BENDIX TU-FLO 550 COMPRESSOR User manual

SD-01-333
Bendix®Tu-Flo®550 Air Compressor
BENDIX®TU-FLO®550 AIR COMPRESSOR
(CROSS SECTION)
BENDIX®TU-FLO®550 AIR COMPRESSOR
(EXTERIOR)
AIR DISCHARGE WATER OUTLET
PIECE NO.
TAG
GOVERNOR
MOUNTING
PAD
CRANKCASE
PISTON RINGS
PISTON
CRANKSHAFT
CONNECTING
ROD
INLET VALVE
SEAT
UNLOADER
INLET VALVE
CYLINDER
HEAD
END VIEW OF CYLINDER HEAD
DISCHARGE
VALVE SPRING
DISCHARGE
VALVE
DISCHARGE
VALVE STOP
AIR INLET
CRANKCASE
INLET
INLET VALVE
SPRING
DESCRIPTION
The function of the air compressor is to provide and
maintain air under pressure to operate devices in the air
brakeand/orauxiliaryairsystems.TheBendix®Tu-Flo®550
compressor is a two cylinder single stage, reciprocating
compressor with a rated displacement of 13.2 cubic feet
per minute at 1250 RPM.
The compressor assembly consists of two major
subassemblies, the cylinder head and the crankcase. The
cylinder head is an iron casting which houses the inlet,
discharge, and unloader valving. (See Figure 1.) The
cylinder head contains the air inlet port and is designed
with both top and side air discharge ports. Three water
coolant ports provide a choice of coolant line connections.
Governormounting surfacesare providedat boththe front
and the rear of the cylinder head. The head is mounted
on the crankcase and is secured by six cap screws. The
Tu-Flo®550 compressor is designed suchthat the cylinder
headcan be installedin one of twopositions which are180
degrees apart. The crankcase houses the cylinder bores,
pistons, crankshaft and main bearings, and provides the
flange or base mounting surface.
DISCHARGE
VALVE SEAT
UNLOADER
COVER
WATER
INLET

OPERATION
The compressor is driven by the vehicle engine and
is operating continuously while the engine is running.
Actual compression of air is controlled by the compressor
unloading mechanism and the governor. The governor
which is generally mounted on the compressor maintains
the brake system air pressure to a preset maximum and
minimum pressure level.
INTAKE AND COMPRESSION OF AIR (LOADED)
During the down stroke of the piston, a slight vacuum is
createdbetweenthetopofthepistonandthecylinderhead,
causingtheinlet valve tomove offitsseat and open.(Note:
The discharge valve remains on its seat.)Atmospheric air
is drawn through the air strainer and the open inlet valve
into the cylinder (see Figure 4). As the piston begins its
upward stroke, the air that was drawn into the cylinder on
the down stroke is being compressed.Air pressure on the
inlet valve plus the force of the inlet spring, returns the
inlet valve to its seat and closes. The piston continues the
upward stroke and compressed air pushes the discharge
valveoffitsseat and airflows by the open dischargevalve,
intothe discharge line and tothe reservoirs (see Figure 5).
Asthe piston reaches the top of itsstroke and starts down,
thedischargevalvespringandairpressureinthedischarge
line returns the discharge valve to its seat. This prevents
the compressed air in the discharge line from returning to
the cylinder bore as the intake and compression cycle is
repeated.
CAT MACK
(MACK STYLE)
DETROIT
DIESEL
AIR INLET
WATER
UNLOADER COVER
PLATE
AIR DISCHARGE
WATER
AIR
DISCHARGE
GOVERNOR
WATER
MANUFACTURED BY BENDIX
TU-FLO®550 COMPRESSOR
BENDIX NO.
SERIAL NO.
MACK
"FOXHEAD" CUMMINS
MACK
EXTENDED
FIGURE 2 - FLANGE CONFIGURATIONS
Various mounting and drive configurations, as shown in
Figure 2, are supplied as required by the vehicle engine
designs. A nameplate identifying the compressor piece
number and serial number is attached to the side of the
crankcase. (Reference Figure 3.)
FIGURE 3 - NAMEPLATE
FIGURE 1 - CYLINDER HEAD
CAT BASE
MOUNT

forcethe pistons upwardand the inlet valves returnto their
seats. Compression is then resumed.
COMPRESSOR & THE AIR BRAKE SYSTEM
GENERAL
The compressor is part of the total air brake system, more
specifically, the charging portion of the air brake system.
As a component in the overall system its condition, duty
cycle, proper installation and operation will directly affect
other components in the system.
Powered by the vehicle engine, the air compressor builds
theairpressurefortheair brakesystem.Theaircompressor
istypically cooled bythe engine coolantsystem, lubricated
by the engine oil supply and has its inlet connected to the
engine induction system.
As the atmospheric air is compressed, all the water vapor
originally in the air is carried along into the air system, as
well as a small amount of the lubricating oil as vapor. If an
air dryer is not used to remove these contaminants prior
to entering the air system, the majority, but not all, will
condense in the reservoirs. The quantity of contaminants
that reach the air system depends on several factors
including installation, maintenance and contaminant
handling devices in the system. These contaminants must
eitherbe eliminated priorto entering the air systemor after
they enter.
DUTY CYCLE
The duty cycle is the ratio of time the compressor spends
buildingairtothetotalenginerunningtime.Aircompressors
are designed to build air (run "loaded") up to 25% of the
time. Higher duty cycles cause conditions that affect air
GOVERNOR
PORT
AIR
INLET
PORT
INLET
VALVE
OPEN
PISTON
MOVING
DOWN
DISCHARGE
VALVE
CLOSED
GOVERNOR
PORT
INLET
VALVE
CLOSED
PISTON
MOVING
UP
FIGURE 4 - OPERATIONAL-LOADED (INTAKE)
FIGURE 5 - OPERATIONAL-LOADED (COMPRESSION)
GOVERNOR
PORT
DISCHARGE
PORT
AIR
INLET
PORT
FIGURE 6 - OPERATIONAL-UNLOADED
DISCHARGE
VALVE
CLOSED
DISCHARGE
VALVE
OPEN
AIR
INLET
PORT
NON-COMPRESSION OF AIR (UNLOADED)
When air pressure in the reservoir reaches the cut-out
setting of the governor, the governor allows air to pass
fromthe reservoir, throughthe governor andinto the cavity
above the unloader pistons. The unloader pistons move
down holding the inlet valves off their seats (see Figure
6.)
With the inlet valves held off their seats by the unloader
pistons, air is pumped back and forth between the two
cylinders, and the discharge valves remain closed. When
air pressure from the reservoir drops to the cut-in setting
of the governor, the governor closes and exhausts the air
from above the unloader pistons. The unloader springs
INLET VALVE
HELD OPEN
BY UNLOADER
PISTON
AIR
DISCHARGE
PORT
AIR
DISCHARGE
PORT
UNLOADER
PISTON

brake charging system performance which may require
additional maintenance. Factors that add to the duty cycle
are: air suspension, additional air accessories, use of an
undersizedcompressor,frequent stops, excessive leakage
from fittings, connections, lines, chambers or valves, etc.
Refer to TableAin the Troubleshooting section for a guide
to various duty cycles and the consideration that must be
given to maintenance of other components.
COMPRESSOR INSTALLATION
While the original compressor installation is usually
completed by the vehicle manufacturer, conditions of
operation and maintenance may require additional
consideration. The following presents base guidelines.
DISCHARGE LINE
Thedischargeline allows the air,water-vaporand oil-vapor
mixture to cool between the compressor and air dryer or
reservoir. The typical size of a vehicle's discharge line,
(see column 2 of Table A in the Troubleshooting section)
assumesa compressor witha normal (lessthan 25%) duty
cycle,operating in atemperate climate. SeeBendix and/or
other air dryer manufacturer guidelines as needed.
The discharge line must maintain a constant slope down
fromthe compressor tothe air dryerinlet fitting orreservoir
to avoid low points where ice may form and block the flow.
If, instead, ice blockages occur at the air dryer or reservoir
inlet, insulation may be added here, or if the inlet fitting is
a typical 90 degree fitting, it may be changed to a straight
or 45 degree fitting. Shorter discharge line lengths or
insulation may be required in cold climates.
While not all compressors and charging systems are
equippedwitha discharge line safetyvalvethis component
is recommended. The discharge line safety valve is
FIGURE 6A - SYSTEM DRAWING
FIGURE 6B - DISCHARGE LINE SAFETY VALVE
HOLE
THREAD
installed in the cylinder head (Tu-Flo®550/750) or close to
the compressor discharge port and protects against over
pressurizing the compressor in the event of a discharge
line freezeup.
DISCHARGE LINE TEMPERATURE
When the temperature of the compressed air that enters
the air dryer is within the normal range, the air dryer can
removemost of the charging systemoil. If the temperature
of the compressed air is above the normal range, oil as
oil-vapor is able to pass through the air dryer and into the
air system. Larger diameter discharge lines and/or longer
discharge line lengths can help reduce the temperature.
The air dryer contains a filter that collects oil droplets, and
a desiccant bed that removes almost all of the remaining
water vapor. The compressed air is then passed to the air
brake service (supply) reservoir. The oil droplets and the
watercollectedareautomatically purged when the governor
reaches its "cut-out" setting.
Air Dryer
Reservoir Drain
Service Reservoir
(Supply Reservoir)
Compressor
Governor
(Governor plus Synchro valve
for the Bendix®DuraFlo™596
Compressor)
Discharge
Line Optional “Ping” Tank
Optional Bendix®PuraGuard QC™
Oil Coalescing Filter
The Air Brake Charging System supplies the
compressedairfor the braking systemaswell as other air
accessories for the vehicle. The system usually consists
of an air compressor, governor, discharge line, air dryer,
and service reservoir.

FIGURE 7 - LUBRICATION
OIL
INLET
2. Naturally aspirated Engine Air Cleaner - Compressor
inlet is connected to the engine air cleaner or the
vacuum side (engine air cleaner) of the supercharger
or turbocharger.
3. Pressurized induction - Compressor inlet is
connected to the pressure side of the supercharger or
turbocharger.
Seethe tabulated technical dataon page 14of this manual
for specific requirements for numbers 2 and 3 above.
If a previously unturbocharged compressor is being
turbocharged,itisrecommendedthattheinletcavityscreen
(238948)be installed with aninlet gasket (291909)on both
sides of the screen.
WATER
IN
OR
(1 PORT
ONLY)
WATER
OUT
OR
(1 PORT
ONLY)
WATER OUT
WATER
OUT
WATER
IN
WATER
IN
FIGURE 8 - COOLING
For vehicles with accessories that are sensitive to small
amounts of oil, we recommend installation of a Bendix®
PuraGuard®QC™oilcoalescingfilter,designedtominimize
the amount of oil present.
LUBRICATION
The vehicle's engine provides a continuous supply of oil
to the compressor. Oil is routed from the engine to the
compressor oil inlet. An oil passage in the compressor
crankshaft allows oil to lubricate the connecting rod
crankshaft bearings. Connecting rod wrist pin bushings
and crankshaft ball bearings are spray lubricated. An oil
return line connected from the compressor drain outlet
to the vehicle engine crankcase allows for oil return. On
flange mounted models the oil drains back directly to the
engine through the mounting flange.
COOLING
Air flowing through the engine compartment from the
actionof the engine’sfanand the movementof the vehicle
assists in cooling the compressor. Coolant flowing from
the engine’s cooling system through connecting lines
enters the head and passes through internal passages
in the cylinder head and is returned to the engine.
Proper cooling is important in maintaining discharge air
temperatures below the maximum recommended 400
degrees Fahrenheit.
Figure 8 illustrates the various approved coolant flow
connections. See the tabulated technical data in the back
of this manual for specific requirements.
AIR INDUCTION
There are three methods of providing clean air to the Tu-
Flo®550 compressor:
1. Naturally aspirated Local Air Strainer - Compressor
utilizes its own attached air strainer (polyurethane
sponge or pleated paper dry element).

COMPRESSOR TURBOCHARGING
PARAMETERS
Air entering the compressor inlet during the loaded cycle
must not exceed 250 degrees Fahrenheit (121 degrees
Celsius). A metal inlet line is suggested to help meet this
parameter.
The following compressor crankshaft rotative speed and
inlet pressure relationships may not be exceeded.
Crankshaft Maximum Compressor
R.P.M. Inlet Pressure
2200 RPM 30.0 psi (207 kPa)
2600 RPM 25.0 psi (172.5 kPa)
POLYURETHANE SPONGE STRAINER
Every month, 150 operating hours or 5,000 miles,
whichever occurs first, removeand wash allof the parts.
The strainer element should be cleaned or replaced. If the
element is cleaned, it should be washed in a commercial
solvent or a detergent and water solution. The element
should be saturated in clean engine oil, then squeezed
dry before replacing it in the strainer. Be sure to replace
theair strainer gasket if theentire strainer is removed from
the compressor intake.
PAPER AIR STRAINER DRY ELEMENT-PLEATED
POLYURETHANE SPONGE STRAINER
FIGURE 10 - STRAINERS
PREVENTIVE MAINTENANCE
Regularly scheduled maintenance is the single most
important factor in maintaining the air brake charging
system. Refer to Table A in the Troubleshooting section
for a guide to various considerations that must be given
to the maintenance of the compressor and other related
charging system components.
Important Note: Review the warranty policy before
performing any intrusive maintenance procedures. An
extendedwarranty may bevoided if intrusivemaintenance
is performed during this period.
AIR INDUCTION
One of the single most important aspects of compressor
preventive maintenance is the induction of clean air.
The type and interval of maintenance required will vary
depending upon the air induction system used.
The intervals listed under the headings below pertain
to typical highway and street operation. More frequent
maintenance will be required for operation in dusty or
dirty environments.
DRY ELEMENT - PLEATED PAPER STRAINER
Every two months, 800 operating hours or 20,000 miles
whichever occurs first, loosen the spring clip from the
unhinged side of the mounting baffle and open the cover.
Replace the pleated paper filter and secure the cleaned
cover,makingsurethefilteris in position. Be sure to replace
the air strainer gasket if the entire air strainer is removed
from the compressor intake.
0
20
25
15
35
5
30
270024002100180015001200900600
10
Compressor Speed (RPM)
Turbo Limits
40
FIGURE 9 - TURBO LIMITS CURVE
Inlet Pressure (PSIG)

INTAKE ADAPTER
When the engine air cleaner is replaced: Some
compressors are fitted with compressor intake adapters,
which allow the compressor intake to be connected to the
engine air induction system. In this case, the compressor
receives a supply of clean air from the engine air cleaner.
When the engine air filter is changed, the compressor
intakeadapter should bechecked.If it isloose, remove the
intake adapter, clean the strainer plate, if applicable, and
replacetheintake adapter gasket, andreinstall the adapter
securely. Check line connections both at the compressor
intake adapter and at the engine. Inspect the connecting
line for ruptures and replace it if necessary.
COMPRESSOR COOLING
Every 6 months, 1800 operating hours or after each
50,000 miles whichever occurs first, inspect the
compressor discharge port, inlet cavity and discharge line
for evidence of restrictions and carboning. If excessive
buildup is noted, thoroughly clean or replace the affected
parts and closely inspect the compressor cooling system.
Checkallcompressorcoolantlinesforkinks and restrictions
toflow.Minimum coolant line sizeis3/8"I.D.Checkcoolant
lines for internal clogging from rust scale. If coolant lines
appear suspicious, check the coolant flow and compare
to the tabulated technical data present in the back of this
manual. Carefully inspect the air induction system for
restrictions.
LUBRICATION
Every six months,1800 operating hoursor 50,000 miles
whichever occurs first, check external oil supply and
return lines, if applicable, for kinks, bends, or restrictions
to flow. Supply lines must be a minimum of 3/16" I.D. and
return lines must be a minimum of 1/2" I.D. Oil return lines
should slope as sharply as possible back to the engine
crankcase and should have as few fittings and bends as
possible. Refer to the tabulated technical data in the back
of this manual for oil pressure minimum values.
Check the exterior of the compressor for the presence of
oilseepageand refer totheTROUBLESHOOTING section
for appropriate tests and corrective action.
OIL PASSING
All reciprocating compressors currently manufactured will
pass a minimal amount of oil. Air dryers will remove the
majorityofoilpriortoentranceintotheairbrakesystem.For
particularly oil sensitive systems the Bendix®PuraGuard®
QC™oil coalescing filter can be used in conjunction with
a Bendix air dryer.
If compressor oil passing is suspected, refer to the
TROUBLESHOOTING section and TABLE A for the
symptoms and corrective action to be taken. In addition,
Bendix has developed the "Bendix Air System Inspection
Cup" or BASIC test to help substantiate suspected
excessiveoilpassing.Thestepsto be followedwhenusing
the BASIC test are presented in APPENDIX A at the end
of the TROUBLESHOOTING section.
COMPRESSOR DRIVE
Every six months, 1800 operating hours or 50,000
miles,whicheveroccursfirst, checkfornoisycompressor
operation,which could indicate aworn drive gearcoupling,
a loose pulley or excessive internal wear. Adjust and/or
replace as necessary.
If the compressor is belt driven, check for proper belt and
pulley alignment and belt tension. Check all compressor
mounting bolts and retighten evenly if necessary. Check
for leakage and proper unloader mechanism operation.
Repair or replace parts as necessary.
Every 24 months, 7200 operating hours, or after
each 200,000 miles, perform a thorough inspection, and
dependingupontheresultsofthisinspectionorexperience,
disassemble the compressor, clean and inspect all parts
thoroughly, replace all worn or damaged parts using only
genuine Bendix replacements or replace the compressor
with a genuine Bendix remanufactured unit.
GENERAL SERVICE CHECKS
OPERATING TESTS
IN SERVICE OPERATING TESTS
Compressor Performance: Build-up Test
This test is performed with the vehicle parked and the
engine operating at maximum recommended governed
speed. Fully charge the air system to governor cut out (air
dryer purges). Pump the service brake pedal to lower the
system air pressure below 80 psi using the dash gauges.
As the air pressure builds back up, measure the time
from when the dash gauge passes 85 psi to the time it
passes 100 psi. The time should not exceed 40 seconds.
If the vehicle exceeds 40 seconds, test for (and fix) any
air leaks, and then re- test the compressor performance.
If the vehicle does not pass the test the second time,
use the Advanced Troubleshooting Guide for Air Brake
Compressors, starting on page A-1 of this document to
assist your investigation of the cause(s).
Note: All new vehicles are certified using the FMVSS
121 test (paragraph S5.1.1) by the vehicle manufacturer,
however the above test is a useful guide for in-service
vehicles.
Optional Comparative Performance Check
It may be useful to also conduct the above test with the
enginerunning athigh idle(instead ofmaximum governed

speed), and record the time taken to raise the system
pressure a selected range (for example, from 90 to 120
psi, or from 100 to 120 psi, etc.) and record it in the
vehicle’s maintenance files. Subsequent build-up times
throughoutthe vehicle’s service lifecan then be compared
to the first one recorded. (Note: the 40 second guide in
the test above does not apply to this build-up time.) If the
performance degrades significantly over time, you may
use the Advanced Troubleshooting Guide for Air Brake
Compressors, starting on page A-1 of this document, to
assist investigation of the cause(s).
Note: When comparing build-up times, be sure to make
anallowance for anyair system modificationswhich would
cause longer times, such as adding air components or
reservoirs. Always check for air system leakage.
AIR LEAKAGE TESTS
Compressor leakage tests need not be performed on a
regular basis. These tests should be performed when; it
is suspected that discharge valve leakage is substantially
affecting compressor build-up performance, or when it is
suspectedthatthe compressor is “cycling”betweentheload
and unloaded modes due to unloader piston leakage.
These tests must be performed with the vehicle parked
on a level surface, the engine not running, the entire air
system completely drained to 0 P.S.I., and the inlet check
valve detail parts removed, if applicable.
UNLOADER PISTON LEAKAGE
Theunloaderpistonscanbecheckedforleakageasfollows:
with the cylinder head removed from the compressor and
the inlet flange securely covered, apply 120 psi of air
pressure to the governor port. Listen for an escape of air
at the inlet valve area.An audible escape of air should not
be detected.
DISCHARGE VALVE LEAKAGE
Unloader piston leakage must be repaired before this test
is performed. Leakage past the discharge valves can be
detected as follows: Remove the discharge line and apply
shop air back through the discharge port. Listen for an
escapeofairatthecompressorinletcavity.Abarelyaudible
escape of air is generally acceptable.
If the compressor does not function as described above
or if the leakage is excessive, it is recommended that it be
returned to the nearest authorized Bendix distributor for a
factory remanufactured compressor. If it is not possible,
the compressor can be repaired using a genuine Bendix
cylinder head maintenance kit. Retest the cylinder head
after installation of the kit.
REMOVAL AND DISASSEMBLY
GENERAL
The following disassembly and assembly procedure is
presented for reference purposes and presupposes that
a major rebuild of the compressor is being undertaken.
Severalmaintenancekitsareavailablewhichdonotrequire
full disassembly. The instructions provided with these
parts and kits should be followed in lieu of the instructions
presented here.
REMOVAL
These instructions are general and are intended to be
a guide, in some cases additional preparations and
precautions are necessary.
1. Block the wheels of the vehicle and drain the air
pressure from all the reservoirs in the system.
2. Drain the engine cooling system and the cylinder head
ofthe compressor. Identifyand disconnect allair, water
and oil lines leading to the compressor.
3. Remove the governor and any supporting bracketry
attached to the compressor and note their positions
on the compressor to aid in reassembly.
4. Remove the discharge and inlet fittings, if applicable,
and note their position on the compressor to aid in
reassembly.
5. Removethe flange or basemounting bolts and remove
the compressor from the vehicle.
6. Removethedrivegear(s)orpulleyfromthecompressor
crankshaftusingagearpuller.Inspectthepulleyorgear
andassociated parts forvisible wear ordamage. Since
these parts are precision fitted, they must be replaced
if they are worn or damaged.
PREPARATION FOR DISASSEMBLY
Remove road dirt and grease from the exterior of the
compressorwithacleaningsolvent.Beforethecompressor
is disassembled, the following items should be marked to
showtheirrelationshipwhenthecompressor is assembled.
Mark the rear end cover in relation to the crankcase.
Mark the base plate or base adapter in relation to the
crankcase.
A convenient method to indicate the above relationships
is to use a metal scribe to mark the parts with numbers or
lines. Do not use marking methods such as chalk that can
be wiped off or obliterated during rebuilding.
CYLINDER HEAD
Remove the six cylinder head cap screws (1) and tap the
head with a soft mallet to break the gasket seal. Remove
the unloader cover plate cap screws (2), lockwashers (3)
and the unloader cover plate (4). Scrape off any gasket
41

material (5) from the cover plate, cylinder head and
crankcase.
1. Remove the unloader pistons (7), o-rings (6) and
springs (8).
2. Inspect the unloader piston bushings (9) for nicks,
wear, corrosion and scoring. It is recommended that
the compressor be replaced if it is determined that the
unloader bushing is damaged or worn excessively.
Before disassembling the discharge valve mechanism,
measureandrecordthedischargevalvetravel(fromclosed
to completely open).
3. If the measured discharge valve travel exceeds .046
inches, the compressor should be replaced. If the
discharge valve travel does not exceed .046, using a
9/16"Allen wrench, remove the discharge valve seats
(18), valves (17) and valve springs (16).
4. Remove the inlet valve stops (14), valves (17), valve
seats (11), valve springs (12) and gaskets (10). It is
recommendedthatatoolsuchasaJ-25447-B,produced
byKentMooreTool DivisionRoseville, Michigan phone
1-800-328-6657, be used to remove the inlet valve
stop.
CRANKCASE BOTTOM COVER OR ADAPTER
DISASSEMBLY
1. Removethe cap screws (22)securingthebottom cover
or adapter (21). Tap with a soft mallet to break the
gasket seal. Scrape off any gasket material (20) from
the crankcase and bottom cover or adapter.
CONNECTING ROD DISASSEMBLY
Before removing the connecting rod, mark the connecting
rods(37) and theircaps (39) to ensurecorrect reassembly.
The connecting rod and cap are a matched set therefore
the caps must not be switched or rotated end for end.
1. Removetheconnecting rod bolts (40) andbearingcaps
(39).
2. Push the pistons (26) with the connecting rods
(37) attached out the top of the cylinder bore of the
crankcase.Replacethebearingcapsontheconnecting
rods.
3. Remove the piston rings (23-25) from the piston. If
the piston is to be removed from the connecting rod,
remove the wrist pin Teflon plugs (28) and press the
wrist pin (27) from the piston and connecting rod.
4. If the piston is removed from the rod, inspect the wrist
pin bore in the piston and bronze wrist pin bushing
(36) in the connecting rod. If excessive wear is noted
or suspected, replace the connecting rod and piston.
COMPRESSOR CRANKCASE DISASSEMBLY
1. Remove the key or keys (30) from the crankshaft (29)
andanyburrsfromthecrankshaftwherethekeyorkeys
wereremoved.(Note:Throughdrivecompressorsmay
have a crankshaft key at both ends.)
2. Remove the four cap screws (35) and lockwashers or
nuts and lockwashers that secure the rear end cover
(34) to the crankcase.
3. Removetherear end cover (34), thrust washer(31)and
end cover oil seal ring (33), taking care not to damage
the bearing if present in the end cover.
4. Ifthecompressorhasballtypemain bearings, press the
crankshaft (29) and ball bearings from the crankcase,
then press the ball bearings from the crankshaft.
5. Press the oil seal out of the compressor crankcase, if
so equipped.
CLEANING OF PARTS
GENERAL
All parts should be cleaned in a good commercial grade of
solvent and dried prior to inspection.
CYLINDER HEAD
Remove carbon deposits from the discharge cavity and
rustandscale from the coolingcavitiesof the cylinder head
body.Scrapeallforeign matter fromthe body surfacesand
use shop air pressure to blow the dirt particles from the
cavities. Clean carbon and dirt from the inlet and unloader
passages.Useshopairtoblowthecarbonanddirtdeposits
from the unloader passages.
OIL PASSAGES
Thoroughly clean all oil passages through the crankshaft,
crankcase,endcovers,base plate or base adapter.Inspect
the passages with a wire to be sure. Blow the loosened
foreign matter out with air pressure.
INSPECTION OF PARTS
CYLINDER HEAD BODY
Inspect the cylinder head for cracks or damage. With the
cylinder head and head gasket secured to a flat surface or
crankcase, apply shop air pressure to one of the coolant
ports with all others plugged, and check for leakage by
applying a soap solution to the exterior of the body. If
leakage is detected, replace the compressor.

ITEM QTY DESCRIPTION ITEM QTY DESCRIPTION ITEM QTY DESCRIPTION
1 6 Cylinder Head Cap Screws 16 2 Discharge Valve Spring 31 2 Thrust Washer
2 4 Unloader Plate Cap Screws 17 2 Discharge Valve 32 2 Sleeve (or Ball) Bearing
3 4 Unloader Plate Lock Washers 18 2 Discharge Valve Stop 33 1 End Cover Seal
4 1 Unloader Plate 19 1 Cylinder Head Gasket 34 1 End Cover
5 1 Unloader Plate Gasket 20 1 Base Gasket 35 4 End Cover Cap Screws
6 2 O-ring 21 1 Base Plate 36 2 Wrist Pin Bushing
7 2 Unloader 22 6 Base Plate Cap Screws 37 2 Connecting Rod
8 2 Spring 23 6 Standard Piston Rings 38 2 Conn. Rod Inserts (Sets)
9 2 Unloader Bushing 24 8 Oil Ring 39 2 Connecting Rod Caps
10 2 Gasket 25 4 Expander Ring 40 4 Connecting Rod Bolts
11 2 Inlet Valve Seat 26 2 Piston 41 1 Ball Bearing
12 2 Inlet Valve 27 2 Wrist Pin 42 1 Retaining Ring
13 2 Inlet Valve Spring 28 4 Wrist Pin Button 43 1 Seal
14 2 Inlet Valve Stop 29 1 Crankshaft 44 1 Cotter Pin
15 2 Discharge Valve Stop 30 1 Crankshaft Key 45 1 Locknut
2
4
5
6
7
8
9
BALLBEARING
(MACK EXTENDED
FLANGE)
NAMEPLATE
3
26
23
23
24
25
24 28
27
35
37
33
32
36
11
12
13
14
10
29
3839
40
1
CYLINDER
HEAD
15
16
17
18
19
32
22
21
20
31
CRANKCASE
19
42
44
FLANGE
MOUNT
BASE
MOUNT
32
32
20
CRANKCASE
30 34
24
24
23
25

END COVERS
Check for cracks and external damage. If the crankshaft
main bearing (32) is installed in the end cover (34),
check for excessive wear and flat spots and replace if
necessary.
CRANKCASE
Check all crankcase surfaces for cracks and damage. On
compressors where ball bearing main bearings are used
the difference between the O.D. of the outer race and the
I.D.of the crankcasehole should be .0003in. tight to.0023
in.loose.Thisisto maintain thecorrectfit.Thecompressor
must be replaced if the fit is too loose.
Oncompressorsfittedwithprecision,sleevemainbearings,
the difference between the O.D. of the crankshaft journal
and the main bearing l.D. must not exceed .005 in. If the
clearance is greater than .005 in. the bearing must be
replaced.
The cylinder bores should be checked with inside
micrometers or calipers. Cylinder bores which are scored
oroutof round by morethan.0005 in. ortaperedmore than
.0005in. should be re-bored orhoned oversize. Oversized
pistons and piston rings are available in .010 in., .020 in.
and .030 in. oversizes. Cylinder bores must be smooth,
straightandround.Clearancebetweenthecastironpistons
and cylinder bores should be between .002 in. minimum
and .004 in. maximum.
PISTON RINGS
Check the pistons for scores, cracks or enlarged ring
grooves; replace the pistons if any of these conditions are
found. Measure each piston with a micrometer in relation
to the cylinder bore diameter to be sure the diametrical
clearance is between .002 in. minimum and .004 in.
maximum.
Checkthe fit ofthe wrist pinsto the pistonsand connecting
rod bushings. The wrist pin should be a light press fit in
the piston. If the wrist pin is a loose fit, the piston and pin
assembly should be replaced. Check the fit of the wrist
pin in the connecting rod bushing by rocking the piston.
This clearance should not exceed .0007 in. Replace the
connecting rod and cap assembly which includes the wrist
pin bushings if excessive clearance is found. Check the fit
of the rings in the piston ring grooves. Check the ring gap
withtherings installed in thecylinderbores.Refer to Figure
12 for correct gap and groove clearances.
CRANKSHAFT
Check the crankshaft threads, keyways, tapered ends
and all machined and ground surfaces for wear, scores,
or damage. Standard crankshaft journals are 1.1242 in.
- 1.1250 in. in diameter. If the crankshaft journals are
excessively scored or worn or out of round and cannot be
reground, the compressor must be replaced. Connecting
rod bearing inserts are available in .010 in., .020 in.
and .030 in. undersizes for compressors with reground
crankshafts. Main bearing journals must be maintained
so the ball bearings are a snug fit or so that no more than
.005in.clearanceexistsbetweentheprecisionsleevemain
bearing and the main bearing journals on the crankshaft.
Check to be sure the oil passages are open through the
crankshaft.
CONNECTING ROD BEARINGS
Usedbearinginsertsmustbe replaced.Theconnectingrod
andcapare a matchedsetand therefore the capsmust not
be switched or rotated end for end. The solid inserts must
be installed in the rod and the slotted inserts into the cap.
Make sure the locating tangs on the inserts engage with
thelocatingnotchesintherodand cap. Clearance between
the connecting rod journal and the connecting rod bearing
must not be less than .0003 in. or more than .0021 in. after
rebuilding.
REPAIRS
UNLOADER
Anew cylinder headmaintenance kit shouldbe used when
rebuilding. Note: The entire contents of this kit must
be used. Failure to do so may result in compressor
failure. The unloader pistons in the kit are prelubricated
SIDE CLEARANCE
.000
.006
STANDARD PISTON
RING
.002
.004 OILRING
EXPANDER
RING
END GAP
.002
.013
.010
.040
Segment
Ring End
Gap
FIGURE 12 - RING CONFIGURATION
Compression

the slot toward the flange. Insert the crankshaft and the
rear thrust washer with the tang toward the rear of the
compressor.
Placetheoil seal ringonthe boss of therear end cover and
installthe end covermaking sure notto pinch theseal ring.
Ensure the tang of the thrust washer is inserted in the slot
of the end cover. Fasten the end cover to the crankcase
with the four cover cap screws. Torque the cap screws to
175-225 inch pounds in a cross pattern.
with a special lubricant piece number 239379 and need
no additional lubrication. Install the springs and unloader
pistons in their bores being careful not to cut the o-rings.
Install the unloader cover gasket and unloader cover and
secure the cover cap screws. Tighten the cap screws to
175-225 in. lbs. in a crossing pattern after first snugging
all screws.
DISCHARGE VALVES, VALVE STOPS AND
SEATS
If the discharge valve seats merely show signs of slight
wear, they can be dressed by using a lapping stone,
grinding compound and grinding tool, however, it is
recommended that a cylinder head maintenance kit be
used. Install new discharge valve springs and valves.
Screw in the discharge valve seats, and tighten to 70-90
ft.-lbs.Dischargevalve travel should bebetween.030 in. to
.046 in. To test for leakage by the discharge valves, apply
100 psi to the cylinder head discharge port and apply a
soap solution to the discharge valve and seats. Leakage
in the form of soap bubbles is permissible. If excessive
leakage is found, leave the air pressure applied and with
the use of a fiber or hardwood dowel and a hammer, tap
the discharge valves off their seats several times.This will
help the valves to seat and should reduce the leakage.
With the air pressure still applied at the discharge port of
the cylinder head, check for leakage around the discharge
valve stop on the top of the cylinder head casting. No
leakage is permitted.
INLET VALVES AND SEATS
Inlet valves and springs should be replaced. However, if
theinletvalve seats show signs ofslightnicks or scratches,
they can be redressed with a fine piece of emery cloth or
by lapping with a lapping stone, grinding compound and
grinding tool. If the seats are damaged to the extent that
they cannot be reclaimed, they must be replaced.
ASSEMBLY
General Note: All torques specified in this manual are
assembly torques and typically can be expected to fall off
after assembly is accomplished. Do not retorque after
initial assembly torques fall unless instructed otherwise.
Acompiled listing of torque specifications is presented on
page 13 of this manual.
To convert inch pounds of torque to foot pounds of torque,
divide inch pounds by 12.
inch pounds ÷ 12 = foot pounds
To convert foot pounds of torque to inch pounds of torque,
multiply foot pounds by 12.
foot pounds x 12 = inch pounds
INSTALLING CRANKSHAFT
Pressnewsleevebearingsintheendcoverandcrankcase.
Ensure that the slot in the bearings line up with the oil
passages in the end cover or crankcase. If you have a
model with no oil passage present in the crankcase, press
the sleeve bearing into the crankcase with the slot located
90 degrees from vertical.
Install the front thrust washer with the tang inserted in
FIGURE 13 - PISTON COMPARISON
2.78
2.17
1.06
1.25
OTHER BENDIX®
TU-FLO®AIR COMPRESSORS
TU-FLO®550
AIR COMPRESSOR
PISTON COMPARISON
FIGURE 14 - PISTON & RINGS
COMPRESSION RING (23)
SEGMENT RING (24)
SPACER RING (25)
SEGMENT RING
(24)

journal bearing segments (38) on the connecting rod (37)
and connecting rod cap (39). Tighten the connecting rod
bolts (40) evenly and torque to 150 - 170 inch pounds.
Install the other connecting rod and piston in the same
manner. It is recommended that new connecting rod cap
screws be used.
Before replacing the cylinder head on the crankcase
ensure the correct pistons have been used by turning the
crankshaft one complete revolution such that each piston
moves to its maximum upward stroke. At the maximum
upward stroke position each piston should move to the top
of the crankcase. If the piston does not approach the top
of the crankcase the piston is incorrect and if not replaced
could result in compressor damage.
BASE PLATE OR BASE ADAPTER
Position the base plate or base adapter gasket (20) on the
crankcase and install the base plate or base adapter (21)
asmarked before disassembly.Tightenthe six cap screws
(22),securingthe cast ironbaseadapter evenly toatorque
of175-225inchpoundsforbaseplateorcoverinacrossing
pattern after first snugging all 6 screws.
CYLINDER HEAD
Place the cylinder head gasket (19) and cylinder head
on the compressor crankcase and install the six cylinder
headcap screws. Snug the cylinderhead cap screws prior
to torquing the cap screws to 300-360 in. lbs. in a cross
pattern. Retorque the unloader cover cap screws to 170-
225 in. Ibs.
FINAL COMPRESSOR ASSEMBLY
Install all crankshaft keys making certain to support the
crankshaft to avoid bearing damage. Install the crankshaft
nut where applicable. When installing drive couplings or
gears, do not exceed 120 foot pounds torque on the
crankshaft nut.
Use covers, plugs, or masking tape to protect all ports if
compressor is not to be installed immediately. Protect the
ends of the crankshaft against damage by wrapping with
masking tape or friction tape.
TESTING REBUILT COMPRESSOR
In order to properly test a compressor under operating
conditions, a test rack for correct mounting, cooling,
lubricating,and driving thecompressor is necessary.Such
tests are not compulsory if the unit has been carefully
rebuilt by an experienced person.Acompressor efficiency
or build up test can be run which is not too difficult. An
engine lubricated compressor must be connected to an oil
supplyline of atleast 15 P.S.I.pressure during the test and
an oil return line must be installed to keep the crankcase
drained.
PISTONS AND CONNECTING RODS
If the pistons are to be replaced ensure that the correct
pistons are being installed. Note that the pistons for the
Tu-Flo®550 compressor are similar to those of otherBendix
compressor models but may be identified by the piston
diameterandthe distance to thecenterofthe wrist pin from
the top of the piston as shown in Figure 13.
PISTON RINGS
Check each ring end gap in a cylinder bore before
installation. Place the ring in the top of the cylinder bore
and using the piston, push the ring to the midpoint of the
cylinder bore and check the ring gap. If the end gaps are
incorrect either the wrong repair size has been purchased
orthecompressor is wornbeyondspecification and should
be replaced.
Installtherings on thepistonsper the followinginstructions
starting at the center of the piston and moving outward.
1. Install the spacer and segment rings as follows. Place
the spacer ring (25) in the piston groove, the ends of
the spacer must butt and not overlap. Install the top
segment (24) by inserting one end above the spacer
in the ring groove, 120 degrees from the spacer ends
and wind the segment into position. Install the bottom
segment in the same manner beneath the spacer
making sure the gap is staggered 120 degrees from
both the top ring segment and the spacer end gaps.
Before using be sure both painted ends of the spacer
are visible and butted.
2. Installthecompression rings (23)inthe proper grooves
with the bevel or “pip” mark (if any) toward the top of
the piston. (Refer to Figure 14.)
Checkthering side clearance ofeachring in thepistonring
groove. (Refer to Figure 14.) If the side clearance is too
large, the piston ring groove is worn beyond specifications
and the piston must be replaced.
Rotate the piston rings in their respective groove so that
each end gap is at least 90 degrees from the previous
ring’s end gap.
Lubricate the wrist pin (22) and wrist pin bushing in the
connectingrod with engineoil.Assemble theupper portion
of the connecting rods and the pistons with the wrist pins.
Insert the wrist pin buttons (28) in the ends of the wrist pin.
Lubricatethe pistons and ringswith engine oil.Usinga ring
compression tool return the piston to the cylinder bore.
Turn thecrankshaftsothatone ofitsconnectingrodjournals
is in the downward, center position. Install the crankshaft

Connectto the compressor dischargeport, a reservoirwith
avolume of 1500 cubic inches,including the volume of the
connecting line. With the compressor operating at 2100
R.P.M., the time required to raise the reservoir(s) pressure
from85psi to 100 psishouldnot exceed 7 seconds.During
this test, the compressor should be checked for gasket
leakageandnoisy operation, as wellasunloader operation
and leakage.
If the compressor functions as indicated reinstall on the
vehicle connecting all lines as marked in the disassembly
procedure.
TU-FLO®550 AIR COMPRESSOR
SPECIFICATIONS
Average weight ........................................................... 53
Number of cylinders ...................................................... 2
Bore size ............................................................. 2.78 In.
Stroke ................................................................. 1.50 In.
Displacement at 1250 RPM ............................ 13.2 CFM
Maximum recommended RPM ...................... 3000 RPM
Minimum coolant flow (water cooled) at
Maximum RPM .............................................. 2.5 GPM
Minimum RPM ................................................. .5 GPM
Approximate horsepower required at
1250 RPM at 120 PSIG (naturally aspirated) ............ 2.5
Turbocharge limits
See Compressor Turbocharging Parameters
Maximum inlet air temperature .............................. 250°F
Maximum discharge air temperature ..................... 400°F
Minimum pressure required to unload
(naturally aspirated) ........................................... 60 PSIG
Minimum oil pressure required at
engine idling speed ............................................ 15 PSIG
Minimum oil pressure required at
maximum governed engine speed .................... 15 PSIG
Minimum discharge-line size ............................. 1/2" I.D.
Minimum coolant-line size ................................. 3/8" I.D.
Minimum oil-supply line size ............................ 3/16" I.D.
Minimum oil-return line size ............................... 1/2" I.D.
Minimum air-inlet line size .................................. 5/8” I.D.
Minimum unloader-line size ............................. 3/16" I.D.
TORQUE SPECIFICATIONS
Bolt, Nut or Screw ........................... Assembly Torque
(in. lbs.)
Cylinder Head ..................................................440 - 500
Unloader Cover Plate ...................................... 175 - 225
Discharge Valve Seat ............. 840 - 1080 (70-90 ft. lbs.)
Inlet Valve Stop ....................... 840 - 1080 (70-90 ft. lbs.)
End Cover ........................................................ 175 - 225
Connecting Rod ............................................... 150 - 170
Bottom Cover ................................................... 175 - 225
Air Strainer ....................................................... 125 - 150
Inlet Fitting ....................................................... 175 - 225
Discharge Fitting .............................................. 175 - 225
Governor or Governor Adapter ........................ 175 - 225
Pipe Plugs
1/16 .................................................................. 35 - 50
1/8 .................................................................. 85 - 105
1/4 ................................................................ 130 - 170
3/8 ................................................................ 160 - 200
1/2 ................................................................ 200 - 270
Pipe Bushing
1/2 ................................................................ 175 - 225
Crankshaft Nut:
Marsden or Castle ........... 1200-1440 (100-120 ft. lbs.)
P/N 298125 (Metric Thread)......2640-3048 (220-254 ft.
lbs.)
DIMENSIONAL DATA
Port Sizes
Water inlet ............................................... 1/2 - 14 NPT
Water outlet ............................................. 1/2 - 14 NPT
Air discharge ........................................... 1/2 - 14 NPT
Governor ................................................. 1/8 - 27 NPT
Oil inlet (end cover) ................................. 1/8 - 27 NPT
Oil return: Base mount ........................... 1/2 - 14 NPT
Piston
(standard) .................................................. 2.77825 in.
(.010 oversize) .......................................... 2.78825 in.
(.020 oversize) .......................................... 2.79825 in.
(.030 oversize) .......................................... 2.80825 in.
Cylinder bore
(standard) .................................................... 2.7810 in.
(.010 oversize) ............................................ 2.7910 in.
(.020 oversize) ............................................ 2.8010 in.
(.030 oversize) ............................................. 2.8110 in.
MAINTENANCE KITS AND AVAILABLE SERVICE
PARTS
Cylinder Maintenance Kit
Piston Ring Kit (standard and oversizes)
Piston and Rod Kit (standard and oversizes)
Crankshaft Bearing Kit
Gasket & Seal Kit

COMPRESSOR TROUBLESHOOTING
IMPORTANT:The troubleshooting contained in thissection
considers the compressor as an integrated component of
the overall air brake charging system and assumes that
an air dryer is in use. The troubleshooting presented will
covernotonlythecompressoritself,butalsoothercharging
system devices as they relate to the compressor.
WARNING! PLEASE READ AND FOLLOW
THESEINSTRUCTIONSTOAVOIDPERSONAL
INJURY OR DEATH:
When working on or around a vehicle, the following
general precautions should be observed at all times.
1. Parkthevehicleonalevelsurface,applytheparking
brakes,andalways blockthewheels. Alwayswear
safety glasses.
2. Stop the engine and remove ignition key when
workingunderoraroundthevehicle. Whenworking
in the engine compartment, the engine should be
shut off and the ignition key should be removed.
Where circumstances require that the engine be
in operation, EXTREME CAUTION should be used
to prevent personal injury resulting from contact
withmoving,rotating,leaking,heatedorelectrically
charged components.
3. Do not attempt to install, remove, disassemble
or assemble a component until you have read
and thoroughly understand the recommended
procedures. Useonlythepropertoolsandobserve
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®airdryersystemoradryerreservoirmodule,
be sure to drain the purge reservoir.
5. Followingthevehiclemanufacturer’srecommended
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
bedesignedspecificallyforsuch applications and
systems.
9. Components with stripped threads or damaged
parts should be replaced rather than repaired. Do
notattemptrepairsrequiringmachiningorwelding
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),
the ATC function must be disabled (ATC indicator
lampshouldbeON)priortoperforminganyvehicle
maintenance where one or more wheels on a drive
axle are lifted off the ground and moving.

16

A-1
Appendix A
Advanced Troubleshooting Guide for Air Brake Compressors
Air brake charging system:
Slow build (9.0).....................................A-9-10
Doesn’t build air (10.0).............................A-11
Air dryer:
Doesn’t purge (14.0)................................A-12
Safety valve releases air (12.0)...............A-12
Compressor:
Constantly cycles (15.0) ..........................A-12
Leaks air (16.0)........................................A-13
Safety valve releases air (11.0) ............... A-11
Noisy (18.0) ............................................A-13
Reservoir:
Safety valve releases air (13.0)...............A-12
INDEX
Air Coolant
Engine
Oil
Compressor leaks coolant (17.0)....................A-13
Oil consumption (6.0) ......................................A-9
Oil Test Card results (1.0).................................A-4
Oil is present:
On the outside of the compressor (2.0)......A-5
At the air dryer purge/exhaust
or surrounding area (3.0)........................A-5
In the supply reservoir (4.0).................... A-6-8
At the valves (5.0).......................................A-8
At air dryer cartridge (7.0)...........................A-9
In the ping tank or compressor
discharge aftercooler (8.0)......................A-9
Symptom Page Number
(1) Oil Leakage at Head Gasket .....A-14
(2) System Leakage .......................A-14
(3) Compressor Discharge and
Air Dryer Inlet Temperature...........A-15
(4) Governor Malfunction ................A-14
(5) Governor Control Line ...............A-15
(6) Compressor Unloader ...............A-15
BASIC™Test Information........ A-16-18
Test Procedures
Maintenance Schedule and
Usage Guidelines (Table A)..... A-3
Symptom Page Number
Maintenance & Usage Guidelines
Theguide consists of anintroduction to airbrake charging systemcomponents, a table
showingrecommendedvehiclemaintenanceschedules,andatroubleshootingsymptom
and remedy section with tests to diagnose most charging system problems.

A-2
Introduction to the Air Brake Charging System
Powered by the vehicle engine, the air compressor
builds the air pressure for the air brake system. The air
compressoristypicallycooledbythe engine coolant system
and lubricated by the engine oil supply.
The compressor's unloader mechanism and governor
(along with a synchro valve for the Bendix®DuraFlo™596
air compressor) control the brake system air pressure
between a preset maximum and minimum pressure level
by monitoring the pressure in the service (or “supply”)
reservoir. Whentheairpressurebecomesgreaterthanthat
of the preset “cut-out”, the governor controls the unloader
mechanismofthe compressor to stop thecompressorfrom
building air and also causes the air dryer to purge. As the
service reservoir air pressure drops to the “cut-in” setting
ofthe governor,the governor returnsthe compressor back
to building air and the air dryer to air drying mode.
As the atmospheric air is compressed, all the water vapor
originally in the air is carried along into the air system, as
well as a small amount of the lubricating oil as vapor.
The duty cycle is the ratio of time the compressor spends
buildingair tothetotalenginerunning time. Aircompressors
are designed to build air (run “loaded”) up to 25% of the
time. Higher duty cycles cause conditions that affect air
brake charging system performance which may require
additionalmaintenance. Factors that add to theduty cycle
are: air suspension, additional air accessories, use of an
undersizedcompressor,frequent stops, excessive leakage
from fittings, connections, lines, chambers or valves, etc.
The discharge line allows the air, water-vapor and
oil-vapor mixture to cool between the compressor and air
dryer. The typical size of a vehicle's discharge line, (see
column 2 of Table A on page A-3) assumes a compressor
with a normal (less than 25%) duty cycle, operating in
a temperate climate. See Bendix and/or other air dryer
manufacturer guidelines as needed.
When the temperature of the compressed air that enters
the air dryer is within the normal range, the air dryer can
removemost of the chargingsystem oil. If the temperature
of the compressed air is above the normal range, oil as
oil-vapor is able to pass through the air dryer and into the
air system. Larger diameter discharge lines and/or longer
discharge line lengths can help reduce the temperature.
The discharge line must maintain a constant slope down
fromthecompressor to theairdryer inlet fittingtoavoid low
points where ice may form and block the flow. If, instead,
ice blockages occur at the air dryer inlet, insulation may
be added here, or if the inlet fitting is a typical 90 degree
fitting, it may be changed to a straight or 45 degree fitting.
For more information on how to help prevent discharge
line freeze-ups, see Bendix Bulletins TCH-08-21 and
TCH-08-22 (see pages A-19-21). Shorter discharge line
lengths or insulation may be required in cold climates.
Theair dryer contains a filter that collectsoil droplets, and
a desiccant bed that removes almost all of the remaining
water vapor. The compressed air is then passed to the air
brake service (supply) reservoir. The oil droplets and the
watercollectedareautomatically purged when the governor
reaches its “cut-out” setting.
For vehicles with accessories that are sensitive to small
amounts of oil, we recommended installation of a Bendix®
PuraGuard®systemfilter,designedto minimize the amount
of oil present.
Air Dryer
Reservoir Drain
Service Reservoir
(Supply Reservoir)
Compressor
Governor
(Governor plus Synchro valve
for the Bendix®DuraFlo™596
Compressor)
Discharge
Line Optional “Ping” Tank
Optional Bendix®PuraGuard®
System Filter or PuraGuardQC™
Oil Coalescing Filter
The Air Brake Charging System supplies the
compressedairfor the braking systemaswell as other air
accessories for the vehicle. The system usually consists
of an air compressor, governor, discharge line, air dryer,
and service reservoir.

A-3
Compressor with up to 25% duty cycle
Footnotes:
1. With increased air demand the air dryer cartridge needs to be
replaced more often.
2. Use the drain valves to slowly drain all reservoirs to zero psi.
3. Allow the oil/water mixture to fully settle before measuring oil
quantity.
4. To counter above normal temperatures at the air dryer inlet, (and
resultant oil-vapor passing upstream in the air system) replace the
discharge line with one of a larger diameter and/or longer length.
Thishelps reduce the air's temperature. Ifsufficientcooling occurs,
the oil-vapor condenses and can be removed by the air dryer.
Discharge line upgrades are not covered under warranty. Note:
To help prevent discharge line freeze-ups, shorter discharge line
lengths or insulation may be required in cold climates. (See Bendix
Recom- Recom- Acceptable
Typical Discharge mended mended Reservoir
Compressors Line Air Dryer Reservoir Oil Contents3
No. of Spec'd Cartridge Drain at Regular
Axles Replacement1Schedule2Drain Interval
High Air Use
Low Air Use
e.g. Double/triple trailer, open
highway coach/RV, (most)
pick-up & delivery, yard or
terminal jockey, off-highway,
construction, loggers, concrete
mixer, dump truck, fire truck.
e.g. Line haul single trailer
w/o air suspension, air over
hydraulic brakes.
e.g. Line haul single trailer
with air suspension,
school bus.
5
or
less
5
or
less
8
or
less
12
or
less
Table A: Maintenance Schedule and Usage Guidelines
Recom-
mended
Every
Month -
Max of ev-
ery 90 days
Every
Month
Every 3
Years
Every 2
Years
Every
Year
I.D.
Vehicle Used for:
Column 1 Column 2 Column 3 Column 4 Column 5
Regularly scheduled maintenance is the single most important factor in maintaining the air brake charging
Length
6 ft.
1/2 in.
9 ft.1/2 in.
12 ft.
1/2 in.
3/4 in. 12 ft.
BASIC™test
acceptable
range:
5 oil units
per month.
See
appendix
A.
For oil carry-over
control4 suggested
upgrades:
5/8 in. 15 ft.
For oil carry-over
control4 suggested
upgrades:
5/8 in. 9 ft.
For oil carry-over
control4 suggested
upgrades:
5/8 in. 12 ft.
Compressor with less than 15% duty
cycle
Compressor with up to 25% duty cycle
Compressor with up to 25% duty cycle
Bendix®BA-921®air compressor
Bendix®Tu-Flo®550 air compressor
Bendix®Tu-Flo®750 air compressor
Bendix®BA-922®, or DuraFlo™596 air compressor
BASIC™test
acceptable
range:
3 oil units
per month.
See
appendix
A.
For the
BASIC™
Test Kit:
Order
Bendix
P/N
5013711
e.g. City transit bus, refuse,
bulk unloaders, low boys,
urban region coach, central
tire inflation.
(See footnote 7)
Bulletins TCH-08-21 and TCH-08-22, included in Appendix B, for
more information.)
5. For certain vehicles/applications, where turbo-charged inlet air is
used, a smaller size compressor may be permissible.
6. Note: Compressor and/or air dryer upgrades are recommended
in cases where duty cycle is greater than the normal range (for
the examples above).
7. For correct compressor upgrades consult Bendix - Please note
that because a compressor is listed in the same area of the chart
does not necessarily mean that it would be a suitable candidate
for upgrade purposes.
For Bendix®Tu-Flo®550 and 750 compressors, unloader service is
recommended every 250,000 miles.

A-4
Air Brake Charging System Troubleshooting
1.0 Oil Test Card
Results Not a valid test. Discontinue using this test.
Donotusethiscardtesttodiagnosecompressor
"oil passing" issues. They are subjective
and error prone. Use only the Bendix®Air
System Inspection Cup (BASIC™) test and the
methods described in this guide for advanced
troubleshooting.
The Bendix®BASIC™test should be the
definitive method for judging excessive
oil fouling/oil passing. (See Appendix A,
on page A-16 for a flowchart and expanded
explanation of the checklist used when
conducting the BASIC™test.)
Symptom: What it may indicate: What you should do:
How to use this guide:
Find the symptom(s) that you see, then move to the right
to find the possible causes (“What it may indicate”) and
remedies (“What you should do”).
Review the warranty policy before performing any intrusive
compressor maintenance. Unloader or cylinder head gasket
replacement and resealing of the bottom cover plate are
usually permitted under warranty. Follow all standard safety
procedures when performing any maintenance.
Look for:
Normal - Charging system is working within
normal range.
Check - Charging system needs further
investigation.
Bendix®
BASIC™ Test
WARNING! Please READ and follow these instructions to
avoid personal injury or 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,theengine should be shut offand the ignition
keyshouldbe removed. Where circumstances requirethat
theenginebeinoperation,EXTREMECAUTIONshould 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
assemblea component until youhave read andthoroughly
understand the recommended procedures. Use only 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, 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. Useonlygenuine 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 certain all
components and systems are restored to their proper
operating condition.
11. For vehicles withAntilock Traction Control (ATC), theATC
function must be disabled (ATC indicator lamp should be
ON) prior to performing any vehicle maintenance where
oneor more wheelsona drive axleare lifted off the ground
and moving.
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