BENDIX DOUBLE CHECK VALVES User manual

1
SD-03-2202
OPERATION
Asairunderpressureenterseitherendofthedoublecheck
valve(inlet port) the movingshuttle or disc respondsto the
pressure and seals the opposite port, assuming it is at a
lower pressure level than the other. The air flow continues
outthedeliveryportofthedoublecheckvalve.Theposition
of the shuttle or disc will reverse if the pressure levels are
reversed. Double check valves are designed so that the
shuttle or disc can never impede the backflow of air in the
exhaustmode.
Figure 3 (see page 2) illustrates a typical use of a double
checkvalvetocontrolagivendevice, suchastrailerbrakes,
fromeither of two controlsources.
Figure 4 (see page 2) illustrates a typical use of a double
checkvalve to supply air to a system or systemsfromeither
oftwoseparatesources,whicheverisatthegreaterpressure
level. In this type of installation the pressure differential to
which the valve is subjected may under certain conditions
be minimal. It is therefore suggested that performance of
the double check valve will be optimized if it is mounted in
thehorizontalposition.
DESCRIPTION
Double check valves are used in an air brake system to
direct a flow of air into a common line from either of two
sources,whichever is at the higherpressure. They may be
used for directing air flow for specific functions or to select
the higher pressure of either of two sources of air as a
supplysource.
Bendix manufactures two types of double check valves:
shuttleanddisc. Althoughthevalvesare somewhatdifferent
physically, the same function is performed by both types.
The difference in the design of the two valves is that the
shuttle type has a movable shuttle to seal off the lower
pressuresource, whereasthedisctype has amovabledisc.
Bendix®Double Check Valves
FIGURE1-DC-4
™
DOUBLECHECKVALVE(SHUTTLETYPE) FIGURE 2 - DOUBLE CHECK VALVE (DISC TYPE)
DELIVERY
SUPPLY
SUPPLY
SHUTTLE
GUIDE
BODY
O-RING
SUPPLY
DELIVERY SHUTTLE
VALVE VALVE
DISC
VALVE
GUIDE BODY
CAP
O-RING
DELIVERY
SUPPLY
CAP

2
Reservoir
Brake Valve
Trailer Hand
Control Valve
SERVICE CHECKS
OPERATING AND LEAKAGE TEST
A. Whenthe doublecheckvalveis usedinconjunctionwith
atrailercontrolvalve,thefollowingoperatingandleakage
test can be made:
1. Applyandreleasefoot brake valve and note thatthe
brakesapplyandreleaseonbothtractor and trailer.
2. Apply and release the trailer control valve and note
that only the trailer brakes apply and release. With
trailer control valve applied check exhaust port of
foot brake valve for leakage with soap solution.
Permissibleleakageisa1” bubblein5 seconds(100
sccm).
3. Apply and hold a full foot brake valve application.
Checkexhaustportoftrailercontrolvalveforleakage
with soap solution. Permissible leakage is a 1”
bubble in 5 seconds (100 sccm). (Note: On some
vehicles,anexhaustlineis connectedtothe exhaust
port and piped outside the cab in which case it may
benecessarytodisconnect thislineto makeleakage
check.)
B. Ifthe double check valveistobebenchtestedor tested
on the vehicle, two separately controlled air supplies
must be connected to the inlet ports.
1. Installan accurate test gaugein the outlet portor in
a line from outlet port.
2. Apply and release air to one inlet port and note that
gaugeregistersapplicationandrelease.
3. Repeat by applying and releasing air to other inlet
port.
4. Leakagecheck should be performed at inlet ports of
valvein thefollowingmanner:
a. Disconnect the line from one inlet port.
b. Apply air to other inlet port and coat opposite
inletportwithsoapsolution.Permissibleleakage
is a 1” bubble in 5 seconds (100 sccm).
c. Repeat Step “b” applying air to other inlet port
whilechecking opposite inlet port forleakage.
Ifthe doublecheckvalve doesnotfunctionas describedorif
leakage is excessive, it is recommended that the valve be
repairedorreplacedwithgenuineBendixparts. Thefollowing
instructionsshould prove helpful:
DISASSEMBLY
1. Removethe end cap(s)fromthevalve.
2. Removethe grommets (if applicable).
3. Remove the shuttle and/or shuttle guide, disc and/or
discguide (depending upon type of valve).
PREVENTIVE MAINTENANCE
Important: Review the Bendix Warranty Policy before
performinganyintrusivemaintenanceprocedures.Awarranty
maybe voided if intrusive maintenance is performed during
thewarranty period.
No two vehicles operate under identical conditions; as a
result, maintenance intervals may vary. Experience is a
valuableguide in determiningthebestmaintenance interval
forair brake system components.Ataminimum,theDC-4™
valveshouldbeinspected every6months or1500operating
hours,whichever comes first, for proper operation. Should
the DC-4™valve not meet the elements of the operational
testsnotedinthisdocument,furtherinvestigationandservice
ofthe valve may be required.
Reservoir
Reservoir
Trailer Supply
Spring Brake Control
Double Check
Valve
FIGURE 4 - DOUBLE CHECK VALVE: SYSTEM WITH TWO
SUPPLY SOURCES
PP-7™
Valve
PP-1™
Valve
FIGURE 3 - DOUBLE CHECK VALVE: CONTROL OF
SYSTEM FROM EITHER OF TWO CONTROL SOURCES
Double
Check
Valve
ToTrailer
Brakes

3
CLEANING AND INSPECTION
1. Clean all metal parts in mineral spirits and dry them
completely.
2. Inspect all parts for excessive wear or deterioration.
Inspectvalve seats for nicks orburrs.
3. Inspecttheboresofthevalve housing for deep scuffing
orgouges.
Replace all parts that were discarded and any parts not
foundtobeserviceableduringinspection,usingonlygenuine
Bendixreplacementparts.
ASSEMBLY
BeforeassemblingtheDC-4™valve,lubricate allo-ringsand
o-ringgrooveswithBendixsiliconelubricant(Pc.No.291126)
orequivalent.
NOTE: When using pipe thread sealant during assembly
andinstallation, take particular care toprevent the
sealant from entering the valve itself. Apply the
sealantbeginningwiththe secondthreadback from
theend.
1. Install the disc guide, disc and/or shuttle and shuttle
guide.
2. Coat all static seals such as o-rings, grommets, etc.
with BW 650M Silicone lubricant (BW 291126). It is not
necessary to lubricate shuttles or discs.
3. Installthegrommets.
4. Install the end cap(s).
TESTINGOF REBUILT DOUBLE CHECKVALVE
Performoperatingandleakagetestsasdescribedin“Service
Checks” section.
GENERAL SAFETY GUIDELINES
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
enginebe inoperation, EXTREMECAUTION 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 andobserve
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, make certain to 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
recommended procedures, deactivate the
electrical 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
notattempt repairs requiring machiningor welding
unless specifically stated and approved by the
vehicle and component manufacturer.
10. Prior to returning the vehicle to service, make
certain all components and systems are restored
to their proper operating condition.
11. For vehicles with Antilock Traction Control (ATC),
theATC function must be disabled (ATC indicator
lampshould be ON)prior to performingany vehicle
maintenance where one or more wheels on a
drive axle are lifted off the ground and moving.

4BW1582 © 2007 Bendix Commercial Vehicle Systems LLC. All rights reserved. 3/2007 Printed in U.S.A.