Note: Descriptions are shown in the official language in which they were submitted.
CA 02950691 2016-11-29
WO 2015/195092 PCT/US2014/042672
TITLE
COMPRESSOR AFTERCOOLER BYPASS WITH INTEGRAL WATER SEPARATOR
BACKGROUND OF THE INVENTION
1. FIELD OF THE INVENTION
[0001] The present invention relates to compressor aftercooler bypass
systems and,
more particularly, to an aftercooler bypass having integral water separator.
2. DESCRIPTION OF THE RELATED ART
[0002] Railway braking systems rely on, among other things, air
compressors to
generate the compressed air of the pneumatic braking system. As the
compression of air
results in heating of the air to temperatures that are too hot for braking
systems, railway air
compressors are generally provided with an aftercooler to cool the compressed
air to 20 F to
40 F above ambient temperature. The cooled, compressed air is then supplied
to the air
supply system of a locomotive through a compressor discharge pipe that
connects to the first
main reservoir. This discharge pipe may be as long as 30 feet, and may
necessarily include
several ninety degree bends. In winter operation, when the ambient air
temperature can be
well below freezing (32 F), water vapor and water aerosol in the compressed
air stream can
freeze in the compressor discharge pipe, thereby at least partially blocking
the flow of air to
the braking system and adversely interfering with the operation of the braking
system.
[0003] As is well known to those skilled in the art, and described by a
body of
knowledge known as psychrometrics, the maximum total amount of water vapor in
a volume
of air is strongly dependent on the air temperature, as warm air is able to
hold much more
water vapor than cool air. This effect is characterized as the partial
pressure saturation
pressure. Further, as is also well known, the water vapor saturation partial
pressure is the
maximum water vapor in air at that temperature, regardless of air pressure. As
air is
compressed, the water vapor in the air will also be compressed, until the
water vapor partial
pressure equals the saturation pressure. The net result is that for a railway
compressor with a
10.5:1 compression ratio, intake air as dry as 9.5 percent relative humidity
will be at 100
percent relative humidity after compression. Lastly, due to the thermodynamics
of air, the
temperature of the air increases significantly as a result of compression. For
a two-stage
railway compressor, the second stage discharge temperature may be as high as
300 F above
ambient temperature.
[0004] Thus, based on the temperature dependent water vapor holding
capacity of air
and the effect of the compression on the water holding capacity of the air,
the hot air
discharged from the second stage of an air compressor may contain a
significant amount of
1
CA 02950691 2016-11-29
WO 2015/195092 PCT/US2014/042672
water vapor. As this hot air flows through a compressor aftercooler, the air
temperature is
reduced to 20 F to 40 F above ambient temperature. Air at this temperature
can hold much
less water vapor than air at the second stage discharge temperature, so the
excess water vapor
precipitates out as liquid water and/or water aerosol. When this liquid water
is transported
into the compressor discharge pipe, it may freeze if the discharge pipe and
ambient air are
cold enough. In addition, because the air exiting the compressor is 20 F to
40 F above
ambient air temperature, it is subject to further cooling in the compressor
discharge pipe. As
the air temperature drops in the pipe, further water will precipitate out
thereby compounding
the problem.
BRIEF SUMMARY OF THE INVENTION
[0005] The present invention comprises an air compressor for railway
braking system
that includes an integrated aftercooler bypass valve and integral water
separator to prevent
freezing of the compressor discharge pipe in winter operation. An integrated
aftercooler
bypass valve controllably connects the outlet of the second stage of the
compressor to the
outlet of the aftercooler. When the aftercooler bypass valve is open, then a
fraction of the hot
air from the compressor second stage outlet flows to the mixing chamber of the
aftercooler
bypass valve assembly, thereby bypassing the aftercooler. The remaining
fraction of the hot
air from the compressor second stage outlet flows through the aftercooler and
is cooled to a
temperature of 20 F to 40 F above ambient temperature as in conventional
aftercooling
systems. This cooled fraction of air from the aftercooler is directed to a
second inlet port on
the aftercooler bypass valve assembly to the mixing chamber, where it is mixed
with the hot
air from the first fraction of air. The combined air has a new temperature
which is a mass-
temperature average of the two air streams and the new outlet air temperature
is the result of
the relative mass flow of the two air streams, which is a consequence of the
flow capacity of
the open bypass valve. For example, the flow capacity of the open bypass valve
could be
selected to provide a new, mixed compressor outlet temperature of 140 F above
ambient
temperature so that even if the ambient air temperature was -40 F, the outlet
air temperature
presented to the discharge pipe would be 100 F. The outlet air temperature
can therefore be
selected to have a high-enough temperature so that even after flowing through
the cold
discharge pipe the air has sufficient heat that it remains above 32 F, thus
preventing freezing
in the pipe.
[0006] When the bypass valve is closed, all of the hot air from the
compressor second
stage outlet flows through the aftercooler and is cooled to a temperature of
20 F to 40 F
above ambient temperature. The aftercooler bypass valve is controlled to be
opened or
2
CA 02950691 2016-11-29
WO 2015/195092 PCT/US2014/042672
closed depending on optionally either ambient temperature and/or the
compressor system
outlet temperature. When the ambient temperature is below a threshold, such as
32 F, then
the aftercooler bypass valve is opened. At temperatures above the control
temperature, the
aftercooler bypass valve is closed.
[0007] The aftercooler bypass valve assembly optionally includes an
integral water
separator to remove the liquid and aerosol water from the outlet air stream.
By making the
water separator part of the aftercooler bypass valve assembly, the water
separator is
operational when the aftercooler bypass valve is open and when it is closed.
Furthermore,
packaging the water separator with the aftercooler bypass valve assembly
simplifies the
design, reduces the cost, eliminates piping connections and makes for a more
compact
arrangement.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)
[0008] The present invention will be more fully understood and
appreciated by
reading the following Detailed Description in conjunction with the
accompanying drawings,
in which:
[0009] Figure 1 is a perspective view of an aftercooler bypass system
according to the
present invention;
[0010] Figure 2 is a flow diagram of an aftercooler bypass system
according to the
present invention; and
[0011] Figure 3 is a cross-sectional view of an embodiment of a bypass
valve
according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0012] Referring now to the drawings, wherein like reference numerals
refer to like
parts throughout, there is seen in Fig. 1 an after cooler bypass system 10.
System 10 is
interconnected to an air compressor 12 via a connector duct 14 that is fluidly
interconnected
to the second stage outlet 16 of compressor 12 so that at least a portion of
the air exiting
compressor 12 may be redirected to system 10 away from the aftercooler inlet
pipe 18 of a
conventional aftercooler 20. Connector duct 14 diverts the compressed air
exiting outlet 16
of air compressor 12 to a bypass valve assembly 22 having a mixing chamber 24.
Mixing
chamber 24 is also is interconnected to the discharge flange 34 of aftercooler
20, so that
cooled air exiting aftercooler 20 may be intermixed with the hot air diverted
by connector
duct 14. Valve assembly 22 further comprises a bypass valve 26 that may be
selectively
opened or closed, or at least partially opened, based on a threshold, such as
the ambient air
temperature. Valve assembly 22 preferably comprises a water separator 28
attached thereto
3
CA 02950691 2016-11-29
WO 2015/195092 PCT/US2014/042672
and positioned proximately to mixing chamber 24 to assist with the removal of
water from
the intermixed air streams. The intermixed air in mixing chamber 24 may then
be provided
to the braking system via an outlet flange 42 that can connect to the
conventional discharge
piping used to conduct compressed air to the main reservoir of the braking
system. When
bypass valve 26 is closed, the cooled compressed air exiting aftercooler 20
will still pass
through mixing chamber 24 so that water separator 28 can remove any undesired
water and
then exit to the braking system via flange 42.
[0013] Bypass valve 26 is preferably dimensioned to provide a
predetermined mixing
ratio of bypassed air and thus result in a predetermined outlet temperature
above ambient
temperature when ambient air temperatures fall below as threshold, such as
freezing.
Alternatively, as explained below, valve 26 may be controlled to adaptively
maintain mixed
air temperature based on the ambient air temperature. Furthermore, as seen in
Fig. 1,
aftercooler bypass valve assembly 22 may be formed as a single, integral unit
that may be
installed or replaced as a single unit for easer installation or repair in the
field.
[0014] Referring to Fig. 2, bypass valve 26 selectively allows compressed
air leaving
compressor 12 to bypass aftercooler 20 and then intermix with the cooled air
leaving
aftercooler 20 by discharge flange 34. Thus, bypass valve assembly 22 provides
a direct and
short bypass of aftercooler 20 so that when bypass valve 26 is open, the flow
resistance
through bypass valve assembly 22 is less than the flow resistance through
aftercooler 20. As
a result, a substantive fraction of hot air will preferentially flow through
bypass valve 26 into
mixing chamber 24. This arrangement is significantly simpler and less costly
than
conventional approaches that necessitate the use of a three-way valve to
simultaneously block
the connection to an aftercooler while opening another connection to an
aftercooler bypass
line.
[0015] As seen in Fig. 1, water separator 28 preferably includes an
automatic drain
valve 30 to expel liquid and aerosol water from the outlet air stream. While
drain valve 30 is
shown schematically in Fig. 2 as a solenoid valve on the bottom of the
reservoir 32 of water
separator 28, drain valve 30 could additionally comprise a pneumatically
piloted drain valve
at the bottom of the reservoir, with the controlling solenoid integrated into
the block of
aftercooler bypass valve 22. Reservoir 32 of water separator 28 may include an
integral,
pneumatic connection between the solenoid valve 30 in the valve block and the
pneumatically piloted drain valve in the bottom of the reservoir, so that the
water separator
reservoir could be removed for maintenance without disturbing electrical
wiring or piping.
4
CA 02950691 2016-11-29
WO 2015/195092 PCT/US2014/042672
[0016] While bypass valve 26 could be formed using a suitable two-way
valve known
in the art, bypass valve 26 may also be made in the same manner as the
unloading valves 64
of the cylinder heads of air compressor 12, as these valves are designed to
operate reliably at
the high temperature and pressure of the second stage cylinder outlet. For
example, as seen
in Fig. 3, bypass valve 26 may comprise a housing 50 having a control input 52
for
controlling the position of a valve 54 positioned within housing 50 and biased
by one or more
springs 56 for movement between a closed position, where valve 52 engaged a
seat 58
formed in housing 50, and an open position, where valve 52 allow an inlet port
60 to be in
communication with an outlet port 62. Preferably valve 54 and seat 58 form a
metal to metal
contact for reliable operation at the high temperatures and pressures
associated with system
10. Inlet port 60 is interconnected to second stage outlet 16 of compressor 12
by connector
duct 14, and outlet port 62 is interconnected to mixing chamber 24. Using the
same
manufacturing process for both bypass valve 26 and the unloading valves 64 of
air
compressor 12 reduces the variety of parts necessary for initial manufacture
and for periodic
remanufacture and maintenance.
[0017] While the forgoing description is discussed in the context of a
two-state
aftercooler bypass valve 26, i.e., either open or closed, bypass valve 26
could optionally be a
proportional valve that would allow the outlet temperature of aftercooler 20
to be controlled
over a range of temperatures. For example, the outlet temperature could be
controlled by an
associated controller 36 having an ambient air thermometer 38, or comparable
sensor, as well
as an inline temperature sensor 40 downstream of mixing chamber 24. Thus, the
outlet
temperature could be set to 100 F whenever the ambient temperature is at or
below freezing
by varying the opening of aftercooler bypass valve 26 to provide the needed
high temperature
air flow to mixing chamber 24. For example, if the ambient temperature was
above 32 F,
then the aftercooler bypass controller 36 would close aftercooler bypass valve
26 and all the
air volume would flow through the aftercooler so that the compressor outlet
temperature is
20 F to 40 F above ambient temperature. Similarly, when temperatures were
below 32 F,
then the aftercooler bypass controller 36 would open bypass valve 26 enough to
maintain an
outlet temperature of about 100 F or whatever temperature is desired. Thus,
bypass valve 26
and controller 36 may be configured to provide closed-loop control of the
outlet temperature,
thereby providing a variable mixing ratio and a controllable outlet
temperature independent
of ambient temperature.
