Note: Descriptions are shown in the official language in which they were submitted.
QUICK SERVICE LIMITING VALVE
BACKGROUND OF THE INVENTION
Field of the Invention
[0001] The present invention generally relates to brake apparatus for railway
vehicles and,
more particularly, to a valve for maintaining brake cylinder pressure for all
service brake
applications.
Description of Related Art
[0002] Railroad freight cars have a brake pipe that runs through each car and
is coupled
therebetween so as to extend continuously the length of the train. The brake
pipe is charged with
compressed air typically at the head end by a compressor on the locomotive.
The compressed air
not only provides the pneumatic brake force at the respective cars, but also
serves as a
communication link via which the car's brakes are controlled from the
locomotive by increasing
and decreasing the brake pipe pressure. Brake equipment for railroad freight
cars utilizes control
valves to control the operation of the brake cylinders and brakes for the
freight cars, such as the
ABDX control valve sold and manufactured by Wabtec Corporation.
[0003] When a train brake pipe is fully charged to the pressure setting of the
locomotive brake
valve device, a natural pressure gradient typically exists in the brake pipe
due to leakage caused
by wear and other issues resulting in pressure changes with the brake
cylinders. Assuming the
locomotive brake valve is set to charge the brake pipe to 90 psi, the pressure
at each car from the
front to the rear of the train will experience a slightly lower pressure due
to leakage and fluid
flow resistance as the pressure maintaining brake valve attempts to maintain
the leakage. The
brake pipe pressure will gradually rise from front to back in seeking the
natural pressure gradient
consistent with the application of brake pipe pressure at the locomotive.
[0004] Current brake systems for railway vehicles may also experience leakage
of pressurized
fluid into or out of the brake cylinder of the brake system. The Association
of American
Railroads' specification for a single railway car specifies allowable leakage
into/out of the brake
cylinder at the rate of +/- 1 psi/min. At this rate, acceptable loss of brake
cylinder pressure is
permitted while still safely maintaining brake cylinder pressure levels for
the operation of the
railway vehicle's brake system. When operating a railway vehicle on a grade
for an extended
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period of time, however, a minimal level of leakage out of the brake cylinder
in one minute can
decrease to a low enough pressure to result in reduced braking effort.
SUMMARY OF THE INVENTION
[0005] In one aspect, a quick service limiting valve includes a housing
defining an interior
chamber, a brake pipe passageway, and a brake cylinder passageway, a valve
member received
within the interior chamber of the housing, with the valve member including a
body, a first seal,
a second seal, and a valve spring. The body of the valve member defines a
valve passageway,
with the valve member having a first position where the valve passageway
allows fluid
communication between the brake pipe passageway and the brake cylinder
passageway and a
second position where the brake pipe passageway is isolated from the brake
cylinder
passageway. The valve spring biases the valve member to the second position.
The quick
service limiting valve also includes a follower assembly received within the
interior chamber of
the housing, with the follower assembly including a body, a first check valve,
a second check
valve, a diaphragm, and a follower spring, with the diaphragm having a first
side in fluid
communication with the brake cylinder passageway and a second side in fluid
communication
with a reference chamber. The first check valve has a first position where the
brake cylinder
passage is in fluid communication with the reference chamber and a second
position where the
brake cylinder passage is isolated from the reference chamber. The second
check valve has a
first position where the reference chamber is in fluid communication with the
brake cylinder
passageway and a second position where the reference chamber is isolated from
the brake
cylinder passageway. The follower spring biases the valve member toward the
first position.
The valve member is configured to move between the first position and the
second position
based on a pressure differential between a pressure of the brake cylinder
passage and a pressure
of the reference chamber.
[0006] The first check valve may be a one-way check valve only allowing air
flow into the
reference chamber. The first check valve may include a check body and a check
spring, the
check spring biasing the first check valve to the second position into
engagement with a seat
defined by the body of the follower.
[0007] The second check valve may be a one-way check valve only allowing air
flow from the
reference volume to the brake cylinder passageway. The second check valve may
be an umbrella
valve.
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[0008] The valve member may further include a backflow check valve configured
to prevent
flow from the brake cylinder passageway to the brake pipe passageway. The
backflow check
valve may be received within the valve passageway of the valve member, with
the back flow
check valve including a spring seat, backflow spring, and a valve member. The
valve member of
the backflow check valve may be spherical.
[0009] The follower assembly may include a choke positioned between the brake
cylinder
passageway and the first check valve. The choke may include a filter.
[0010] The housing and the second side of the diaphragm may define the
reference chamber.
[0011] The first and second seals of the valve member may form a seal between
the housing
and the first and second seals. The first and second seals may be 0-rings. The
first and second
seals may be secured to the valve member. The valve passageway of the valve
member may
include a central opening extending along a longitudinal axis of the body of
the valve member
and a first through hole extending in a radial direction relative to the
longitudinal axis of the
body of the valve member. The valve passageway of the valve member may further
include a
second through hole extending in a radial direction relative to the
longitudinal axis of the body of
the valve member, with the second through hole axially spaced from the first
through hole. The
first through hole of the valve passageway of the valve member may be
positioned between the
first and second seals. An opening of the brake pipe passageway may be
positioned between the
first and second seals when the valve member is in the first position. The
first and second
through holes of the valve passageway may be configured to form a choke to
restrict flow from
the brake pipe passageway to the brake cylinder passageway when the valve
member is in the
first position.
[0012] The body of the follower assembly may be secured to the diaphragm, and
the body of
the follower assembly may engage the valve member.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a cross-sectional view of a quick service limiting valve
according to one
aspect of the present invention, showing a first position of the valve.
[0014] FIG. 2 is a cross-sectional view of the valve of FIG. 1, showing a
second position of
the valve.
[0015] FIG. 3 is a top view of a follower assembly according to one aspect of
the present
invention.
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[0016] FIG. 4 is a cross-sectional view along line A-A shown in FIG. 3.
[0017] FIG. 5 is an exploded perspective view of the follower assembly of FIG.
3.
[0018] FIG. 6 is a front view of a stem valve assembly according to one aspect
of the present
invention.
[0019] FIG. 7 is a cross-sectional view along line A-A shown in FIG. 6.
[0020] FIG. 8 is an exploded perspective view of the stem valve assembly of
FIG. 6.
DETAILED DESCRIPTION
[0021] For purposes of the description hereinafter, spatial orientation terms,
if used, shall
relate to the referenced embodiment as it is oriented in the accompanying
drawing figures or
otherwise described in the following detailed description. However, it is to
be understood that
the embodiments described hereinafter may assume many alternative variations
and
embodiments. It is also to be understood that the specific devices illustrated
in the
accompanying drawing figures and described herein are simply exemplary and
should not be
considered as limiting.
[0022] There are two types of demand on brake pipe pressure: continuous and
temporary.
Continuous leakage exists in the train line regardless of release or applied
status of the brake
cylinder. Temporary demand occurs on the brake pipe during a brake application
with control
valves applying temporary demand on the brake pipe to augment the service
brake application
signal transmission. Continuous demand on brake pipe creates a continuous flow
into the train
brake system to maintain brake pipe pressure. Continuous demand results in a
pressure gradient
from the front to the rear of a train. Temporary demand on brake pipe allows
the manipulation
of brake pipe at each car to develop cylinder pressure in a timely fashion.
Typical freight control
valves incorporate three distinct manipulations of brake pipe pressure, which
are temporary.
Temporary demands on brake pipe include: Preliminary Quick Service; Quick
Service Limiting
Valve (QSLV); and Accelerated Application Valve (AAV).
[0023] Preliminary Quick Service directs brake pipe pressure to a volume
(quick service bulb)
and is vented to atmosphere at the beginning of a brake application. This
connection provides a
local drop of brake pipe at each car to enhance the transmission of the brake
pipe pressure
reduction through the train. The Preliminary Quick Service isolates the brake
pipe connection
when the service piston moves into the service application position thereby
directing auxiliary
reservoir to brake cylinder. This demand on brake pipe is temporary.
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[0024] A conventional QSLV directs brake pipe pressure to brake cylinder when
a brake
application is made. When a brake application is made, the main piston directs
auxiliary
reservoir to brake cylinder and the QSLV directs brake pipe to brake cylinder.
When brake
cylinder reaches approximately 10 psi, the QSLV isolates brake pipe from brake
cylinder. This
demand on brake pipe is temporary. The QSLV, by FRA and AAR regulations, must
produce 8
to 12-psi brake cylinder pressure for a 5-psi brake pipe reduction. During a
brake application, a
conventional QSLV will reopen the connection between the brake pipe and brake
cylinder in the
event there is a loss of brake cylinder pressure that causes brake cylinder
pressure to fall below
psi. A conventional QSLV, however, will not maintain brake cylinder pressure
based on the
targeted cylinder pressure. For example, during a 20 psi brake cylinder
application, a
conventional QSLV will not maintain brake cylinder within certain range, such
as +/- 2 psi, of
the initial 20 psi target pressure.
[0025] Referring to FIGS. 1-8, according to one aspect of the present
invention, a quick
service limiting valve 10 is provided that maintains a target pressure within
a brake cylinder
during a brake application. The quick service limiting valve 10 includes a
housing 12 defining
an interior chamber 14, a brake pipe passageway 16, and a brake cylinder
passageway 18, a
valve member 20 received within the interior chamber 14 of the housing 12, and
a follower
assembly 22 received within the interior chamber 14 of the housing 12. The
brake pipe
passageway 16 is configured to be in fluid communication with a brake pipe
(not shown). The
brake cylinder passageway 18 is configured to be in fluid communication with a
brake cylinder
(not shown). The quick service limiting valve 10 may be provided integrally
with a control
valve, such as an ABDX control valve from Wabtec Corporation, although the
quick service
limiting valve 10 may also be provided as a separate component.
[0026] Referring to FIGS. 1, 2, and 6-8, the valve member 20 includes a body
30, a first seal
32, a second seal 34, and a valve spring 36. The body 30 of the valve member
20 has a first end
38 and a second end 40 and defines a valve passageway 42. The valve passageway
42 has a first
through hole 44 and a second through hole 46 in fluid communication with a
central opening 48.
The first and second through holes 44, 46 may be formed perpendicular to the
central opening
48. The first and second through holes 44, 46 are positioned intermediate the
first and second
ends 38, 40 of the body 30 of the valve member 20. The first seal 32 and the
second seal 34 may
be 0-rings, although other suitable seals may be utilized. The valve spring 36
may be a
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compression spring, although other suitable springs or biasing arrangements
may be utilized.
The valve member 20 has a first position (FIG. 1) where the valve passageway
42 allows fluid
communication between the brake pipe passageway 16 and the brake cylinder
passageway 18
and a second position (FIG. 2) where the brake pipe passageway 16 is isolated
from the brake
cylinder passageway 18. The valve spring 36 biases the valve member 20 to the
second position.
The valve member 20 also includes a backflow check valve 50 configured to
prevent flow from
the brake cylinder passageway 18 to the brake pipe 16. The backflow check
valve 50 is received
within the valve passageway 42 of the valve member 20 and includes a spring
seat 52, a
backflow spring 54, and a valve member 56. The backflow check valve 50 is a
ball check valve,
although other suitable valve arrangements may be utilized.
[0027] Referring to FIGS. 1-5, the follower assembly 22 includes a body 60, a
first check
valve 62, a second check valve 64, a diaphragm 66, and a follower spring 68.
The follower
spring 68 may be a compression spring, although other suitable springs or
biasing arrangements
may be utilized. The diaphragm 66 has a first side 70 in fluid communication
with the brake
cylinder passageway 18 and a second side 72 in fluid communication with a
reference chamber
74. The reference chamber 74 is defined within the interior chamber 14 of the
housing 12 by the
diaphragm 66 and the housing 12. The first check valve 62 has a first position
where the brake
cylinder passageway 18 is in fluid communication with the reference chamber 74
and a second
position where the brake cylinder passageway 18 is isolated from the reference
chamber 74. The
second check valve 64 has a first position where the reference chamber 74 is
in fluid
communication with the brake cylinder passageway 18 and a second position
where the
reference chamber 74 is isolated from the brake cylinder passageway 18. The
follower spring 68
biases the valve member 20 toward the first position. As discussed in more
detail below, the
valve member 20 is configured to move between the first position (FIG. 1) and
the second
position (FIG. 2) based on a pressure differential between a pressure of the
brake cylinder
passageway 18 and a pressure of the reference chamber 74 combined with the
follower spring
68.
[0028] Referring again to FIGS. 1-5, the first check valve 62 is a one-way
check valve that
only allows air flow into the reference chamber 74. The first check valve 62
includes a check
body 76 and a check spring 78. The check spring 78 biases the first check
valve 62 to the second
position into engagement with a seat 80 defined by the body 30 of the follower
assembly 22.
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The check spring 78 may be secured within the body 30 of the follower assembly
22 by a
retaining ring 82. The second check valve 64 is a one-way check valve that
only allows air flow
from the reference chamber 74 to the brake cylinder passageway 18. The second
check valve 64
is an umbrella valve, although other suitable valve arrangements may be
utilized. The follower
assembly 22 also includes a choke 84 positioned between the brake cylinder
passageway 18 and
the first check valve 62. The choke 84 is received by the body 30 of the
follower assembly 22.
Further, the choke 84 includes a filter 86 configured to prevent any debris
from preventing flow
through the choke 84. As discussed in more detail below, the choke 84 is
configured to restrict
the flow of air to the reference chamber 74 to prevent an erroneously high
target pressure from
being directed to the reference chamber 74. When the second check valve 64 is
in the first
position, air may flow from the reference chamber 74, through an exhaust
opening 88 defined by
the body 30 of the follower assembly 22, through the second check valve 64,
through an exhaust
passageway 90 in the body 30 of the follower assembly 22, through the choke
84, and into the
brake cylinder passageway 18.
[0029] Referring to FIGS. 1 and 2, during a brake application, brake cylinder
pressure enters
the interior chamber 14 of the housing 12 via the brake cylinder passageway
18, flows through
the filter 86 and the choke 84 and moves the first check valve 62 from the
second position to the
first position by unseating the check body 76 from the seat 80. With the first
check valve 62 in
the first position, brake cylinder pressure fills the reference chamber 74 to
provide a target
cylinder pressure that is used as a reference to determine when the drop in
the actual cylinder
pressure should be maintained by directing brake pipe to the brake cylinder.
Thus, according to
one aspect of the present invention, the target cylinder pressure is
determined by using the
maximum pressure that is developed for a given brake pipe reduction regardless
of piston travel
of the brake cylinder. The maximum cylinder pressure developed is used as the
reference
pressure to determine when brake pipe should be directed to cylinder. As noted
above, the choke
84 prevents an erroneously high target pressure from being directed to the
reference chamber 74
during initial brake cylinder pressure development. Further, the first check
valve 62 will not
move to the first position until the spring force of the check spring 78 is
overcome. The first
check valve 62 may open when the brake cylinder pressure increases above a
predetermined
value, such as 12 psi. The pressure in the reference chamber 74 will increase
until the force
generated from the check spring 78 and the pressure in the reference chamber
74 moves the first
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check valve 62 into the second position to isolate the brake cylinder
passageway 18 from the
reference chamber 74. Accordingly, brake cylinder pressure via the brake
cylinder passageway
18 will act on the first side 70 of the diaphragm 66 and pressure within the
reference chamber 74
corresponding to a target cylinder pressure will act on the second side 72 of
the diaphragm 66.
[0030] Referring again to FIGS. 1-2, when leakage out of the brake cylinder
exists, the
pressure of the reference chamber 74 remains constant on the second side 72 of
the diaphragm 66
while the brake cylinder pressure via the brake cylinder passageway 18 is
reduced. The pressure
differential causes the valve member 20 to move from the second position,
shown in FIG. 2, to
the first position, shown in FIG. 1, to place the brake pipe passageway 16 in
fluid
communication with the brake cylinder passageway 18 via the valve passageway
42. The
amount of air from the brake pipe passageway 16 to the brake cylinder
passageway 18 is
determined by the amount of brake cylinder leakage. Further, the size of the
first through hole
44 and the second through hole 46 may also act as a choke to control the rate
at which brake pipe
flows to the brake cylinder passageway 18. For service brake applications
where there is no
leakage out of the brake cylinder, the brake cylinder pressure is developed to
within an
acceptable tolerance of the target cylinder pressure, the valve member 20
moves the second
position (FIG. 2) to isolate the brake pipe passageway 16 from the brake
cylinder passageway
18. The backflow check valve 50 prevents brake cylinder air from feeding into
the brake pipe
passageway 16 in the event that brake pipe pressure becomes lower than brake
cylinder pressure.
[0031] When the brake application is released, the brake cylinder passageway
18 is exhausted
to atmosphere causing the second check valve 64 to move from the second
position to the first
position thereby exhausting the reference chamber 74 along with the brake
cylinder
passageway 18.
[0032] While several embodiments were described in the foregoing detailed
description, those
skilled in the art may make modifications and alterations to these embodiments
without
departing from the scope and spirit of the invention. Accordingly, the
foregoing description is
intended to be illustrative rather than restrictive.
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