Abstrict An air dryer for compressed air braking systems includes a desiccant
canister which is provided with a double helix insert which cooperates
with the walls of the canister to define a pair of intertwined,
serpentine, pneumatically isolated flow paths. The flow paths extend
through the canister between the end walls and are filled with a
desiccant material. A single center line valve mechanism is provided
to switch between the flow paths so that one of the flow paths is
purged at the same time that the other flow path is pressurized.
Claims We claim:
1. Air dryer for a compressed air system comprising a housing,
a desiccant canister carried by the housing, said canister being
defined by a circumferentially extending wall and a pair of opposite
end walls, a double helix insert within said canister and cooperating
with said walls to define a pair of intertwined, serpentine, pneumatically
isolated flow paths through said canister and extending between
said end walls, each of said flow paths being filled with desiccant,
and valve means carried by said housing for controlling communication
through said flow paths.
2. Air dryer as claimed in claim 1 wherein both of said flow paths
communicate with a common delivery chamber, and a pair of check
valves, each of said check valves controlling communication between
a corresponding one of said flow paths and said delivery chamber.
3. Air dryer as claimed in claim 1 wherein said housing includes
a supply port for supplying compressed air to said canister, said
valve means including a shuttle valve for switching communication
from said supply port to one of said flow paths and then to the
other flow path.
4. Air dryer as claimed in claim 2 wherein said housing includes
a supply port for supplying compressed air to said canister and
purge port means for communicating said flow paths to atmosphere,
said valve means including a shuttle valve for communicating said
supply port to one of said flow paths while communicating the other
flow path to said purge port means and then switching to communicate
the other flow path to the supply port and the one flow path to
the purge port means.
5. Air dryer as claimed in claim 4 wherein a flow restricting
purge orifice communicates each of said flow paths with said common
delivery chamber.
6. Air dryer as claimed in claim 2 wherein a flow restricting
purge orifice communicates each of said flow paths with said common
delivery chamber.
7. Air dryer as claimed in claim 4 wherein said housing includes
an unloader port, said shuttle valve means including means responsive
to the pressure level at the unloader port to shift the shuttle
valve means to a position communicating both of said flow paths
to said purge port means.
8. Air dryer for a compressed air system comprising a housing,
a desiccant canister carried by the housing, said canister being
defined by a circumferentially extending wall defining a chamber
therewithin and a pair of opposite end walls closing opposite ends
of the chamber, dividing means for dividing said chamber into a
pair of pneumatically isolated flow paths, each of said flow paths
extending between each of the opposite end walls, each of said flow
paths being filled with desiccant, and valve means carried by said
housing for controlling communication through said flow paths, both
of said flow paths communicating with a common delivery chamber,
and a pair of check valves, each of said check valves controlling
communication between a corresponding one of said flow paths and
said delivery chamber.
9. Air dryer as claimed in claim 8 wherein said dividing means
divides said chamber into a pair of serpentine flow paths.
10. Air dryer as claimed in claim 9 wherein said flow paths are
intertwined.
11. Air dryer as claimed in claim 8 wherein said housing includes
a supply port for supplying compressed air to said canister, said
valve means including a shuttle valve for switching communication
from said supply port to one of said flow paths and then to the
other flow path.
12. Air dryer as claimed in claim 8 wherein said housing includes
a supply port for supplying compressed air to said canister and
purge port means for communicating said flow paths to atmosphere,
said valve means including a shuttle valve for communicating said
supply port to one of said flow paths while communicating the other
flow path to said purge port means and then switching to communicate
the other flow path to the supply port and the one flow path to
the purge port means.
13. Air dryer as claimed in claim 12 wherein a flow restricting
purge orifice communicates each of said flow paths with said common
delivery chamber.
14. Air dryer as claimed in claim 8 wherein a flow restricting
purge orifice communicates each of said flow paths with said common
delivery chamber.
15. Air dryer as claimed in claim 12 wherein said housing includes
an unloader port, said shuttle valve means including means responsive
to the pressure level at the unloader port to shift the shuttle
valve means to a position communicating both of said flow paths
to said purge port means.
16. Air dryer for a compressed air system comprising a housing,
a desiccant canister carried by the housing, said canister being
defined by a circumferentially extending wall defining a chamber
therewithin and a pair of opposite end walls closing opposite ends
of the chamber, dividing means for dividing said chamber into a
pair of pneumatically isolated flow paths, each of said flow paths
extending between each of the opposite end walls, each of said flow
paths being filled with desiccant, and valve means carried by said
housing for controlling communication through said flow paths, said
housing including a supply port for supplying compressed air to
said canister and purge port means for communicating said flow paths
to atmosphere, said valve means including a shuttle valve for communicating
said supply port to one of said flow paths while communicating the
other flow path to said purge port means and then switching to communicate
the other flow path to the supply port and the one flow path to
the purge port means.
17. Air dryer as claimed in claim 16 wherein said dividing means
divides said chamber into a pair of serpentine flow paths.
18. Air dryer as claimed in claim 16 wherein said flow paths are
intertwined.
Description This invention relates to an air dryer for a compressed air braking
system.
Air dryers have been used for many years to remove moisture from
the compressed air used in compressed air braking systems used on
heavy vehicles. These air dryers are of two basic types. The continuous
flow type usually includes two separate desiccant beds and a timing
mechanism to switch flow between the beds. When one of the beds
is drying air, the other desiccant bed is being purged and regenerated.
Continuous flow systems are normally used in application with heavy
air consumption, such as transit buses. On applications with lower
air consumption requirements, such as line haul trucks, a single
bed desiccant cartridge is used. A single bed requires a dedicated
purge volume, which may be incorporated into the air dryer unit
itself, or mounted remotely. The present invention provides a twin-bed
continuous flow air dryer of the same or smaller size of prior art
single bed air dryers. The drying capacity of a desiccant bed is
a function of the length to diameter (L/D) ratio of the bed, a higher
L/D ratio being more efficient than a lower L/D ratio desiccant
bed. Accordingly, the present invention provides a double helix
insert in the desiccant canister, thereby dividing the canister
into pneumatically isolated, serpentine, intertwined desiccant beds.
Each of the desiccant beds has a relatively high length to diameter
ratio as compared to prior art air dryers.
This and other advantages of the present invention will become
apparent from the following description, with reference to the accompanying
drawings, in which:
FIG. 1 is a cross-sectional view of a continuous flow air dryer
made pursuant to the teachings of the present invention;
FIG. 2 is a view similar to FIG. 1 but showing the shuttle valve
which controls flow between the beds in a position different from
the position of the shuttle valve in FIG. 1; and
FIG. 3 is a view similar to FIGS. 1 and 2 but illustrating the
shuttle valve in a third position different from the positions in
which the shuttle valve is illustrated in FIGS. 1 and 2.
Referring now to the drawings, an air dryer generally indicated
by the numeral 10 includes a desiccant canister 12 mounted on a
housing 14 containing a shuttle valve generally indicated by the
numeral 16. The housing 14 includes a supply port 18 which is communicated
to a source of compressed air, such as the vehicle air compressor;
a pair of purge ports 20 and 26 which are communicated to ambient
atmosphere; an unloading port 22 which receives a pressure signal
communicated by the vehicle compressor unloader; and a control port
24 which is communicated to a timed control signal, that is, a
signal controlled by a timed solenoid valve which communicates a
pressure signal to the control port 24 for a predetermined time
period and then exhausts the signal from port 24 to atmosphere for
an equivalent time period.
The desiccant canister 12 includes a circumferentially extending
wall 28 bounded by upper and lower end walls 30 32. End wall 32
is provided with circumferentially extending seals 34 which sealing
engage the housing 14 and is also provided with a threaded connection
36 which engages threaded stud 38 when the canister 12 is installed
on the housing 14. A cover member 40 cooperates with the end wall
30 to define a delivery chamber 42 therewithin. A delivery check
valve 44 permits communication from the delivery chamber 42 to a
delivery port 46 but prevents communication in the reverse direction.
Delivery port 46 is communicated to appropriate storage reservoirs
(not shown).
A double helix insert generally indicated by the numeral 48 is
installed within the canister 12. The insert 48 includes a central
stem 50 and a radially extending, axially inclined, continuous fin
52 projecting from the stem 50. The outer periphery of the fin 52
engages the circumferentially extending wall 28 of the desiccant
canister 12. Opposite sides of the fin 52 cooperate to define a
first flow path 54 and a second flow path 56. Because the flow paths
54 56 are defined by opposite sides of the fin 52 the flow paths
54 56 are intertwined in that the flow path 54 wraps around the
flow path 56 and the flow path 56 wraps around the flow path 54
as illustrated in the drawings. Because both of the flow paths 54
56 revolve around the central stem 50 each of the flow paths 54
and 56 define a serpentine path extending between the bottom and
top of the desiccant canister 12. Both of the flow paths 54 and
56 are filled with desiccant beads, a few of which are indicated
as at 58. The fin 52 maintains pneumatic isolation between the flow
paths 54 and 56.
The upper end plate 30 is loaded downwardly by a spring 60 in the
delivery chamber 42 to maintain pressures on the desiccant beads
58. A one-way check valve 62 permits communication from the flow
path 56 into the delivery chamber 42 but prevents communication
in reverse direction. Similarly, another one-way check valve 64
permits communication between the flow path 54 in the delivery chamber
42 but prevents communication in the reverse direction. A flow
restricting orifice 66 permits communication, at a limited rate,
from the delivery chamber 42 into the flow path 56 when the pressure
in the flow path 56 drops below that in the delivery chamber 42
and another flow restricting orifice 68 similarly permits limited
communication from the delivery chamber 42 into the flow path 54
when the pressure in flow path 54 drops below that in delivery chamber
42.
The housing 14 includes a passage 70 which communicates with the
flow path 54 and another passage 72 which communicates with the
flow path 56. The shuttle valve 16 controls communication between
the supply port 18 and the passages 70 and 72 between the passage
70 and the purge port 26 and between the passage 72 and the purge
port 20. Accordingly, shuttle valve 16 includes a stem 74 having
enlarged valve elements 76 78 mounted on opposite ends thereof.
Valve element 76 cooperates with a valve seat 80 circumscribing
purge port 26 to control communication through purge port 26 and
the valve element 78 cooperates with valve seat 82 to control communication
through the purge port 20. An inlet valve member 84 is mounted on
a sleeve 86 which is slidably mounted on the stem 74. Valve member
84 cooperates with circumferentially extending valve seat 88 to
control communication between inlet or supply port 18 and the passage
70. Similarly, another inlet valve member 90 is integral with a
sleeve 92 which is also slidably mounted on the stem 74. Valve member
90 cooperates with valve seat 93 to control communication between
the supply inlet port 18 and the passage 72. A spring 94 yieldably
urges the valve members 84 90 apart, so that the ends of the sleeves
86 92 are yieldably urged towards the corresponding valve member
76 or 78.
A piston 96 includes an extension 98 that is secured to the valve
member 78 so that the piston 96 is able to position the shuttle
valve 16 within the housing 14. A spring 100 yieldably urges the
piston 96 and therefore the shuttle valve 16 to the right, viewing
the Figures. The piston 96 is controlled by the pressure signals
communicated through control port 24. An unloader piston 102 is
responsive to the pressure level at unloader port 22 and includes
an extension 104 which engages the piston 96 when the unloader port
22 is pressurized and the pressure at control port 24 is vented,
as illustrated in FIG. 3.
In operation, the position of the shuttle valve as illustrated
in FIG. 1 is the position it assumes when the compressor is on load
(and thus the unloader port 22 is vented) and the control port 24
is pressurized. Accordingly, piston 96 is urged to the left, viewing
FIG. 1 thereby causing valve member 78 to close off communication
between the purge port 20 and passage 72 and causing the valve member
76 to open purge port 26 to thereby vent passage 70 and flow path
54 to atmosphere. At the same time, valve element 90 is moved away
from valve seat 93 permitting communication between the supply
port 18 and the passage 72 and therefore to the flow path 56. Accordingly,
compressed air communicates through the flow path 56 and out of
the check valve 62 into the delivery chamber 42. Flow is communicated
out of deliver chamber 42 and into the aforementioned reservoir
(not shown) through the check valve 44. At the same time, the flow
path 54 is communicated to atmosphere and thus is depressurized.
Accordingly, since the pressure level and flow path 54 is now less
than the pressure in delivery chamber 42 limited communication
through the flow restricting orifice 68 purges the desiccant in
the flow path 54.
As discussed above, after a predetermined time period, control
port 24 is vented. Accordingly, spring 100 acting against piston
96 moves the piston 96 and therefore the shuttle valve 16 to the
right, viewing the Figures, into the position illustrated in FIG.
2. In this position, the purge port 26 is closed and communication
is established between supply port 18 and passage 70 and therefor
into the flow path 54 thereby pressurizing flow path 54 to deliver
compressed air into the deliver chamber 42. At the same time, valve
member 90 is engaged with valve seat 36 thereby cutting off communication
between supply or inlet port 18 and the passage 72. The valve member
78 is also moved over away from the valve seat 82 thereby communicating
passage 72 and therefore the flow path 56 to atmosphere through
the purge port 20. Accordingly, flow path 56 is depressurized, permitting
limited communication through the flow restricting orifice 66 between
the delivery chamber 42 and the desiccant within the flow path 56
to thereby purge the desiccant 58 therein, in a matter well known
to those skilled in the art. It will be understood that, after the
aforementioned predetermined time period (assuming the compressor
remains on load) the pressure at the control port 24 will again
be switched, thereby moving the shuttle valve 16 back into the FIG.
1 position. Accordingly, the shuttle valve 16 is moved between the
position illustrated in FIGS. 1 and 2 on a periodic timed basis
as long as the compressor remains on load.
FIG. 3 illustrates the position of the components when the compressor
goes off load. In this condition, no pressure is available to the
supply inlet port 18 and the control port 24 is automatically vented,
permitting the spring 100 to urge the piston 96 to the right, viewing
the Figures. However, at this time, a pressure signal is communicated
by the unloader mechanism through the unloader port 22 simultaneously
with unloading of the compressor, thereby moving the unloader piston
102 to the left, viewing the Figures. Accordingly, as illustrated
in FIG. 3 the shuttle valve 16 is positioned in an intermediate
position between the FIG. 1 and FIG. 2 positions. In this case,
communication between the inlet or supply port 18 and both of the
passages 70 72 is cut off due to the engagement of the valve members
84 90 with their corresponding valve seats 88 93. At the same
time, the passage 70 is communicated to purge port 26 and the passage
72 is communicated to purge port 20 thereby simultaneously depressurizing
both of the flow paths 54 56. Accordingly, both of the fluid paths
54 and 56 are simultaneously purged by fluid pressure in the delivery
chamber 42 communicating through flow restricting orifice 66 68
until the pressure in the delivery chamber 42 reaches atmospheric
pressure . |