein the
effectiveness of the assembly in cooling is increased by admit-
ting air through inlet valving only during the compressor's
pumping cycle and leading the air from the inlet valving `
to the filter unit through a preliminary centrifugal cooling
unit surmounting and heat-insulated from the filter unit and
mounting the inlet valving.
Another object of the invention is to provide a
compressed air filter assembly, wherein a filter unit opera-
tive during a compressor's pumping cycle for separating con-
taminants from compressed air, drains contaminants through a
normally closed, then open drain valve during the compressor's
idling cycle and has capacity for storing during the pumping
cycle sufficient air to purge the unit during draining of any
collected or entrapped contaminants.
Other objects and features of the invention will
appear hereinafter in the detailed description, be particularly ~
pointed out in the appended claims and be illustrated in the ~-
accompanying drawings, in which:
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1 ~7834~
Figure Description :.
Figure 1 is a view of a preferred embodiment of the
improved compressed air filter assembly of the present inven~
tion and the associated components with which it usually is
installed, the assembly being shown in central vertical section -
and the components schematically;
Figure 2 is a view on the section of Figure 1 and
an enlarged scale of ~he outlet pressure regulator valve
removed from the remainder of the assembly; and
Figure 3 is an end elevational view taken along
lines 3-3 of Figure 2,
Detailed Description
~:.
Referring now in detail to the drawings in which like
reference characters designate like parts, the improved com- .
pressed air assembly of the present invention, while adapted
for use in other compressed air systems in which super-saturated ...
reservoir air can adversely affect the operating characteristics ;
or service life of air-operated equipment, in its preferred ,~
embodiment is particularly designed for use in compressed air
systems of vehicles, such as trucks, buses and rapid transit
cars/ and will be so described as exemplary of the invention.
As indicated schematically in Figure 1, the improved
filter assembly, designated as 1, is designed to be installed
in a compressed air system between a compressor and a reservoir.
The assembly 1 is comprised of a filter unit 2 having a hous-
ing 3 in which contaminants are separated from compressed
air received from or supplied by the compressor before being
passed as filtered air to the reservoir, an inlet valve 4 and an
.. .
1~783~
:
outlet pressure regulator valve S on opposite or inlet and
outlet sides of the housing, an initial or preliminary cooling
unit 6 surmounting and heat-insulated from the housing and ;~
suitably mounting the inlet valve, and a drain valve 7 prefer-
ably mounted on and suspended from the bottom of the housing. i
Conventionally, the compressor, under control of
a governor, alternates between pumping and idling cycles in
response to predetermined minimum or cut-in and maximum or
cut-out pressures in the reservoir, pumping whenever the reser-
voir pressure is between minimum and maximum and idling while --
the pressure is at maximum. The preferred filter unit 2, in
turn, responds automatically to the condition of the compressor,
cooling and separating contaminants from the compressed air
during the pumping cycle and draining the separated contami-
nants through the drain valve 7 during the idling cycle.
Upright and generally cylindrical, the housing 3
is divided vertically into an externally finned upper part 8
and a lower part 9 removably attached, as by bolting, to the
upper part. A suitably cylindrical central bore 10 in the upper
part 8 slidably receives or seats a correspondingly cylindri-
cal canister or cartridge 11 having at the bottom a removable
foraminous cap or cover 12 resting or supported on internal
vertical ribs 13 in and instanding radially from the side of
the lower part 9. The canister 11 is laterally or radially
spaced from the housing's upper part 8 by a continuous heli-
cal rib or baffle 14, conveniently integral or rigid with and
instanding from the housing 3 and defining with confronting
sides or surfaces of the housing and canister a downwardly ;
~78347
directed or extending helical air passage 15. Leading from
an inlet passage 16 in the upper portion of the housing 3,
through which hot, dirty air is introduced or injected during
the compressor's pumping cycle, to a sump 17 in the lower part
or bottom bowl 9, the helical passage 15 causes or forces the
injected air to flow cyclonically downwardly therethrough,
in process centrifugally cooling the gas and separating heavier
contaminants therefrom.
The canister 11 has in its upper end a central out-
let or opening 18 opening onto an outlet passage 19 in the ~ :
upper end portion of the housing 3 and, therethrough, to the
housing's outlet port 20 and the outlet pressure regulator
valve 5. Suitably sealed against the housing 3 about the out- -
let 18 for blocking the injected air in the inlet passage ;
16 from bypassing the helical passage 15, the canister 11 prefer-
ably contains or encloses in its upper end portion a filter
element 21, which most suitably is a scrubber having around ~
a central tube 22 of a foraminous-topped, open-bottomed cas- ~:
ing or container 23, a pad 24 of stainless steel wool for
entrapping or physically filtering oil droplets or like parti-
cles not previously removed from the air. With its casing 23
press-fitted or otherwise suitably fixed in position in the
.canister 11 and a relief valve 25 in its central tube 22 for
bypassing the pad 24 in case the latter becomes clogged, the :;
scrubber 21, by downwardly extending and externally threading
the extended part of the tube to receive a nut 26, is enabled
to mount or suspend therebelow within the canister 11 an ~ ;
inner canister or shell 27. Open at the bottom but closed
~` ~078347
at the top except in registry with the central tube 22, the
inner canister 27 is spaced at the side radially or laterally
inwardly from the confronting side of the outer or main canis-
ter 11 to form between confronting sides thereof a vertically
extending annular passage 28 for passing air from the sump 17
to the scrubber 21. Of much larger volume than the relative-
'y narrow passages 15 and 28, the open-bottomed hollow interior `~
of the inner canister 27 serves as a storage chamber 29 of
relatively large capacity for storing during the compressor's
pumping cycle compressed air for powering the draining or `~
discharge of separated or filtered contaminants when the drain ;
valve 7 next opens.
The automatic response of the filter assembly 1 to
the condition of the compressor in filtering during the pump-
ir.g cycle and draining during the idling cycle, is the function
or result of the combined or concerted action of the inlet
valve 4 and drain valve 7. In terms of either the pumping
cycle of the compressor or their own unactuated conditions,
the inlet valve 4 is normally open and the drain valve 7
normally closed. If, as preferred the valves are actuated by
air rather than electrically, each suitably will have as its
valve member a differential piston 30 spring-held or pressed
in normal position and shiftable to its alternate position by ;
actuating air applied to the piston's large head 31. For
simultaneous actuation out of or back to normal position or
condition, in synchronism with a cycle change of the compres-
sor, the compressed air for both of the valves 4 and 7 suitably
is air diverted to and circulating in the system's governor r
line when the compressor is caused by the governor to idle,
`` 1~9783~7
;: ..
the actuating air conveniently being applied simultaneously
to both valves through connecting piping 32.
Connected to the sump 17 through a drain port 33 in
the bottom of the housing 3, the preferred drain valve 7 has ~:
on its piston 30 a single, normally seated, small head or valve
element 34. When used with a compressor equipped with an
aftercooler, the inlet valve 4 also should be a single-seated :
valve, with a single, normally unseated, small head or valve
element 35 seated during the idling cycle for blocking both
dumping of the aftercooler and flow of hot, low pressure air
into the filter unit 2. However, for compressors not having
aftercoolers, the preferred inlet valve 4 is double-seated,
with a second small head 36 spaced from the first head 35 and
alternately seatable for normally closing a downwardly directed
exhaust port 37 in the bottom of the valve through which hot
air from the ldling compressor is exhausted to atmosphere and -
its heat dissipated.
Whether or not the associated compressor is equipped :
with an aftercooler, the filter assembly l, for increasin~ its
effectiveness in cooling the hot dirty air received from the
compressor during the latter's pumping cycle and removing mois-
ture therefrom by condensation, preferably includes for addi-
tional cooling capacity the preliminary, initial or pilot cool-
ing unit 6. Interposed between the filter unit 2 and inlet
valve 4 to act on the injected air at the latter's highest temp-
erature, the cooling unit 6 desirably surmounts or is
mounted on the top of the filter unit 2 and heat-insulated
therefrom by an intervening, thermally insulating gasket 38.
Releasably attached to the filter unit 2, as by a connecting or
_g _
~783~7
mounting bolt 39 centered on the housing 3 and extending
upwardly through and fluid-sealed within the top wall 40
thereof, the preliminary or auxiliary cooling unit 6 in turn
conveniently mounts the inlet valve 4. As does the filter
unit 2 in the helical passage lS, the preferred cooling unit 6
depends on centrifugal cooling from cyclonic or vortical flow
induced from the compressed air's own impetus or kinetic energy,
for partly cooling the hot, dirty air from the compressor
during the pumping cycle before the air is passed or admitted
to the cooling unit. For the purpose, the preferred cooling
unit 6 has an upwardly opening central cavity 41 surrounded
by an annular or generally cylindrical side wall 42 of the
unit's substantially cup-shaped body 43. At one side the
cooling unit has an inlet port 44 opening outwardly onto the
inlet valve 4 and inwardly onto the inlet end of a suitably
one or uni-level, single coil or loop, spiral passage 45, whose
outlet end opens through an axially ported or apertured plug 46
connecting the body 43 and housing 3, onto the housing's inlet
passage 16. Heat from the air passing through the cooling
unit 6 is dissipated to ambient air partly through the inside
of the side wall 42 and the area exposed at the bottom of the
body 43, but mainly through external fins 47 on the body's top
and sides.
Although the primary function of the cooling unit 6
is to partly cool the air from the compressor in advance of
the filter unit 2, there will usually be some condensation of
moisture and separation of heavier contaminants incident to
the centrifugal cooling. With the ported plug 46 at a low ~
point of the spiral passage 45, any such separated moisture and ~ -
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1C~78347
other contaminants will flow downwardly through the plug and
inlet passage 16 to the helical passage 15 in the filter unit
2 in which the assembly l performs or conducts its main or
principal stage of centrifugally cooling and separating or
filtering condensed moisture and other contaminants from the
initially hot, dirty air received when the compressor is
pumping. On passing from the helical passage lS, the separated
contaminants will collect in the sump 17, while the now
relatively cool and clean air will have its cyclonic flow
broken up or interrupted by the internal vertical ribs 13 and,
reversed in direction, flow upwardly with some further cooling
through the annular passage 28 around the inner canister 27
to the scrubber 21 for filtering or removal by entrapment
of remaining oil droplets or like particles. With the assem-
bly's cooling and cleaning or filtering now completed, the
cool, clean air, on reaching the outlet port 20, will be at
a temperature approximating ambient and reduced in absolute
moisture content to saturation at the temperature and pressure
prevailing in that part of the housing 3.
Were the outlet valving of the assembly l a conven-
tional check valve, backflow of air from the reservoir to the
filter unit 2 would be blocked during the compressor's idling -
cycle, but the valving would open to pass air to the reservoir
during the pumping cycle at a pressure only slightly higher
than the reservoir's minimum pressure. The outlet pressure
regulator valve 5 of this invention does act as a check valve
during the idling cycle in blocking backflow of air from the
compressor, but, by contrast with conventional outlet valving,
it also is adapted to prevent flow of cool filtered air to the
reservoir during the pumping cycle until and unless the air in
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1CJ 7~347
the filter unit 2 is at a predetermined pressure which prefer-
ably is the reservoir's maximum.
The preferred outlet pressure regulator valve 5 has ;
a two-part body 48 formed of a base or main part 49 and cap or
outer part 50, with an axial, mainly cylindrical bore 51extend-
ing therethrough. Externally generally cylindrical, the body
48 is attached to a side of the housing 3, as by bolting
through a wing flange 52 integral with the base 49. When
attached, the body 48 covers the outlet port 20 of the
housing 3 and has an inlet 53 at the inner end of the axial
bore 51 open to and aligned with the outlet port and is suitably
gasketed for sealing between itself and the housing about
its own inlet and the housing's outlet port. The cap 50
is screwed into the outer end of the base 49 and, for that
purpose, conven~ently has between its ends an integral, hex- ;
sided, radially outstanding, annular boss 54, which also serves
as a stop to limit the cap's penetration into the base.
Outwardly of the inlet 53, the axial through-bore
51 is divided axially or longitudinally intermediate its
ends into adjoining or contiguous, smooth-walled valve and
sprlng chambers or compartments 55 and 56, respectively, the r
former in the base 49 and the latter in the cap 50. The valve's
valve element, in the form of a shuttle or floating piston
57, is slidable or shiftable axially or longitudinally in the
valve chamber 55 between the closed and open positions shown ~;
in Fig. 2 in solid and dot-and-dash lines, respectively. Shift-
ing in opening under force of air pressure in the inlet 53
against the yieldable resistance of a preferably coil return
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1~78347
spring 58, the shuttle 57 in open position connects the inlet
through an annular groove or channel 59 surrounding or encircl- ~
ing the valve chamber 55, to a side or bottom outlet 60 in the ~:
base 49 and thence, through suitable piping, to the reservoir, ;
as shown schematically in Fig. 1. For sealing against leakage --
past the shuttle 57 in either of its positions, the shuttle is
sealingly engaged by the outer and alternately engaged and
disengaged by the inner of a pair of longitudinally or axially `~
spaced O-rings 61 seated in the base49 about the valve chamber
. . .
55, with the inner held in place by an end-notched nut 62 and the ~-
outer by the cap 50 and an interposed bushing 63.
In yieldably resisting opening movement of the shut-
tle 57, the return spring 58 seats at opposite ends against
and acts between an annular flange or head 64, integral with j~
and radially outstanding from the outer end portion of the ~ .
shuttle in the spring chamber 56 and a reactance in the form ; .
of a spring follower 65. In and adjustably, variably or sel-
ectively positionable, axially or longitudinally of the spring .
chamber 56, the spring follower 65, inside the spring 58, has
or carries, as a fixed or integral lnner part, a suitably frus-
to-conical, inwardly tapered spacer or stop 66. Projecting
inwardly toward and normally spaced from but engageable with .
an outwardly projecting abutment 67 on the outer end of and
integral with the shuttle 57, the spacer 66, for any position
of the~follower, determines the limits of the outward move- -
ment of and compression of the spring 58 by the shuttle 57, the
inward limit of movement of which is fixed by engagement of
the flange 64 with the bushing 63.
For adjusting the position of the spring follower 65, .
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1~78347
, ' '
the outer end portion of the axial bore 51 is threaded for
receiving an adjusting screw 68, suitably having a ball-shaped
inner end 69 seating in a conical socket 70 in the outer or con-
fronting end of the follower. With the spring 58 acting
outwardly on the spring follower 65, turning of the adjusting
screw 68 in or out will shift the follower toward one or the
other end of the spring chamber 56 and correspondingly vary
the normal spacing between the spacer 66 of the follower and
the confronting end of the shuttle 57. Once an adjustment
has been made, the adjusting screw 68 is held against backing
off and thus in selected position or setting by a set screw
71. To guard against accidental disturbance of or tampering
with an adjustment, both of the screws 68 and 71 preferably
are contained within the bore 51 after an adjustment and
fitted in their outer ends for turning by a special tool, such
as a socket wrench.
The resistance to compression of a coil spring, such
as the preferred spring 58, increases substantially in direct
proportion to the extent of compression or shortening of the
spring, after a relatively low-resistance initial compression
from free height. With the spring follower 65 adjustably -
positionable in the spring chamber 56 for both precompressing
the spring 58 and predetermining the extent of its compres-
sion between the open and closed positions of the shuttle 57
and the spring of suitable strength and free height, the pres-
sure regulator valve 5 is adapted to regulate within close
or narrow limits the pressure required in the filter unit 2
before the valve will pass filtered compressed air to the
reservoir. Back pressure in the spring chamber 56 is elimi-
nated as a factor in the pressure regulation by connecting
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1CD78347
that chamber to atmosphere through a bleed port 72 in the side
of the cap 50. -
Almost invariably, the hot dirty air from a compressor
is at least saturated with moisture and, unless incorporating
,
either a dehydrating or a refrigerating agent or means, a
compressed air filter, regardless of its efficiency in
removing excess moisture by condensation, even theoretically
cannot reduce the temperature of the air it discharges below
ambient or the air's moisture content below saturation at the
discharging pressure. Practically, filters not incorporat-
ing either of such agents, herein sometimes termed "filters of
the non-desiccant type" or "non-desiccant filters", have
heretofore been incapable of cooling air to a temperature
approaching ambient and have left the reservoir, when fully
charged, super-saturated with moisture, to the detriment of
devices operated by reservoir air. However, the outlet pres-
sure regulator valve 5, given a filter capable of discharging ;
air reduced in moisture content to saturation and approaching
ambient in temperature, can hold the moisture content of the
air in the reservoir to and even below saturation.
The absolute moisture content of saturated air increaseswith increase in temperature and decreases with increase in
pressure. Thus, absent a substantial intervening temperature
drop, a filter passing saturated compressed air to a reservoir
only when the air is at or above maximum reservoir pressure, will
cause the air in the compressor, when fully charged, to be at -~
most saturated and, if the passing pressure is above maximum
reservoir, to be unsaturated due to the expansion of the air
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1~78347
in the lesser pressure of the reservoir. In the truck, bus and
rapid transit car installations for which the illustrated filter
assembly 1 is particularly designed, the usual minimum and
maximum reservoir pressures are, respectively, about 104.7 p.s.i.a.
(7.31 kg.s.cm.a.) and 134.7 p.s.i.a. (9.47 kg.s.cm.a.).
Ad]ustable within narrow limits in the pressure at
which it will open, the pressure regulator valve 5 preferably is
preset or predetermined to pass filtered air from the filter
unit 2 at substantially maximum reservoir pressure, the term
"substantially", as here used, denoting a pressure in a preferred
range from maximum reservoir up to about 10 p.s.i. (0.70 kg.s.
cm.) thereabove. A sudden drop in ambient termperature when
the compressor is idling, could produce a super-saturated con-
dition in the air in the reservoir, but, unless the drop is ~-
drastic and protracted, this is unlikely, since the temperature
within the reservoir is slow to respond to change and interven-
ing pumping from the cooler air would negate it. As opposed,
a filter equipped with an outlet check valve in the conventional
manner, would begin to pass at least saturated air to the
reservoir at only slightly above reservoir minimum and continue
to pass air at progressively increasing pressure until reser-
voir maximum was finally reached, with the inevitable result
that the air in the reservoir, when fully charged, would be
super-saturated. ~
Although the pressure regulator valve 5 does increase -
the amount of moisture condensed in forcing the air in the
filter unit to reach and be at a predetermined maximum before it
can pass to the reservoir, other components of the assembly 1 and
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1~78347
particularly the filter unit 2, inlet valve 4 and preliminary
cooling unit 6 are otherwise responsible for and toyether capable
of delivering filtered air to the outlet port 20 at a tempera-
ture closely approaching ambient and with its moisture content
reduced to saturation at the outlet temperature and pressure.
The burden of cooling and filtering the hot dirty air received
from the compressor during the pumping cycle falls principally
upon the filter unit 2, in which air is centrifugally cooled
and heavier contaminants separated or filtered in the helical
passage 15, excess moisture is condensed in that passage and
the sump 17, with some further cooling in the bottom bowl 9
and annular passage 28, and oil and like droplets are filtered ;
or trapped in the scrubber 21. The preliminary cooling unit 6
furnishes additional centrifugal cooling and some separation
of contaminants, with its effect on the overall cooling enhanced
by the heat insulation of its body 43 from the housing 3.
The third component, the inlet valve 4, in automati-
cally closing at the start of the compressor's idling cycle,
preferably in response to governor line pressure, blocks ertry
into the cooling and filteringunits 6 and 2 of hot air from the
idling compressor at a pressure too low for effective centri-
fugal cooling. As a result, there is no heat build-up from that
source in the body 43 and housing 3, which the assembly 1 other- ~-
wise would have to dissipate in its next filtering cycle, with
consequent reductlon in its cooling efficiency over at least the
early part of that cycle. Additionally, when the assembly is
used with a compressor not having an aftercooler, the valve 4
will have the illustrated alternately opening exhaust port 37
and be able to dissipate the heat of the hot air by exhausting
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1C~7~3347
the air to atmosphere through the then open port, at the same
time, by enabling the air to flow therethrough, preventing
heat from building up in the valve itself and the supply line
leading to it from the compressor.
In operation, the filter assembly 1 is automatically
synchronized in its filtering and draining cycles with the
pumping and idling cycles, respectively, of the compressor, by the
automatic simultaneous change or shift to and from normal
condition in response, respectively, to the forces of their ~
own return springs and to governor line pressure, of the normal- `
ly open inlet valve 4 and normally closed drain valve 7. With
no pressure then in the governor line and the inlet valve 4 ~ '
thus open and the drain valve 7 closed, the assembly 1, through-
out the pumping cycle, receives hot dirty air from the com-
pressor, cools and filters the air in the cooling and filter
units 6 and 2 and passes cool filtered air in moisture-satur- ;;
ated condition to the reservoir, but only when the air in the
filter unit is at the predetermined, preferably substantially -~
maximum reservoir pressure at which the outlet pressure regula-
tor valve 5 has been preset to open.
The pumping cycle of the compressor and filtering
cycle of the filter assembly 1 continue until the reservoir
is fully charged with air at maximum reservoir pressure. On
sensing that cut-out condition, the governor shifts the com-
pressor from its pumping to its idling cycle, in process
diverting pressure to the governor line. At the start of
the idling cycle, there is simultaneous automatic closing of the
inlet valve 4 and opening of the drain valve 7, both in the
preferred embodiment in response to the governor line pressure. ~`
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~ai783~7 ~
Since the pressure regulator valve 5, acting as a check valve,
always blocks reverse flow from the reservoir to the filter
unit 2, the filter and coollng units 2 and 6 are then cut off
from both the compressor and the reservoir and open only to
atmosphere through the drain valve 7 and this condition obtains -
for the duration of the idling cycle.
In truck, bus and like installations, the compressor
will continue to idle until the demands of operating equipment
for compressed air have reduced the air pressure in the reser- ~
voir to reservoir minimum and, depending on road conditions, the ~ -
idling cycle may vary from as little as about 25 seconds to
over 2 hours, as opposed to an average pumping cycle of about
45 to 55 seconds. But however short the idling cycle, the
time required to discharge or drain contaminants from the filter
unit 2 is far shorter. The driving force is the compressed
air in the filter unit when the drain valve 7 opens that was ;
stored in the unit during the pumping cycle. With the large
volume of the chamber 29 available for such storage, the effect
of opening the drain valve 7 is ~o release to atmosphere an
air blast of such force as not only to drive out through the
exhaust port 33 contaminants collected in the sump 17 but also
by suction to purge the scrubber of any contaminants it trapped
during the filtering. The filter unit 2 will exhaust air until
its interior pressure is reduced to atmospheric and this is
the dura~ion of the draining cycle, a matter usually of a second
or less given ample openings in the exhaust port and the drain
valve.
From the above detailed description it will be apparent
that there has been provided an improved compressed air filter
asser~ly which is adapted to pass to a reservoir filtered air
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~L~78347 ~;
reduced in moisture content to saturation and in temperature
approximately to ambient, but only when the air is at substan-
tially maximum reservoir or other predetermined pressure. It
should be understood that the described and disclosed embodi-
ment is merely exemplary of the invention and that all
modifications are intended to be included that do not depart
from the spirit of the invention and the scope of the appended
claims.
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