BENDIX SR-7 SPRING BRK MODULATING VALVE User guide

1
®
Bendix®SR-7™Spring Brake Modulating Valve
SD-03-9043
DESCRIPTION
TheBendix®SR-7™springbrakemodulatingvalveisusedin
conjunction with a dual air brake system and spring brake
actuatorand performs thefollowing functions:
1. Providesarapidapplicationof the springbrakeactuator
whenparking.
2. Modulatesthespring brake actuator application using
the dual brake valve should a primary failure occur in
the service brake system.
3. Preventscompoundingof service andspring forces.
The valve has one park control, one service control, one
supply, one balance, four delivery NPTF ports, and an
exhaustportprotectedbyanexhaustdiaphragm. Thevalve
incorporatestwo mountingstuds formounting the valve to
theframe rail orcross member(where applicable).
MOUNTING
STUDS (2)
EXHAUST
42
CONTROL
PORT
2
DELIVERY
1
SUPPLY
PORT
41
BALANCE
PORT
FIGURE 1 - EXTERIOR VIEW
3
EXHAUST
2
DELIVERY
4-1
PARK CONTROL
(FROM DASH
VALVE)
PIPE PLUG
(INCLUDED IN
QUICK RELEASE
VALVE
APPLICATIONS)

2
OPERATION
The operation guidelines shown in this manual represent
the relay valve based SR-7™(refer to system schematic
shown in figure 3). Aquick release based valve functions
similarlytothe relayvalvebased version withthe exception
PARK CONTROL
PORT
SUPPLY PORT
INLET / EXHAUST
VALVE
MAIN PISTON
CONTROL PISTON
SPRING GUIDE
RETAINING RING
MAIN PISTON SPRING
SPACER
STATIC PISTON
STATIC PISTON
SPRING
O-RING
O-RING
O-RING
UPPER BODY
VALVE RETAINER
SPRING
LOWER BODY
SPRING
CHECK VALVE
GUIDE
O-RING
O-RING
DOUBLE CHECK
VALVE O-RING
CHECK VALVE
COVER
DIAPHRAGM WASHER
RETAINING RING
VALVE SEAT
DIAPHRAGM
#10 TORX HEAD SCREW
RETAINING RING
O-RING
O-RING
EXHAUST
PORT
FIGURE2-SECTIONALVIEWOFSR-7™SPRINGBRAKEMODULATINGVALVE USED INRELAYVALVEAPPLICATIONS
IN-LINE SINGLE
CHECK VALVE
SPRING
BALL CHECK
VALVE
O-RING
O-RING
O-RING
O-RING
LOWER VALVE
GUIDE
1/4-20 MACHINE
SCREWS
that all air delivered to spring brakes passes through the
parkcontrolportthrough thein-linesinglecheck valve. The
SR-7™quick release style can be easily identified by the
pipeplug inthe supplyport ofthe valve.

3
PP-DC™
VALVE
SYSTEM FOR A 4X2 OR 6X4
STRAIGHT TRUCK WITH
PP-DC PARKING CONTROL
™
SR-7 Valve w/single check
Ref: 5010914
™
FIGURE 3 - SYSTEM SCHEMATIC WITH PP-DC™PARK CONTROL
FIGURE 4 - SYSTEM SCHEMATIC WITH PP-1™PARK CONTROLAND DC-4™DOUBLE CHECK VALVE
SYSTEM FOR A 4X2 OR 6X4
STRAIGHT TRUCK WITH
PP-1 PARKING CONTROL
™
PP-1
VALVE
™
SR-7 valve
w/o single check
™
DC-4™
VALVE

4
CHARGING SPRING BRAKE ACTUATORS
BELOW 107 PSI (FIGURE 5)
With the air brake system charged and the parking brakes
released (by pushing the dash valve button in), air enters
theparkcontrol port. This openstheSR-7™valvetosupply
air pressure to the spring brake chambers. As illustrated,
air pressure in the chambers is below 107 psi (nominally).
CHARGINGSPRING BRAKEACTUATORSABOVE
107 PSI (FIGURE 6)
Once the SR-7™valve delivery pressure reaches 107 psi
(nominal), the inlet and exhaust are closed (valve lap
position). Thismaintainsthe spring brakehold-offpressure
at107 psi(nominal).
BALANCE PORT
SECONDARY RESERVOIR
CONSTANT PRESSURE
FIGURE 5 - CHARGING LESS THAN 107 PSI
à
CONTROL LINE PRESSURE
DELIVERY TO SPRING BRAKES
INLET / EXHAUST VALVE OPEN
à
à
à
à
à à
à
à
à
à
CONTROL PORT
FIGURE 6 - CHARGING GREATER THAN 107 PSI
INLET / EXHAUST VALVE SEATED
CONTROL LINE PRESSURE
DELIVERY TO SPRING BRAKES
BALANCE PORT
CONTROL PORT
SECONDARY RESERVOIR
CONSTANT PRESSURE
à
à
à à
à
àà
à

5
NORMAL SERVICE APPLICATION (FIGURE 7)
Duringaservice brakeapplication,the valveremainsin the
lapposition. The SR-7™valvemonitors thepresence of air
pressurein bothprimary andsecondary deliverycircuits.
FIGURE7-NORMALSERVICEAPPLICATION
PARKING (FIGURE 8)
Actuatingthe parkbrakes (by pulling the dashvalve button
out)exhausts springbrake airpressure throughthe SR-7™
valveexhaustport.
FIGURE 8 - PARKING
INLETVALVE SEATED
SECONDARY RESERVOIR
CONSTANT PRESSURE
CONTROL LINE PRESSURE
AIR EXHAUSTS FROM
SPRING BRAKES
CONTROL PORT
MAIN AND CONTROL PISTONS MOVE UP
à
à
à
à
à
à
BALANCE PORT
à
à
à
à
SECONDARY RESERVOIR
CONSTANT PRESSURE
CONTROL LINE PRESSURE
BALANCE PORT - PRIMARY
CIRCUIT PRESSURE
CONTROL PORT - SECONDARY
CIRCUIT PRESSURE
INLET / EXHAUST VALVE SEATED
DELIVERY TO SPRING BRAKES
à
à
à
à
à
à
à
à
à
à

6
à
SERVICE APPLICATION WITH LOSS OF AIR IN
PRIMARY CIRCUIT (FIGURE 9)
Withtheparking brakes released(dashvalve button in)and
the absence of air in the primary circuit delivery, a service
brake application from the secondary circuit causes the
pressureinthespringbrakesto be exhaustedproportionally
tothisapplication. Thisisknownasspringbrakemodulation.
A 30 psi service brake application will exhaust the spring
brakepressure to approximately60 psi.
SECONDARY RESERVOIR
CONSTANT PRESSURE
AIR EXHAUSTS FROM
SPRING BRAKES
FIGURE 9- SERVICEAPPLICATION LOSSOFPRIMARYCIRCUIT
INLET VALVE SEATED
CONTROL LINE PRESSURE
BALANCE PORT - LOSS OF
PRIMARY CIRCUIT PRESSURE
CONTROL PORT - SECONDARY
CIRCUIT PRESSURE
SECONDARY RESERVOIR
NO PRESSURE
CONTROL LINE PRESSURE
DELIVERY TO
SPRING BRAKES
CONTROL PORT - LOSS OF
SECONDARY CIRCUIT PRESSURE
à
à
à
à
à
à
à
à
à
à
à
à à
MAIN PISTON MOVES UP
à
à
à
à
à
à
à
à
à
à
à à
BALANCE PORT - PRIMARY
CIRCUIT PRESSURE
SERVICE APPLICATION WITH LOSS OF AIR IN
SECONDARY CIRCUIT (FIGURE 10)
Withtheparkingbrakes released (dashvalvebuttonin) and
the absence of air in the secondary circuit reservoir, the
externalsinglecheckvalveinthesupplyportsealstoprevent
airleakageto atmospherefromthe SR-7™valve. Thedash
valvedeliveryairflowsthroughthein-linesinglecheckvalve
andbecomesSR-7™valve supplyair. This airisdelivered to
maintain at least 107 psi (nominal) in the spring brake
chambers.
FIGURE 10 - SERVICEAPPLICATION LOSS OF SECONDARY CIRCUIT
à
IN-LINE SINGLE
CHECK VALVE
à
à
à
à

7
ANTI COMPOUNDING (FIGURE 11)
TheSR-7™valveprovidesanti-compoundingoftheserviceand
spring brake forces. When the park brakes are actuated
(by pulling the dash valve button out), a service brake
applicationwillcausetheSR-7™valvetodeliverairpressure
to the spring brake chambers. Thus the vehicle is held
stationary using a service brake application. When the
servicebrake application isreleased, thedeliverypressure
isexhaustedfromthespringbrakechambersandthevehicle
remainsparked usingthe springbrake actuators.
PREVENTIVE MAINTENANCE
Important: Review the Bendix Warranty Policy before
performinganyintrusivemaintenanceprocedures.Awarranty
maybevoided if intrusivemaintenance is performedduring
thewarrantyperiod.
No two vehicles operate under identical conditions; as a
result, maintenance intervals may vary. Experience is a
valuableguideindeterminingthe best maintenanceinterval
forairbrake systemcomponents.Ata minimum, theSR-7™
valveshouldbeinspectedevery6monthsor1500operating
hours,whichever comesfirst, for proper operation. Should
the SR-7™valve not meet the elements of the operational
testsnotedinthisdocument,furtherinvestigationandservice
ofthevalve may berequired.
OPERATING TEST
Blockvehicleand hold bymeansother than vehiclebrakes.
Chargeair brake systemto governorcut-out pressure.
1. Placeparking control valve in “park”position. Observe
that spring brake actuators apply promptly. Remove
onelinefrom delivery portoftheSR-7™valveand install
testgaugeknown tobeaccurate. Place parking control
valve in “release” position. Observe that spring brake
actuatorsrelease fully.
2. With parking control valve in “release” position, note
gaugepressurereading. (Correctspring brake actuator
hold-offpressure is 107 psinominally.)
3. Place parking control valve in “park” position - gauge
readingshould dropto zeropromptly. Alag(more than
3 seconds) in drop of pressure would indicate faulty
operation.
4. With the parking control valve in the “park” position,
gradually apply foot brake valve and note a pressure
reading increase on the gauge installed in the SR-7™
valvedeliveryport.
5. Placeparking control valve in “release” position.
6. Drain thereservoir,whichsuppliestherearservicebrake
circuit,applythefootbrake valve several timesandnote
that pressure reading on gauge decreases each time
foot brake valve is applied (spring brake modulation).
Afterthefootbrakevalvehasbeenappliedseveraltimes,
pressureon gauge willdrop to the point where release
of the spring brake actuators will no longer occur.
FIGURE 11 -ANTI-COMPOUNDING
NO CONTROL LINE
PRESSURE
SECONDARY RESERVOIR
CONSTANT PRESSURE
BALANCE PORT -
PRIMARY CIRCUIT PRESSURE
CONTROL PORT -
SECONDARY CIRCUIT PRESSURE
INLET / EXHAUST VALVE OPEN
DELIVERY TO SPRING BRAKES
à
à
à
à
à à
à
à
à
à
à
à
à
à
à
à
à

8
LEAKAGE TEST
Placethe parkcontrol valvein the“release” position;using
asoap solution,coat allportsincluding theexhaust port. A
1" bubble in 3 seconds is permitted (175 SCCM).
If the valve does not function as described, or if leakage is
excessive,itis recommended thatitbe replacedwithanew
orremanufacturedunit available fromaBendix parts outlet.
DO NOT ATTEMPT TO DISASSEMBLE THE SR-7™
VALVE. THE VALVE CONTAINS HIGH SPRING FORCES
THAT COULD RESULT IN PERSONAL INJURY IF
DISASSEMBLYISATTEMPTED!
SERVICING THE SR-7™VALVE
WARNING! PLEASE READ AND FOLLOW
THESE INSTRUCTIONS TO AVOID
PERSONAL INJURYOR DEATH:
When working on or around a vehicle, the following
general precautions should be observed at all times.
1. Park the vehicle on a level surface, apply the
parking brakes, and always block the wheels.
Always wear safety glasses.
2. Stop the engine and remove ignition key when
working under or around the vehicle. When
working in the engine compartment, the engine
should be shut off and the ignition key should be
removed. Where circumstances require that the
enginebeinoperation, EXTREME CAUTION should
be used to prevent personal injury resulting from
contact with moving, rotating, leaking, heated or
electrically charged components.
3. Do not attempt to install, remove, disassemble or
assemble a component until you have read and
thoroughly understand the recommended
procedures. Useonly the proper tools and observe
all precautions pertaining to use of those tools.
4. If the work is being performed on the vehicle’s air
brake system, or any auxiliary pressurized air
systems,makecertainto drain the air pressure from
all reservoirs before beginning ANY work on the
vehicle. If the vehicle is equipped with an AD-IS™
air dryer system or a dryer reservoir module, be
sure to drain the purge reservoir.
5. Following the vehicle manufacturer’s
recommendedprocedures,deactivatetheelectrical
system in a manner that safely removes all
electrical power from the vehicle.
6. Never exceed manufacturer’s recommended
pressures.
7. Never connect or disconnect a hose or line
containing pressure; it may whip. Never remove a
component or plug unless you are certain all
system pressure has been depleted.
8. Use only genuine Bendix®replacement parts,
components and kits. Replacement hardware,
tubing, hose, fittings, etc. must be of equivalent
size, type and strength as original equipment and
be designed specifically for such applications and
systems.
9. Components with stripped threads or damaged
parts should be replaced rather than repaired. Do
not attempt repairs requiring machining or welding
unless specifically stated and approved by the
vehicle and component manufacturer.
10. Prior to returning the vehicle to service, make
certainallcomponentsandsystemsarerestoredto
their proper operating condition.
VALVE REMOVAL
1. Prior to removing the SR-7™valve, apply the parking
brakesand drainall thevehicle reservoirs.
2. Identifyall airlines before disconnecting.
3. Removethe twomounting nuts thatsecure thevalve to
theframerail andremovethe valve.
VALVE INSTALLATION
1. Align the mounting studs with the mounting holes on
the vehicle frame rail. Tighten the mounting nuts to
180-220in. lbs.
2. Install the valve onto the vehicle ensuring all ports are
connectedas marked duringdisassembly.
TESTING THE REPLACEMENT SR-7™SPRING
BRAKE MODULATING VALVE
Performoperatingandleakagetestsasoutlinedin“Operating
Tests” section.
BW2271 © 2004 Bendix Commercial Vehicle Systems LLC 3/2004. Printed in U.S.A. All rights reserved.