Bendix BA-921 Service Manual

BENDIX® BA-921® COMPRESSOR

DESCRIPTION

The function of the air compressor is to provide and maintain air under pressure to operate devices in air brake systems. The Bendix® BA-921® compressor is a single-cylinder reciprocating compressor with a rated displacement of 15.8 cubic feet per minute at 1250 RPM.

The compressor consists of a water-cooled cylinder head assembly and an integral air-cooled crankcase assembly.

The cylinder head assembly is made up of the cylinder head, cooling plate and valve plate assembly and uses two sealing gaskets. Depending on the application, the cylinder head and cooling plate may be aluminum or cast iron. The cylinder head contains air and water ports as well as an unloader assembly. A cooling plate is located between the cylinder head and valve plate assemblies and assists in cooling.

The valve plate assembly consists of brazed steel plates which have valve openings and passages for air and engine coolant to ﬂow into and out of the cylinder head. The compressor's discharge valves are part of the valve plate assembly. The inlet reed valve/gasket is installed between the valve plate assembly and the top of the crankcase.

Splash	Coolant Ports
Shield	(3 total)
Unloader
Cover
Unloader	Air
Piston	Intake
Discharge	Cooling
Reed	Plate
Valves (2)
Piston	Crankshaft
Piston

Piston

Rod

Crankcase

Cover

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Cylinder	Safety
Cylinder	Valve
Head

Valve Plate

Assembly

Cooling

Plate

Crankcase

FIGURE 2 - BENDIX® BA-921® COMPRESSOR

The cast iron crankcase houses the piston assembly, connecting rod, crankshaft and related bearings.

All Bendix® BA-921® compressors are equipped with a safety valve to protect the compressor head in the event of, for example, a discharge line blockage downstream of the compressor. Excessive air pressure will cause the safety valve to unseat, release air pressure and give an audible alert to the operator. The safety valve is installed in the cylinder head safety valve port, directly connected to the cylinder head discharge port.

The crankcase cover located at the bottom of the crankcase is stamped with information identifying the compressor model, customer piece number, Bendix piece number and serial number. See Figures 2 and 3.

Compressor Model,

Customer Piece Number,

Bendix Piece Number and

Serial Number shown here

FIGURE 1 - BENDIX® BA-921® COMPRESSOR (CUT-AWAY)

FIGURE 3 - CRANKCASE BASE COVER

Caterpillar	Caterpillar	Detroit
C7, C9	HD Acert	Diesel S60
Engines	Engines

FIGURE 4 - TYPICAL COMPRESSOR DRIVE FLANGES	piston to move upwards, away from its seat on the valve
	plate assembly. When the unloader piston is unseated an

OPERATION

The compressor is driven by the vehicle's engine and functions continuously while the engine is in operation. Actual compression of air is controlled by the compressor unloading mechanism operating in conjunction with a governor.

AIR INTAKE (LOADED)

Just as the piston begins the down stroke, (a position known as top dead center, or TDC), the vacuum created in the cylinder bore above the piston causes the inlet reed valve to ﬂex open. Atmospheric air (in naturally aspirated applications) or pressurized air (in turbocharged applications) ﬂows through the open inlet valve and ﬁlls the cylinder bore above the piston. See Figure 5.

AIR COMPRESSION (LOADED)

When the piston reaches the bottom of the stroke, (a position known as bottom dead center, or BDC), the inlet reed valve closes. Air above the piston is trapped by the closed inlet reed valve and is compressed as the piston moves upwards. When air in the cylinder bore reaches a pressure greater than that of the system pressure, the discharge reed valves open and allow air to ﬂow into the discharge line and air brake system.

At the same time air ﬂows into the hollow center of the unloader piston through an opening in the end of the piston. Compressed air acts on the interior surfaces of the unloader piston and, along with the unloader piston spring, holds the unloader piston in the down position, against its seat on the valve plate. See Figure 7.

NON-COMPRESSION OF AIR (UNLOADED)

When air pressure in the supply reservoir reaches the cutout setting of the governor, the governor delivers system air to the compressor unloader port. Air entering the unloader port acts on the unloader piston causing the

Air	Air Inlet	Discharge
Air	Port	Valve	Unloader
Discharge		Closed	Unloader
Discharge			Port
Port			Port
Port
Cooling
Plate
Valve
Plate			Unloader
			Piston
			Down &
			Seated
			Inlet
			Valve
			Open
	Piston Moving Down

FIGURE 5 - OPERATION - LOADED (INTAKE)

An Inlet Check Valve (ICV),
or alternately, an ICV plus a reservoir,
is used in the air inlet line depending on
the application
Governor	Air Dryer
Unloader Port
Governor
Reservoir
Port
Compressor
	Supply Reservoir

FIGURE 6 - BA-921® COMPRESSOR UNLOADER SYSTEM

	Air Inlet	Discharge
Air	Port	Valve	Unloader
Air		Open	Port
Discharge
Port

Cooling
Plate
Valve
Plate
Inlet	Unloader
Valve	Piston
Closed	Down &
	Seated

Piston Moving Up

FIGURE 7 - OPERATION - LOADED (COMPRESSION)

air passageway is opened between the cylinder bore and the air inlet cavity in the cylinder head.

As the piston moves from bottom dead center (BDC) to top dead center (TDC) air in the cylinder bore ﬂows past the unseated unloader piston, into the cylinder head inlet cavity and out the inlet port. To prevent the air from ﬂowing back into the engine air induction system, an inlet check valve (ICV) is installed upstream of the air compressor inlet port. The location of the device and the way it is plumbed into the compressor air induction system is unique to the speciﬁc engine and the type of air induction (naturally aspirated or boosted air) the compressor uses. These air induction systems will be explained in further detail in the “Air Induction” section on page 4. On the piston down stroke (TDC to BDC) air ﬂows in the reverse direction, from the inlet cavity past the unseated unloader piston and inlet reed valve, and into the cylinder bore.

LUBRICATION

The vehicle's engine provides a continuous supply of oil to the compressor. Oil is routed from the engine to the compressor's oil inlet. An oil passage in the crankshaft routes pressurized oil to the precision sleeve main bearings and to the connecting rod bearings. Spray lubrication of the cylinder bores, connecting rod wrist pin bushings, and ball type main bearings is obtained as oil is forced out around the crankshaft journals by engine oil pressure. Oil then falls to the bottom of the compressor crankcase and is returned to the engine through drain holes in the compressor mounting ﬂange.

Lubrication for Caterpillar C11 and C13 engine applications

Bendix® BA-921® compressor - for Caterpillar C11 and C13 engine installations only - use an "oil jet" that sprays oil under the piston for purposes of cooling. This oil jet is part of a special crankcase cover that is used only on the BA-921® compressor for CAT C11 and C13 engine installations (see Figure 14).

This design slightly alters the ﬂow of oil for lubrication. The oil supply line from the engine is directly connected to the back side of the special crankcase over. The oil ﬂows in parallel through a passageway in the crankcase cover and through the oil jet to spray oil under pressure up onto the underneath of the piston for cooling. At the same time, oil ﬂows out of the opposite end of the special crankcase cover, through a ﬁtting and a metal tube and second ﬁtting into the oil supply port of the compressor. At this point oil ﬂows in a similar manner as in the ﬁrst paragraph of this section.

COOLING

Bendix® BA-921® compressors are cooled by air ﬂowing through the engine compartment as it passes the compressor's cast-in cooling ﬁns and by the ﬂow of engine coolant through the cylinder head. Coolant supplied by the engine cooling system passes through connecting lines into the cylinder head and passes through internal passages in the cylinder head, cooling plate and valve plate assembly and returns to the engine. Figure 9 illustrates the various approved coolant ﬂow connections. Proper cooling is important in minimizing discharge air temperatures - see the tabulated technical data on page 14 of this manual for speciﬁc requirements.

Air Inlet Port	Air From
Air Inlet Port	Governor
	Unloader
	Port
Cooling
Plate
Valve	Unloader
Plate	Piston Up &
	Unseated

Air in Pistons Shuttles Back and Forth from the Piston to the Cylinder Head and Inlet Port During Unloaded Mode

FIGURE 8 - OPERATION - UNLOADED

AIR INDUCTION GENERAL

The Bendix® BA-921® air compressor can be used both with air induction systems that are naturally aspirated (atmospheric air) and pressurized (turbocharged). The following section covers Caterpillar and Detroit Diesel engine air induction arrangements. See Figure 4, for typical ﬂanges used.

CATERPILLAR

Caterpillar HD ACERT engines (C11, C13, C15 and C18) and MD ACERT engines (C7 and C9) are typically equipped with Bendix® BA-921® compressors. These engines provide pressurized (turbocharged) air to the compressor's inlet port. Caterpillar recommends the use of an inlet check valve in the air induction system to prevent the air from the compressor being forced back into the engine air induction system when the compressor is operating in the "unloaded" condition (not building air). Because the compressor induction system is turbocharged, an additional air volume (reservoir) is required between the compressor inlet port and the inlet check valve to prevent excessive air pressure at the compressor inlet in the unloaded mode. Figures 10 and 11 show example of the different air induction systems used by Caterpillar to perform this function.

CATERPILLAR C7/C9 ENGINES

The Bendix® BA-921® compressor in the C7/C9 air induction system (see Figure 10) receives its air from the engine's intake manifold (turbocharged). During the pumping condition (loaded mode), the air ﬂows from the engine intake manifold through the inlet check valve and inlet line to the compressor inlet port. During the non-pumping condition (unloaded mode), the compressor cylinder pushes air back out of the inlet port to the inlet check valve. The ICV prevents the air from traveling beyond this point. Because the air is boosted (under pressure), it is important that the compressor inlet line is of sufﬁcient length, strength and volume to minimize the build-up of air pressure in the inlet system. The air shuttles back and forth between the compressor cylinder bore and the ICV during this phase of the compressor operation.

CATERPILLAR C11, C13, C15 AND C18 ENGINES

The Bendix® BA-921® compressor in the C11, C13, C15, and C18 air induction systems (see Figure 11) receives its air from the engine's intake manifold (turbocharged). During the pumping condition (loaded mode), the air ﬂows from the engine intake manifold through the inlet check valve, expansion tank and inlet line to the compressor inlet port. During the non-pumping condition (unloaded mode), the compressor cylinder pushes air back out of the inlet port into the expansion tank. The ICV (at the end of the

Head	Discharge	Coolant In or Out
Bolt (4)	Discharge	Coolant In or Out
Bolt (4)	Safety Valve	(One or other not used)
	Safety Valve	(One or other not used)
Discharge
Port

Governor

Connection

Inlet

Unloader Port

Cover

Coolant In or Out

CYLINDER HEAD PORT IDENTIFICATION

The cylinder head connection ports are identiﬁed with cast in numerals as follows:

AIR IN	0
Compressed AIR OUT	2
Coolant IN or OUT	9
Governor Control	4

FIGURE 9 - TYPICAL BENDIX® BA-921® COMPRESSOR

CYLINDER HEAD

expansion tank) prevents the air from traveling beyond this point. Because the air is boosted (under pressure), it is important that the compressor inlet line is of sufﬁcient length, strength and volume to minimize the build-up of air pressure in the inlet system. The air shuttles back and forth between the compressor cylinder bore and the expansion tank during this phase of the compressor operation.

Inlet

Port

Inlet

Line

		Air Supply
Inlet Check Valve	F	rom Engin	e

FIGURE 10 - EXAMPLE OF CATERPILLAR (ACERT

ENGINE) C7/C9 COMPRESSOR AIR INDUCTION SYSTEM (TURBOCHARGED)

Inlet

Line

Expansion Tank

Inlet

Port

Air Supply

From Engine

Inlet Check Valve

FIGURE 11 - EXAMPLE CATERPILLAR (HD ACERT

ENGINE) C11/C13/C15/C18 COMPRESSOR AIR INDUCTION SYSTEM (TURBOCHARGED)

DETROIT DIESEL

The Detroit Diesel Series 60 (EGR) engine is equipped with the Bendix® BA-921® compressor and uses naturally aspirated air induction system. Detroit Diesel recommends the use of an inlet check valve in the air induction system to prevent the air from the compressor cylinder bore from being forced back into the engine air induction system when the compressor is in the unloaded mode (non-pumping condition). A flexible high-pressure hose is installed between the inlet check valve and the compressor inlet ﬁtting. This hose can be of various lengths to accommodate the distance between the compressor and inlet check valve. See Figure 12.

Fr

Inlet	Inlet
Inlet		Port
Check		Port


Valve

FIGURE 12 - EXAMPLE OF DETROIT DIESEL (EGR) S60

COMPRESSOR AIR INDUCTION SYSTEM (NATURALLY ASPIRATED)

During operation, non-pressurized air from the engine's air source is routed to the compressor from a point between the engine air ﬁlter and the non-pressure side of the turbocharger. When the compressor is building air (loaded mode), the air ﬂows from the engine intake tube, through the inlet check valve into the inlet port of the compressor. When the compressor is not building air (unloaded mode), the compressor pushes the air back out the compressor during the cylinder upstroke towards the inlet check valve. The ICV prevents the air from traveling beyond this point. The air shuttles back and forth between the compressor cylinder bore and the ICV during this phase of the compressor operation.

PREVENTATIVE 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 on page 17, for a guide to various considerations that must be given to maintenance of the compressor and other related charging system components.

Important Note: Review the warranty policy before performing any intrusive maintenance procedures. An extended warranty may be voided if intrusive maintenance is performed during this period.

EVERY 6 MONTHS, 1800 OPERATING HOURS OR AFTER EACH 50,000, MILES WHICHEVER OCCURS FIRST, PERFORM THE FOLLOWING INSPECTIONS AND TESTS.

AIR INDUCTION

The Bendix® BA-921® compressor is designed for connection to the vacuum side of the engine’s air induction system and the pressure side (turbocharged) of the engine’s air induction system.

A supply of clean air is one of the single most important factors in compressor preventive maintenance. Since the air supply for BA-921® compressor and engine is the engine air cleaner, periodic maintenance of the engine air ﬁlter is necessary.

Inspect the compressor air induction system each time engine air cleaner maintenance is performed.

1.Inspect the intake hose adapters for physical damage. Make certain to check the adapters at both ends of the intake hose or tubing.

2.Inspect the intake hose clamps and tighten them if needed.

3.Inspect the intake hose or line for signs of drying, cracking, chaﬁng and ruptures and replace if necessary.

4.Verify that the compressor inlet ﬁtting is tight (check torque).

5.Any metal tubes should also be tight (torqued properly) to the mating ﬁtting. Inspect the metal tubes for any cracks or breaks and replace if necessary.

6.If an expansion tank is present (turbocharged air induction systems only), inspect any cracks and replace if necessary.

COMPRESSOR COOLING

Inspect the compressor discharge port, inlet cavity and discharge line for evidence of restrictions and carbon buildup. If more than 1/16" of carbon is found, thoroughly clean or replace the affected parts. In some case, carbon buildup indicates inadequate cooling. Closely inspect the compressor cooling system. Check all compressor coolant lines for kinks and restrictions to ﬂow. Minimum coolant line size is 3/8" I.D. Check coolant 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

Check the external oil supply line for kinks, bends, or restrictions to ﬂow. Supply lines must be a minimum of 3/16” I.D. 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 oil seepage and refer to the TROUBLESHOOTING section for appropriate tests and corrective action.

Note: This is applicable only for Caterpillar engine installations. Detroit Diesel utilizes an internal oil feed design. No external oil supply line is used.

OIL PASSING

All reciprocating compressors pass a minimal amount of oil. Air dyers will remove the majority of oil before it can enter the air brake system. For particularly oil sensitive systems, the Bendix® PuraGuard® system can be use 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™ kit to help substantiate suspected excessive oil passing. The steps to be followed when using the BASIC™ kit are presented in APPENDIX A at the end of the TROUBLESHOOTING section.

COMPRESSOR DRIVE

Check for noisy compressor operation, which could indicate excessive drive component wear. Adjust and/or replace as necessary. Check all compressor mounting bolts and retighten evenly if necessary. Check for leakage and proper unloader mechanism operation. Repair or replace parts as necessary.

COMPRESSOR UNLOADER & GOVERNOR

Test and inspect the compressor and governor unloader system for proper operation and pressure setting.

1.Check for leakage at the unloader port. Replace leaking or worn o-rings.

2.Make certain the unloader system lines are connected as illustrated in Figure 6.

3.Cycle the compressor through the loaded and unloaded cycle several times. Make certain that the governor cuts-in (compressor resumes compressing air) at a minimum of 105psi (cut-out should be approximately 15 - 20psi greater than cut-in pressure). Adjust or replace the governor as required.

4.Note that the compressor cycles to the loaded and unloaded conditions promptly. If prompt action is not noted, repair or replace the governor and/or repair the compressor unloader.

IMPORTANT NOTE

Replacement air governors must have a minimum cut-in pressure of 100psi. The cut-in pressure is the lowest system pressure registered in the gauges before the compressor resumes compressing air.

Compressors with no signal line to the unloader port should have a vent cap (e.g. Bendix part number 222797) installed in the port. Under no circumstances should the port be plugged or left open.

SERVICE TESTS

GENERAL

The following compressor operating and leakage tests need not be performed on a regular basis. These tests should be performed when it is suspected that leakage is substantially affecting compressor buildup performance, or when it is suspected that the compressor is “cycling” between the loaded (pumping) and unloaded (non-pumping) modes due to unloader leakage.

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 retest 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 15 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 engine running at high idle (instead of maximum 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 throughout the vehicle’s service life can 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 15 of this document, to assist investigation of the cause(s).

Note: When comparing build-up times, be sure to make an allowance for any air system modiﬁcations which would cause longer times, such as adding air components or reservoirs. Always check for air system leakage.

LEAKAGE TESTS

See the standard Air Brake System and Accessory Leakage test on Page 28 (Test 2).

Note: Leakage in the air supply system (components before the supply reservoir - such as the governor, air dryer, reservoir drain cocks, safety valve and check valves) will not be registered on the vehicle dash gauges and must be tested separately. Refer to the various maintenance manuals for individual component leakage tests and the Bendix “Test and Checklist” published in the Air Brake System Handbook (BW5057) and on the back of the Dual Circuit Brake System Troubleshooting Card (BW1396).

CYLINDER HEAD

Check for cylinder head gasket air leakage.

1.With the engine running, lower air system pressure to 60 psi and apply a soap solution around the cylinder head. Check the gasket between the cylinder head and valve plate assembly and the inlet reed valve/gasket between the valve plate assembly and crankcase for air leakage.

2.No leakage is permitted. If leakage is detected replace the compressor or repair the cylinder head using a genuine Bendix maintenance kit available from an authorized Bendix parts outlet.

INLET, DISCHARGE & UNLOADER

In order to test the inlet and discharge valves and the unloader piston, it is necessary to have shop air pressure and an assortment of ﬁttings. A soap solution is also required.

1.With the engine shut off, drain ALL air pressure from the vehicle.

2.Disconnect the inlet and discharge lines and remove the governor or its line or adapter ﬁtting.

3.Apply 120-130 psi shop air pressure to the unloader port and soap the inlet port. Leakage at the inlet port should not exceed 50 sccm.

4.Apply 120-130 psi shop air pressure to the discharge port and then apply and release air pressure to the inlet port. Soap the inlet port and note that leakage at the inlet port does not exceed 20 sccm.

If excessive leakage is noted in Tests 3 or 4, replace or repair the compressor using genuine Bendix replacements or maintenance kits available from any authorized Bendix parts outlet.

While it is possible to test for inlet, discharge, and unloader piston leakage, it may not be practical to do so. Inlet and discharge valve leakage can generally be detected by longer compressor build-up and recovery times. Compare current compressor build-up times with the last several recorded times. Make certain to test for air system leakage, as described under In Service Operating Tests, before making a determination that performance has been lost.

Unloader leakage is generally exhibited by excessive compressor cycling between the loaded and unloaded condition.

1.With service and supply system leakage below the maximum allowable limits and the vehicle parked, bring system pressure to governor cut-out and allow the engine to idle.

2.The compressor should remain unloaded for a minimum of 5-10 minutes. If compressor cycling occurs more frequently and service and supply system leakage is within tolerance replace the compressor or repair the compressor unloader system using a genuine Bendix maintenance kit available from authorized Bendix parts outlets.

COMPRESSOR REMOVAL & DISASSEMBLY

GENERAL

The following disassembly and assembly procedure is presented for reference purposes and presupposes that a rebuild or repair of the compressor is being undertaken. Several maintenance kits are available and the instructions provided with these parts and kits should be followed in lieu of the instructions presented here.

MAINTENANCE KITS & SERVICE PARTS
Cylinder Head Gasket Kit .......................................................	5008558
Unloader Kit ...........................................................................	5008557
Governor Adapter Kit .............................................................	5008561
Compressor Seal Kit (crankcase)...........................................	5008559
Components and kits for Caterpillar Engines
CAT C7/C9 Inlet Check Valve .................................................	801580
CAT C11/C13/C15/C18 Inlet Check Valve ...............................	801592
CAT C7/C9 Engine Seal Kit....................................................	5012367
CAT C11/C13/C15/C18 Engine Seal Kit.................................	5012369
CAT ST-4 Discharge Safety Valve (7/8"-14 thrd.) .....................	801116
Components and kits for DDC Engines
DDC Inlet Check Valve ............................................................	802192
DDC Series 60 Engine Seal Kit..............................................	5012371
DDC ST-4 Discharge Safety Valve (M16-1.5 thrd.)...................	800534

IMPORTANT! 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. Where speciﬁcally directed, the parking brakes may have to be released, and/or spring brakes caged, and this will require that the vehicle be prevented from moving by other means for the duration of these tests/procedures.

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. 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.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 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 lamp should be ON) prior to performing any vehicle maintenance where one or more wheels on a drive axle are lifted off the ground and moving.

1 Head Cap Screws (4)	2 Unloader Cover Cap Screws (2)
(include washers)	3 Unloader Cover Splash Shield
	3 Unloader Cover Splash Shield
4 Unloader Cover	6 Unloader Balance Piston
5 Unloader Cover Gasket	7 O-Ring
5 Unloader Cover Gasket	8 Spring
12 ST-4™ Safety Valve	9 O-Ring
12 ST-4™ Safety Valve	10 Unloader Piston
	10 Unloader Piston
	11 O-Ring
	14 Head Gasket
13 Cylinder Head	Alignment	(2)
	Bushings
15 Cooling	16 Valve Plate
Plate	Assembly

			30	31
			Governor	31
			Gasket (2)	Governor
17 Inlet Reed Valve/				Adapter
Gasket	19 Cylinder
	19 Cylinder
18 Cylinder	Rod
18 Cylinder
				32 Bolt
	Crankcase			with
	Crankcase			Washer
20 Bearing	Alignment			Washer
20 Bearing	Alignment			(2)
Sleeve	Pins			(2)
Sleeve	Pins
21 Crankcase	22 Crankshaft
	22 Crankshaft

27 Bottom Cover	23 Rear Bearing
27 Bottom Cover			24 O-Ring
Gasket				25 Rear End
				Cover

Item Qty. Description

14 Head Cap Screws

22 Unloader Cover Cap Screws

3	1	Unloader Cover Splash Shield					29 Cap		26 Cap
4**	1	Unloader Cover		28 Crankcase					26 Cap
4**	1	Unloader Cover							Screws (4)
5**	1	Unloader Cap Gasket				Screws (4)			Screws (4)
5**	1	Unloader Cap Gasket			Cover	Screws (4)
6**	1	Unloader Balance Piston			Cover
6**	1	Unloader Balance Piston
7**	1	O-Ring
8**	1	Spring
8**	1	Spring						Notes:
9**	1	O-Ring						Notes:
10**	1	Unloader Piston						*	included in Cylinder Head Gasket Kit
11**	1	O-Ring							(5008558)
12	1	ST-4™ Safety Valve	Item Qty.		Description			**	included in Unloader Kit (5008557)
13	1	Cylinder Head	23	1	Rear Bearing			**	included in Unloader Kit (5008557)
14*	2	Head Gaskets	24	1	O-Ring			***	included in Governor Adapter Kit
15	1	Cooling Plate	24	1	O-Ring			***	included in Governor Adapter Kit
15	1	Cooling Plate	25	1	Rear End Cover				(5008561)
16	1	Valve Plate Assembly	26	4	Cap Screws
17*	1	Inlet Reed Valve/Gasket	27	1	Bottom Cover Gasket			Crankcase Compressor Seal Kit (5008559)
18	1	Cylinder	28	1	Crankcase Cover			Crankcase Compressor Seal Kit (5008559)
18	1	Cylinder	28	1	Crankcase Cover			Unique Engine Seal Kits are available, for
19	1	Cylinder Rod	29	4	Cap Screws			Unique Engine Seal Kits are available, for
19	1	Cylinder Rod	29	4	Cap Screws			Cat C7/C9 Engine, Cat C11/C13/C15/C18
20	1	Sleeve Bearing	30***	2	Governor Gasket			Cat C7/C9 Engine, Cat C11/C13/C15/C18
20	1	Sleeve Bearing	30***	2	Governor Gasket			Engines, and DDC Series 60 Engines
21	1	Crankcase	31***	1	Governor Adapter			Engines, and DDC Series 60 Engines
22	1	Crankshaft	32***	2	Bolt with Washer
22	1	Crankshaft	32***	2	Bolt with Washer

FIGURE 13 – BA-921® COMPRESSOR EXPLODED VIEW

REMOVAL

In many instances it may not be necessary to remove the compressor from the vehicle when installing the various maintenance kits and service parts. The maintenance technician must assess the installation and determine the correct course of action.

These instructions are general and are intended to be a guide. In some cases additional preparations and precautions are necessary. In all cases follow the instructions contained in the vehicle maintenance manual in lieu of the instructions, precautions and procedures presented in this manual.

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 of the compressor. Identify and disconnect all air, water and oil lines leading to the compressor.

3.Remove as much road dirt and grease from the exterior of the compressor as possible.

4.Remove the discharge and inlet ﬁttings, if applicable, and note their position on the compressor to aid in reassembly.

Note: If a cylinder head maintenance kit is being installed, stop here and proceed to PREPARATION FOR DISASSEMBLY. If replacing the compressor continue.

5.Remove any supporting bracketing attached to the compressor and note their positions on the compressor to aid in reassembly.

6.Remove the front ﬂange mounting bolts and remove the compressor from the vehicle.

7.Inspect drive gear and associated drive parts for visible wear or damage. If the compressor drive gear is worn or damaged, the compressor must be replaced. Refer the Engine Manufacturers service manual to address the associated engine drive parts.

8.If the compressor is being replaced stop here and proceed to “Installing the Compressor” at the end of the assembly procedure. (Note: Replacement compressors come with the drive gear pre-assembled on the compressor.)

PREPARATION FOR DISASSEMBLY

Remove the balance of road dirt and grease from the exterior of the compressor with a cleaning solvent. If a rear end cover or end cover adapter is used on the compressor being worked on, mark it in relation to the crankcase. It is recommended, but not speciﬁcally necessary, to mark the relationships of the cylinder head (13), cooling plate (15), valve plate assembly (16), and crankcase (21).

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.

Prior to disassembly make certain that the appropriate kits and or replacement parts are available. Refer to Figure 13 during the entire disassembly and assembly procedure.

What follows is a description of a complete disassembly, actual maintenance may only need to include portions of these instructions.

CYLINDER HEAD

1.Remove the discharge safety valve (12) from the cylinder head (13).

2.To restrain the spring force exerted by balance piston spring (8) of the unloader assembly, hold the unloader cover (4) in place while removing the two unloader cover cap screws (2) and spray shield (3). Carefully release the hold on the unloader cover until the spring force is relaxed, then remove the unloader cover.

3.Remove the unloader cover gasket (5).

4.Remove the balance piston (6), its spring (8) and the unloader piston (10) along with its o-rings (7, 9 & 11) from the cylinder head (13).

5.Remove the four hex head bolts (1) from the cylinder head.

6.Gently tap the cylinder head, cooling plate (15) and valve plate assembly (16) with a soft mallet to break the gasket seal between the valve plate assembly and the crankcase (21). Lift the cylinder head with cooling plate and valve plate assembly off the crankcase.

7.Remove the metal inlet reed valve/gasket (17).

8.Gently tap the cylinder head, cooling plate and valve plate assembly with a soft mallet to break the gasket seals. Then separate the cylinder head from the cooling plate (15) and valve plate assembly and remove the two gaskets (14) between them.

CRANKCASE COVER

1.Remove the four crankcase cover cap screws (29) securing the crankcase cover (28) to the crankcase (21). Using a soft mallet, gently tap the crankcase cover to break the gasket seal. Remove the crankcase cover gasket (27).

2.In the case of the Caterpillar C11 and C13 engine application, the BA-921® compressor utilizes an “oil jet” that sprays oil under the piston for purposes of cooling. This oil jet is part of a special crankcase cover that is used strictly on the BA-921® compressor for the C11 and C13 engine installation (Figure 11). Refer to section OPERATION – Lubrication for description of the system. To disassemble, follow the instructions below.

a.Remove the oil supply line from the engine at the inlet to the special crankcase cover.

b.Remove the metal oil supply tube at the compressor oil supply port and at the outlet ﬁtting of the special crankcase cover.

NOTE: Mark position of the special crankcase cover. It must be re-installed with the same orientation to assure proper operation of the oil jet.

c.Remove the four crankcase cover cap screws securing the special crankcase cover to the crankcase. Using a soft mallet, gently tap the crankcase cover to break the gasket seal. Remove the crankcase cover gasket (27).

REAR END COVER

1.Remove the four end cover cap screws (26) that secure the rear end cover to the crankcase.

2.Remove the rear end cover from the crankcase. Remove the o-ring seal (24) from the end cover.

CLEANING OF PARTS GENERAL

All parts should be cleaned in a good commercial grade of solvent and dried prior to inspection.

CYLINDER HEAD ASSEMBLY

1.Carefully remove all gasket material adhering to the cylinder head (13), cooling plate (15), valve plate assembly (16) and cast iron crankcase (21). Make certain not to scratch or mar the gasket surfaces. Pay particular attention to the gasket surfaces of the head.

2.Remove carbon deposits from the discharge and inlet cavities of the cylinder head, cooling plate and valve plate assembly. They must be open and clear in both assemblies. Make certain not to damage the head.

3.Remove rust and scale from the cooling cavities and passages in the cylinder head, cooling plate and valve plate assembly and use shop air to clear debris from the passages.

4.Check the threads in all cylinder head ports for galling (e.g. abrasion, chaﬁng). Minor thread chasing (damage) is permitted.

5.Make certain the unloader vent passage under the unloader cover (4) in the head is open and free of debris.

INSPECTION OF PARTS

CYLINDER HEAD, COOLING PLATE, VALVE PLATE ASSEMBLY AND UNLOADER MECHANISM

1.Carefully inspect the head gasket surfaces on the cylinder head (13) for deep gouges and nicks. Also, inspect the cylinder head for any cracks or port thread damage. If detected, the compressor must be replaced. If large amounts of carbon build-up are present in the discharge cavity such that it restricts the air ﬂow through the cylinder head, the compressor should be replaced.

2.Carefully inspect both sides of the head gasket surfaces on the cooling plate (15) for deep gouges and nicks. Also, inspect the cooling plate for any cracks or other damage. If found, the compressor must be replaced.

3.Carefully inspect the valve plate assembly (16) gasket surfaces (both sides) for deep gouges and nicks. Pay particular attention to the gasket surface. An inlet reed valve/gasket (17) is used between the valve plate assembly and crankcase. This gasket surface must be smooth and free of all but the most minor scratches. If excessive marring or gouging is detected, the compressor must be replaced. If large amounts of carbon build-up are present on the two main surfaces, in the two discharge valve holes or between the discharge valve and the discharge seat, the compressor should be replaced.

4.If the unloader assembly has been removed from the cylinder head, the unloader assembly must be serviced using an unloader kit (5008557).

5.If large amounts of carbon build-up are present on the unloader piston (10) seat or oriﬁce or if the return spring exhibits compression set, the unloader components must be replaced with an unloader kit.

REAR END COVER

Check for cracks and external damage. Check the crankshaft rear bearing diameter in the rear end cover (25) for excessive wear, ﬂat spots or galling. Check the rear support bracket threaded holes and hydraulic pump attachment threaded holes (if present) for thread damage. Minor thread chasing is permitted but do not re-cut the threads. If any of these conditions are found, replace the compressor.

CRANKCASE

Check the cylinder head gasket surface on the deck (top) of the crankcase (21) for nicks, gouges, and marring. A metal gasket is used to seal the cylinder head to the crankcase. This surface must be smooth and free of all but the most minor scratching. If excessive marring or gouging is detected, the compressor 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 re-torque after initial assembly torques fall unless instructed otherwise. A compiled listing of torque speciﬁcations is presented on page 14.

INCH POUNDS TO FOOT POUNDS

To convert inch pounds to foot pounds of torque, divide inch pounds by 12.

Example:	12 Inch Pounds = 1 Foot Pound
	12

FOOT POUNDS TO INCH POUNDS

To convert foot pounds to inch pounds of torque, multiply foot pounds by 12.

Example: 1 Foot Pound x 12 = 12 Inch Pounds

CRANKCASE COVER

1.Position the crankcase cover gasket (27) on either the crankcase or crankcase cover and install the crankcase cover on the crankcase using the four cap screws. “Snug” all four cap screws then torque to 62-71 inch pounds (7-8 Nm) using a crossing pattern.

2.In the case of the Caterpillar C11 and C13 engine application, the compressor utilizes an “oil jet” that sprays oil under the piston for purposes of cooling. This oil jet is part of a special crankcase cover that is used strictly on the compressor for the C11 and C13 engine installation (Figure 14). Refer to section OPERATION

– Lubrication for description of the system. To reassemble, follow the instructions below.

a.Position the gasket (27) on either the crankcase or the special crankcase cover and install the special crankcase cover on the crankcase using the four cap screws. Note: Make sure that the cover is orientated in its original position. “Snug” all four cap screws then torque to 62-71 inch pounds (7-8 Nm) using a crossing pattern.

b.Assuming that the ﬁttings at the outlet of the special crankcase cover and compressor oil supply port had not been removed (ﬁttings still torqued in place), position both ends of the metal tube over the two ﬁttings and run the ﬁttings down to ﬁnger tight then torque to 130 - 150 inch pounds (16 – 17.5 Nm). If a torque wrench is not available, run ﬁttings down to ﬁnger tight. Then tighten the ﬁttings ¼ to ½ turns.

Side View

Compressor

Oil Supply

Port

Engine

Oil Supply

Line

Pre-formed

Metal

Oil Supply

Tube

Lubricating

Oil outlet

Lubricating Oil

From the Engine

Enters Here

Crankcase Cover with

Oil Jet Assembly

FIGURE 14 – VIEWS OF SPECIAL CRANKCASE COVER WITH OIL JET ASSEMBLY FOR CAT C11/C13 ENGINE APPLICATIONS

REAR END COVER (If Present)

1.Install the o-ring (24) on the rear end cover.

2.Orient the rear end cover (25) to the crankcase using the reference marks made during disassembly. Carefully install the rear end cover in the crankcase making certain not to damage the crankshaft bearing surface.

3.Install the four end cover cap screws (26) or studs. “Snug” the screws then tighten to 195 to 213 inch pounds (22-24 Nm) using a crossing pattern.

CYLINDER HEAD

1.Note the position of the protruding crankcase alignment pins on the deck (top) of the crankcase (21). Install the metal inlet reed valve/gasket (17) over the alignment pins on the crankcase.

2.Position the valve plate assembly (16) on the crankcase so that the alignment pins in the crankcase ﬁt into the corresponding holes in the valve plate assembly.

3.Position one of the embossed metal head gaskets (14) over the alignment bushings protruding from the cooling plate. Position the second embossed metal head gasket over the alignment bushings on the opposite side of the cooling plate (15). When properly positioned, the outline of the two embossed gaskets match the outline of the cooling plate.

4.Install the cooling plate with the head gaskets onto valve plate assembly by lining up the alignment bushings on the cooling plate over oversized countersunk holes of the valve plate assembly. Again, when properly installed, the outline of the cooling plate matches the outline of the valve plate assembly.

5.Position and install the cylinder head (13) over the alignment bushings protruding from the cooling plate. When properly installed, the outline of the cylinder head assembly will match the outline of the cooling plate and valve plate assembly.

Note: To assist with correct installation, the alignment bushings only ﬁt into two of the four cylinder head bolt holes.

6.Install the four hex head cylinder head bolts (1) and snug them, then tighten evenly to a torque of 265 to 292 inch pounds (30-33 Nm) using a crossing pattern.

7.Apply a coating of the lubricant provided in the unloader kit into the unloader bore (both diameters). Apply additional lubricant to the three o-ring grooves on the unloader piston (10). Note that the o-ring (7) installs inside the top of the unloader piston. Install the three o-rings (7, 9, 11) into the appropriate o-ring grooves on the unloader piston (10). Apply another coating of the lubricant onto the exposed o-ring surfaces and onto the large diameter of the balance piston (6). Install the unloader piston with the pre-installed o-rings into the cylinder head unloader bore making certain not to damage them in the process.

8.Install the balance piston spring (8) in the unloader piston.

9.Apply a coating of lubricant to the largest diameter of the balance piston. Install the small diameter end of the balance piston through the center of the spring.

10.Install the unloader cover gasket (5) on the cylinder head making certain both screw holes align.

11.Position the unloader cover (4) on top of the balance piston making certain the stamped logo is visible.

12.Press and hold the unloader cover in place on the cylinder head, place the spray shield (3) over the outboard hole (in order to cover the vent slot in the unloader cap). Install both unloader cover cap screws

(2). Torque the cover cap screws (2) to 62 to 71 inch pounds (7-8 Nm).

INSTALLING THE COMPRESSOR

1.Install the appropriate gasket or o-ring on the front ﬂange of the compressor. Make certain oil supply or return holes in the gasket are properly aligned with the compressor and engine. On the Detroit Diesel S60 engine installations, an additional o-ring is required to seal the oil feed passageway between the compressor and engine gear case cover. Gasket sealants are

not recommended. Secure the compressor on the engine and tighten the mounting bolts per Engine Manufacturers recommended torque requirements.

2.Install any supporting brackets on the compressor in the same position(s) noted and marked during removal. If a rear support bracket was on the original installation, hand tighten the bolts on both ends before torquing the bolts. Note: It is important that the rear support bracket is ﬂush to both surfaces before the bolts are torqued.

3.Inspect all air, oil, and coolant lines and ﬁttings before reconnecting them to the compressor. Make certain o-ring seals are in good or new condition, the threads are clean and the ﬁttings are free of corrosion. Replace as necessary.

4.Install the discharge, inlet, coolant and governor adapter ﬁttings, if applicable, in the same position on the compressor noted and marked during disassembly. See the Torque Speciﬁcations for various ﬁtting sizes and types of thread at the rear of this manual. Tighten all hose clamps.

5.Before returning the vehicle to service, perform the Operation and Leakage Tests speciﬁed in this manual. Pay particular attention to all lines and hoses disconnected during the maintenance and check for air, oil, and coolant leaks at compressor connections. Also check for noisy operation.

TESTING THE REBUILT COMPRESSOR

In order to properly test a compressor under operating conditions, a test rack for correct mounting, cooling, lubricating, and driving the compressor is necessary. Such tests are not compulsory if the unit has been carefully rebuilt by an experienced person. A compressor efﬁciency or build-up test can be run which is not too difﬁcult. An engine lubricated compressor must be connected to an oil supply line of at least 15psi pressure during the test and an oil return line must be installed to keep the crankcase drained. Connect to the compressor discharge port, a reservoir with a volume of 1500 cubic inches, including the volume of the connecting line. With the compressor operating at 2100 RPM, the time required to raise the reservoir(s) pressure from 85 psi to 100 psi should not exceed 5 seconds. During this test, the compressor should be checked for gasket leakage and noisy operation, as well as unloader operation and leakage. If the compressor functions as indicated, reinstall on the vehicle connecting all lines as marked in the disassembly procedure.

BA-921® COMPRESSOR SPECIFICATIONS

Typical weight .........................................................................	37 lbs.
Number of cylinders .........................................................................	1
Bore Diameter .......................................................	3.622 in. (92 mm)
Stroke ...................................................................	2.126 in. (54 mm)
Calculated displacement at 1250 RPM ..............................	15.8 CFM
Flow Capacity @ 1800 RPM & 120 PSI ...............................	11.6 CFM
Flow Capacity @ 3000 RPM & 120 PSI ...............................	16.5 CFM
Approximate horsepower required:
Loaded 1800 RPM at 120 PSIG...............................................	4.6 HP
Unloaded 1800 RPM................................................................	0.8 HP
Minimum coolant ﬂow at maximum RPM .....................	2.5 Gals./Min.
Maximum inlet air temperature .................................................	250°F
Maximum discharge air temperature ........................................	400°F
Minimum oil pressure required .................................................	15 PSI
Minimum oil-supply line size ................................................	3/16" I.D.
Minimum unloader-line size .................................................	3/16" I.D.
Minimum Governor Cut-out Pressure......................................	120 PSI

TORQUE SPECIFICATIONS

Assembly Torques in inch pounds (in. Ibs.)

M8x1.25-6g Cylinder Head....................	265-292 In. Lbs. (30-33 Nm)
M5x0.75-6g Unloader Cap ............................	62-71 In. Lbs. (7-8 Nm)
M8x1.25-6g Governor Adapter..............	195-213 In. Lbs. (22-24 Nm)
M8x1.25-6g Rear End Cover.................	195-213 In. Lbs. (22-24 Nm)
M6x1.00-6g Crankcase Cover .....................	62-71 In. Lbs. (7-8 Nm)
Inlet Port Fittings
1 3/16"-12 UN-2B (Aluminum Cylinder Head)
straight ﬁtting.......................................	841-925 In. Lbs.	(95-104 Nm)
adjustable (w/ jam nut) ..........................	597-655 In. Lbs.	(67-74 Nm)
M27x2-6g (Cast Iron Cylinder Head). 885-980 In. Lbs. (100-111 Nm)
Discharge Port Fittings
7/8"-14 UNF-2B (Aluminum Cylinder Head)
straight ﬁtting.........................................	509-553 In. Lbs.	(57-62 Nm)
adjustable (w/ jam nut) ..........................	354-389 In. Lbs.	(40-44 Nm)
M22 x 1.5-6g (Cast Iron Cylinder Head) 531-575 In. Lbs.		(60-65 Nm)
Water Port Fittings
3/4"-16 UNF-2B (Aluminum Cylinder Head)
straight ﬁtting.........................................	265-292 In. Lbs.	(30-33 Nm)
adjustable (w/ jam nut) ..........................	248-274 In. Lbs.	(28-31 Nm)
M18 x 1.5-6g (Cast Iron Cyliner Head)	.. 354-395 In. Lbs.	(40-45 Nm)
Unloader Port Fittings
1/8"-27 NPT .......................................................................		2 - 3 TFFT1
M10 x 1.5-6g.........................................	120-145 In. Lbs. (14-16 Nm)
Safety Valve Port
7/8"-14 UNF-2B ....................................	230-257 In. Lbs. (26-29 Nm)
M16x1.5-6H ..........................................	230-257 In. Lbs. (26-29 Nm)
Oil Port
7/16"-16 UNF ........................................	150-170 In. Lbs. (17-19 Nm)
Special Attachments – Cat C11/C13 Engine Crankcase Cover
w/ Oil Jet and Associated Hardware (Figure 14)
1) Crankcase Cover (In/Out) Oil Fittings
7/16"-16 UNF ....................................	150-170 In. Lbs. (17-19 Nm)
2) Compressor Oil Supply Fitting
7/16"-16 UNF ....................................	150-170 In. Lbs. (17-19 Nm)
3) Metal Tube (Tube Ends)
7/16"-16 UNF ................................	130-150 In. Lbs. (16-17.5 Nm)

Option: Run ﬁttings down ﬁnger tight. Tighten ¼ to ½ turns.

1 Note: TFFT = Turns From Finger Tight

Advanced Troubleshooting Guide for Air Brake Compressors

INDEX

Symptom	Page Number
Air
Air brake charging system:
Slow build (9.0) .....................................	23 - 24
Doesn’t build air (10.0).................................	25
Air dryer:
Doesn’t purge (14.0) ....................................	26
Safety valve releases air (12.0) ...................	26
Compressor:
Constantly cycles (15.0) ..............................	26
Leaks air (16.0)............................................	27
Safety valve releases air (11.0) ...................	25
Noisy (18.0) ................................................	27
Reservoir:
Safety valve releases air (13.0) ...................	26

Symptom	Page Number
Coolant
Compressor leaks coolant (17.0).......................		27
Engine
Oil consumption (6.0) .......................................		23
Oil
Oil Test Card results (1.0)..................................		18
Oil is present:
On the outside of the compressor (2.0)		....... 19
At the air dryer purge/exhaust
or surrounding area (3.0).........................		19
In the supply reservoir (4.0) ..................		20 - 22
At the valves (5.0)........................................		22
At air dryer cartridge (7.0)............................		23
In the ping tank or compressor
discharge aftercooler (8.0).......................		23

	Test Procedures		Maintenance & Usage Guidelines
(1)	Oil Leakage at Head Gasket	........ 28	Maintenance Schedule and
(2)	System Leakage ..........................	28	Usage Guidelines (Table A).......	17
(3)	Compressor Discharge and
	Air Dryer Inlet Temperature ...........	29
(4)	Governor Malfunction ...................	28
(5)	Governor Control Line ..................	29
(6)	Compressor Unloader ..................	29
BASIC™ Test Information ..............		30-32

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 compressor is typically cooled by the 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. When the air pressure becomes greater than that of the preset “cut-out”, the governor controls the unloader mechanism of the compressor to stop the compressor from building air and also causes the air dryer to purge. As the service reservoir air pressure drops to the “cut-in” setting of the governor, the governor returns the 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 building air to the total engine running time. Air compressors 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 additional maintenance. Factors that add to the duty cycle are: air suspension, additional air accessories, use of an undersized compressor, 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 17) 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 remove most of the charging system 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 from the compressor to the air dryer inlet ﬁtting to avoid 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 33-35). Shorter discharge line lengths or insulation may be required in cold climates.

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 water collected are automatically 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® system ﬁlter, designed to minimize the amount of oil present.

Discharge	Optional “Ping” Tank
Line	Air Dryer

Compressor

Governor

The Air Brake Charging System supplies the compressed air for the braking system as well as other air accessories for the vehicle. The system usually consists of an air compressor, governor, discharge line, air dryer, and service reservoir.

Optional Bendix® PuraGuard®

System Filter or PuraGuard QC™

Oil Coalescing Filter

(Governor plus Synchro valve	Service Reservoir
for the Bendix® DuraFlo™ 596	(Supply Reservoir)
Compressor)	Reservoir Drain
	Reservoir Drain

Table A: Maintenance Schedule and Usage Guidelines

Regularly scheduled maintenance is the single most important factor in maintaining the air brake charging

Column 1

Column 2

Column 3

Column 4

Column 5

Typical

Discharge

Recom-

Acceptable

mended

Reservoir

Vehicle Used for:

Compressors

Line

Air Dryer

Reservoir

Oil Contents3

Axles

(See footnote 7)

I.D.

Length

Replacement1

Schedule2

Drain Interval

No. of

Spec'd

Cartridge

Drain

at Regular

Low Air Use

1/2 in.

6 ft.

Compressor with less than 15% duty

BASIC™ test

cycle

For oil

carry-over

acceptable

e.g. Line haul single trailer

<![if ! IE]>

<![endif]>compressor

Month -

See

w/o air suspension, air over

control

suggested

Recom-

range:

hydraulic brakes.

less

upgrades:

mended

3 oil units

5/8 in.

9 ft.

Every 3

Every

per month.

<![if ! IE]>

<![endif]>air

Years

appendix

Compressor with up to 25% duty cycle

<![if ! IE]>

<![endif]>compressor

1/2 in.

9 ft.

Max of ev-

e.g. Line haul single trailer

<![if ! IE]>

<![endif]>550Flo-Tu®®

For oil carry-over

ery 90 days

with air suspension,

school bus.

less

control4 suggested

upgrades:

<![if ! IE]>

<![endif]>921-® air

<![if ! IE]>

<![endif]>Bendix

5/8 in.

12 ft.

For the

Order

BASIC™

High Air Use

Test Kit:

Compressor with up to 25% duty cycle

<![if ! IE]>

<![endif]>compressorair

<![if ! IE]>

<![endif]>Bendix® BA

Every 2

Bendix

terminal jockey, off-highway,

P/N

e.g. Double/triple trailer, open

5013711

highway coach/RV, (most)

1/2 in.

12 ft.

pick-up & delivery, yard or

construction, loggers, concrete

<![if ! IE]>

<![endif]>750

For oil carry-over

Years

control4 suggested

mixer, dump truck, ﬁre truck.

less

<![if ! IE]>

<![endif]>Bendix® Tu-Flo®

upgrades:

<![if ! IE]>

<![endif]>compressor

5/8 in.

15 ft.

BASIC™ test

5 oil units

acceptable

range:

<![if ! IE]>

<![endif]>air

Every

per month.

Month

Compressor with up to 25% duty cycle

<![if ! IE]>

<![endif]>596

See

e.g. City transit bus, refuse,

<![if ! IE]>

<![endif]>™

appendix

bulk unloaders, low boys,

<![if ! IE]>

<![endif]>DuraFlo

3/4 in.

12 ft.

urban region coach, central

Every

tire inﬂation.

<![if ! IE]>

<![endif]>®, or

Year

less

<![if ! IE]>

<![endif]>Bendix® BA-922

Footnotes:

Bulletins TCH-08-21 and TCH-08-22, included in Appendix B, for

1. With increased air demand the air dryer cartridge needs to be

replaced more often.

more information.)

Use the drain valves to slowly drain all reservoirs to zero psi.

For certain vehicles/applications, where turbo-charged inlet air is

3. Allow the oil/water mixture to fully settle before measuring oil

used, a smaller size compressor may be permissible.

quantity.

Note: Compressor and/or air dryer upgrades are recommended

To counter above normal temperatures at the air dryer inlet, (and

in cases where duty cycle is greater than the normal range (for

resultant oil-vapor passing upstream in the air system) replace the

the examples above).

discharge line with one of a larger diameter and/or longer length.

For correct compressor upgrades consult Bendix - Please note

This helps reduce the air's temperature. If sufﬁcient cooling occurs,

that because a compressor is listed in the same area of the chart

the oil-vapor condenses and can be removed by the air dryer.

does not necessarily mean that it would be a suitable candidate

Discharge line upgrades are not covered under warranty.

Note:

for upgrade purposes.

To help prevent discharge line freeze-ups, shorter discharge line

For Bendix® Tu-Flo® 550 and 750 compressors, unloader service is

lengths or insulation may be required in cold climates. (See Bendix

recommended every 250,000 miles.

Air Brake Charging System Troubleshooting

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.

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, 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 with moving, rotating, leaking, heated or electrically charged components.

Look for:

Normal - Charging system is working within normal range.

Check - Charging system needs further investigation.

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.

10.Prior to returning the vehicle to service, make certain all components and systems are restored to their proper operating condition.

Symptom:	What it may indicate:	What you should do:

1.0 Oil Test Card	Not a valid test.
Results

Bendix®

BASIC™ Test

Discontinue using this test.

Do not use this card test to diagnose compressor "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 30 for a flowchart and expanded explanation of the checklist used when conducting the BASIC™ test.)

Symptom:	What it may indicate:	What you should do:

2.0Oil on the Outside of the Compressor

2.1Oil leaking at compressor / engine connections:

2.2 Oil leaking from compressor:

Engine and/or other accessories	Find the source and repair. Return the vehicle
leaking onto compressor.	to service.
(a) Leak at the front or rear (fuel	Repair or replace as necessary. If the
pump, etc.) mounting ﬂange.	mounting bolt torques are low, replace the
	gasket.
(b) Leak at air inlet ﬁtting.	Replace the ﬁtting gasket. Inspect inlet
	hose and replace as necessary.
(c) Leak at air discharge ﬁtting.	Replace gasket or ﬁtting as necessary to
	ensure good seal.
(d) Loose/broken oil line ﬁttings.	Inspect and repair as necessary.
(a)Excessive leak at head gasket.	Go to Test 1 on page 28.

	(b)Leak at bottom cover plate.	Reseal bottom cover plate using RTV
		silicone sealant.
	(c) Leak at internal rear flange	Replace compressor.
	gasket.	Replace compressor.
	(d)Leak through crankcase.	Replace compressor.
	(d)Leak through crankcase.	Clean compressor and check periodically.
	(e)(If unable to tell source of leak.)	Clean compressor and check periodically.
	(e)(If unable to tell source of leak.)

(a)

Head gaskets and rear ﬂange gasket

(c)locations.

3.0 Oil at air dryer purge/exhaust or surrounding area

Air brake charging system functioning normally.

Air dryers remove water and oil from the air brake charging system.

Check that regular maintenance is being performed. Return the vehicle to service. An optional kit (Bendix piece number 5011327 for the Bendix® AD-IS® or AD-IP™ air dryers, or 5003838 for the Bendix® AD-9™ air dryer) is available to redirect the air dryer exhaust.

	Symptom:	What it may indicate:	What you should do:

4.0 Oil in Supply or Service Reservoir (air dryer installed)

(If a maintained Bendix® PuraGuard® system ﬁlter or Bendix® PuraGuard QC™ oil coalescing

ﬁlter is installed, call 1-800-AIR-BRAKE (1-800-247-2725) and speak to a Tech Team member.)

See Table A, on page 17, for maintenance schedule information.

Maintenance

(a)If air brake charging system maintenance has not been performed.

That is, reservoir(s) have not been drained per the schedule in Table A on page 17, Column 4 and/or the air dryer maintenance has not been performed as in Column 3.

(b)If the vehicle maintenance has been performed as recommended in Table A on page 17, some oil in the reservoirs is normal.

(a)

Drain all air tanks (reservoirs) into the Bendix® BASIC™ test cup. (Bendix kit P/N 5013711).

Duty cycle too high

Drain all air tanks and check vehicle at next service interval using the Bendix® BASIC™ test. See Table A on page 17, column 3 and 4, for recommended service schedule.

Drain all air tanks into Bendix® BASIC™ test cup (Bendix Air System Inspection Cup). If less than one unit of reservoir contents is found, the vehicle can be returned to service. Note: If more than one oil unit of water (or a cloudy emulsion mixture) is present, change the vehicle's air dryer, check for air system leakage (Test 2, on page 28), stop inspection and check again at the next service interval.

See the BASIC™ test kit for full details.

If less than one "oil unit" of water (or water/ cloudy emulsion mixture) is present, use the BASIC™cup chart on the label of the cup to determine if the amount of oil found is within the acceptable level.

If within the normal range, return the vehicle to service. For vehicles with accessories that are sensitive to small amounts of oil, consider a Bendix® PuraGuard QC™ oil coalescing ﬁlter.

If outside the normal range go to Symptom 4.0(c).

Also see the Table A on page 17, column 3 for recommended air dryer cartridge replacement schedule.

(c)Air brake system leakage.

(d)Compressor may be undersized for the application.

The duty cycle is the ratio of time the compressor spends building air to total engine running time. Air compressors are designed to build air (to "run loaded") up to 25% of the time. Higher duty cycles cause conditions that affect air 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 undersized compressor, frequent stops, excessive leakage from ﬁttings, connections, lines, chambers or valves, etc.

Go to Test 2 on page 28.

See Table A, column 1, on page 17 for recommended compressor sizes.

If the compressor is "too small" for the vehicle's role (for example, where a vehicle's use has changed or service conditions exceed the original vehicle or engine OE spec's) then upgrade the compressor. Note: The costs incurred (e.g. installing a larger capacity compressor, etc.) are not covered under original compressor warranty.

If the compressor is correct for the vehicle, go to Symptom 4.0 (e).

Symptom:	What it may indicate:	What you should do:

4.0 Oil in Supply or Service Reservoir*

(air dryer installed) (continued)

(e)

Temperature

(e)Air compressor discharge and/or air dryer inlet temperature too high.

(f)Insufﬁcient coolant ﬂow.

(f)

Testing the temperature	Inspecting the coolant hoses.
at the discharge ﬁtting.
	(g) Restricted discharge line.

(g)

Kinked discharge line shown.

Other

Check temperature as outlined in Test 3 on page 28. If temperatures are normal go to 4.0(h).

Inspect coolant line. Replace as necessary (I.D. is 1/2").

Inspect the coolant lines for kinks and restrictions and ﬁttings for restrictions. Replace as necessary.

Verify coolant lines go from engine block to compressor and back to the water pump. Repair as necessary.

If discharge line is restricted or more than 1/16" carbon build-up is found, replace the discharge line. See Table A, column 2, on page 17 for recommended size. Replace as necessary.

The discharge line must maintain a constant slope down from the compressor to the air dryer inlet ﬁtting to avoid 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 freezeups, see Bendix Bulletins TCH-08-21 and TCH-08-22 (Appendix B). Shorter discharge line lengths or insulation may be required in cold climates.

(h)Restricted air inlet (not enough air to compressor).

(h)

Partly collapsed inlet line shown.

Check compressor air inlet line for restrictions, brittleness, soft or sagging hose conditions etc. Repair as necessary. Inlet line size is 3/4 ID. Maximum restriction requirement for compressors is 25 inches of water.

Check the engine air ﬁlter and service if necessary (if possible, check the air ﬁlter usage indicator).

*If a maintained Bendix® PuraGuard® system ﬁlter or Bendix® PuraGuard QC™ oil coalescing ﬁlter is installed, call 1-800-AIR-BRAKE (1-800-247-2725) and speak to a Tech Team member.

Symptom:	What it may indicate:	What you should do:

4.0 Oil in Supply or Service Reservoir*

(air dryer installed) (continued)

Other (cont.)

(i)Poorly filtered inlet air (poor air quality to compressor).

Inspect the engine air cleaner.

(j)Governor malfunction or setting.

(k)Compressor malfunction.

Crankcase Flooding

Consider installing a compressor bottom drain kit (where available) in cases of chronic oil passing where all other operating conditions have been investigated. Bendix compressors are designed to have a 'dry' sump and the presence of excess oil in the crankcase can lead to oil carryover.

Check for leaking, damaged or defective compressor air inlet components (e.g. induction line, ﬁttings, gaskets, ﬁlter bodies, etc.). Repair inlet components as needed. Note: Dirt ingestion will damage compressor and is not covered under warranty.

Go to Test 4 on page 29.

If you found excessive oil present in the service reservoir in step 4.0 (b) above and you did not ﬁnd any issues in steps 4.0 (c) through 4.0 (j) above, the compressor may be passing oil.

Replace compressor. If still under warranty, follow normal warranty process. Note: After replacing a compressor, residual oil may take a considerable period of time to be ﬂushed from the air brake system.

*If a maintained Bendix® PuraGuard® system ﬁlter or Bendix® PuraGuard QC™ oil coalescing ﬁlter is installed, call 1-800-AIR-BRAKE (1-800-247-2725) and speak to a Tech Team member.

5.0 Oil present at valves (e.g. at exhaust, or seen during servicing).

Air brake system valves are required to tolerate a light coating of oil.

A small amount of oil does not affect SAE J2024** compliant valves.

Check that regular maintenance is being performed and that the amount of oil in the air tanks (reservoirs) is within the acceptable range shown on the Bendix® BASIC™ test cup (see also column 5 of Table A on page 17). Return the vehicle to service.

For oil-sensitive systems, see page 16.

**SAE J2024 outlines tests all air brake system pneumatic components need to be able to pass, including minimum levels of tolerance to contamination.

Genuine

Bendix valves are all SAE J2024 compliant.

Symptom:	What it may indicate:	What you should do:

6.0 Excessive oil consumption in engine.

A problem with engine or other engine	See engine service manual.
accessory.

The engine service manual has more information.

7.0 Oil present	Air brake charging system is functioning
at air dryer	normally.
cartridge during
cartridge during
maintenance.
		Oil shown
		leaking
		from an
		air dryer
		cartridge.

Air dryers remove water and oil from the air brake charging system. A small amount of oil is normal. Check that regular maintenance is being performed and that the amount of oil in the air tanks (reservoirs) is within the acceptable range shown by the BASIC™ test (see also column 5 of Table A on page 17). Replace the air dryer cartridge as needed and return the vehicle to service.

8.0 Oil in ping tank or compressor discharge aftercooler.

Air brake charging system is functioning	Follow vehicle O.E. maintenance
normally.	recommendation for these components.

9.0 Air brake	(a) Air brake charging system	Using dash gauges, verify that the
charging system	functioning normally.	compressor builds air system pressure
seems slow to		from 85-100 psi in 40 seconds or less with
build pressure.		engine at full governed rpm. Return the
build pressure.		engine at full governed rpm. Return the
		vehicle to service.
	(b) Air brake system leakage.	Go to Test 2 on page 28.
	(c) Compressor may be undersized for	See Table A, column 1, on page 17 for some
	the application.	typical compressor applications. If the
		compressor is "too small" for the vehicle's
		role, for example, where a vehicle's use has
		changed, then upgrade the compressor.
		Note: The costs incurred (e.g. installing
		a larger capacity compressor, etc.) are
		not covered under original compressor
		warranty.
	(d) Compressor unloader mechanism	Go to Test 6 on page 29.
	malfunction.
	(e) Damaged compressor head	An air leak at the head gasket may indi-
	gasket.	cate a downstream restriction such as a
		freeze-up or carbon blockage and/or could
		indicate a defective or missing safety valve.
		Find blockage (go to 9.0(f) for details) and
		then replace the compressor. Do not re-
		use the safety valve without testing. See
		Symptom 12.0(a).

Symptom:	What it may indicate:	What you should do:

9.0 Air brake	(f) Restricted discharge line.
charging system
seems slow to
build pressure.
(continued)


		(f)
		(f)

Dash gauges.

Kinked discharge line shown.

Engine Oil Quality

Inadequate oil change intervals, the formulation of the oil and/or the quality of oil ﬁlter used can all lead to poor oil quality. These can increase the rate at which carbon builds up in the discharge line. Bendix recommends oil soot (solids) be maintained at less than 3%.

(g) Restricted air inlet (not enough air

to compressor).

(g)

Partly collapsed

inlet line shown. (h) Poorly filtered inlet air (poor air quality to compressor).

(i) Compressor malfunction.

If discharge line is restricted:

By more than 1/16" carbon build-up, replace the discharge line (see Table A, column 2, on page 17 for recommended size) and go to Test 3 on page 28.

By other restrictions (e.g. kinks). Replace the discharge line. See Table A, column 2, on page 17 for recommended size. Re test for air build. Return vehicle to service or, if problem persists, go to 9.0(a).

The discharge line must maintain a constant slope down from the compressor to the air dryer inlet ﬁtting to avoid 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 (Appendix B). Shorter discharge line lengths or insulation may be required in cold climates.

Check compressor air inlet line for restrictions, brittleness, soft or sagging hose conditions etc. Repair as necessary. Refer to vehicle manufacturer’s guidelines for inlet line size.

Check the engine air ﬁlter and service if necessary (if possible, check the air ﬁlter usage indicator).

Replace the compressor only after making certain that none of the preceding conditions, 9.0 (a) through 9.0 (h), exist.

Symptom:	What it may indicate:	What you should do:

10.0 Air charging (a) Governor malfunction*. system doesn’t

build air. (b) Restricted discharge line.

(c)Air dryer heater malfunction: exhaust port frozen open.

(d)Compressor malfunction.

*Note: For the Bendix® DuraFlo™ 596 air compressor, not only the governor, but also the SV-1™ synchro valve used would need to be tested. See Bulletin TCH-001-048.

Go to Test 4 on page 29.

See 9.0(f).

Replace air dryer heater.

Replace the compressor only after making certain the preceding conditions do not exist.

11.0 Compressor (a) Restricted discharge line. safety valve

releases air (Compressor

builds too much air).

Damaged discharge line shown.

(b)Downstream air brake system check valves or lines may be blocked or damaged.

(c)Air dryer lines incorrectly installed.

(d)Compressor safety valve malfunction.

(e)Compressor unloader mechanism malfunction.

(f)Governor malfunction.

If discharge line is restricted:

By more than 1/16" carbon build-up, replace the discharge line (see Table A, column 2, on page 17 for recommended size) and go to Test 3 on page 28.

By other restrictions (e.g. kinks). Replace the discharge line. See Table A, column 2, on page 17 for recommended size.

The discharge line must maintain a constant slope down from the compressor to the air dryer inlet ﬁtting to avoid 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 freezeups, see Bendix Bulletins TCH-08-21 and TCH-08-22 (Appendix B). Shorter discharge line lengths or insulation may be required in cold climates.

Inspect air lines and verify check valves are operating properly.

Ensure discharge line is installed into the inlet of the air dryer and delivery is routed to the service reservoir.

Verify relief pressure is 250 psi. Replace if defective.

Go to Test 6 on page 29.

Go to Test 4 on page 29.

Symptom:	What it may indicate:	What you should do:

12.0 Air dryer	(a) Restriction between air dryer and
safety valve	reservoir.
releases air.

Inspect delivery lines to reservoir for restrictions and repair as needed.

		(b) Air dryer safety valve	Verify relief pressure is at vehicle or
	Air dryer	malfunction.	component manufacturer speciﬁcations.
	Air dryer		Replace if defective.
	safety valve		Replace if defective.
		(c) Air dryer maintenance not	See Maintenance Schedule and Usage
		performed.	Guidelines (Table A, column 3, on page
			17).
		(d) Air dryer malfunction.	Verify operation of air dryer. Follow vehicle
			O.E. maintenance recommendations and
			O.E. maintenance recommendations and
			component Service Data information.
		(e) Improper governor control line	Go to Test 5 on page 29.
		installation to the reservoir.

	Technician removes	(f) Governor malfunction.	Go to Test 4 on page 29.
governor.		(f) Governor malfunction.	Go to Test 4 on page 29.
governor.

13.0 Reservoir		(a) Reservoir safety valve	Verify relief pressure is at vehicle or
safety valve		malfunction.	component manufacturer's speciﬁcations
releases air			(typically 150 psi). Replace if defective.
		(b) Governor malfunction.	Go to Test 4 on page 29.
		(c) Compressor unloader mechanism	Go to Test 6 on page 29.
		malfunction.

14.0 Air dryer		(a) Air dryer malfunction.	Verify operation of air dryer. Follow vehicle
doesn’t purge.			O.E. maintenance recommendations.
(Never hear		(b) Governor malfunction.	Go to Test 4 on page 29.
exhaust from air		(b) Governor malfunction.	Go to Test 4 on page 29.
dryer.)		(c) Air brake system leakage.	Go to Test 2 on page 28.
		(c) Air brake system leakage.	Go to Test 2 on page 28.
		(d) Improper governor control line	Go to Test 5 on page 29.
		installation to the reservoir.

15.0 Compressor constantly cycles (compressor remains unloaded for a very short time.)

(a)Air brake charging system maintenance not performed.

(b)Compressor unloader mechanism malfunction.

(c)Air dryer purge valve or delivery check valve malfunction.

Available reservoir capacity may be reduced by build-up of water etc. Drain and perform routine maintenance per Table A, columns 3 & 4, on page 17.

Go to Test 6 on page 29.

Verify operation of air dryer. Follow vehicle O.E. maintenance recommendations and component Service Data information.

(d) Air brake system leakage.

Go to Test 2 on page 28.

Symptom:	What it may indicate:	What you should do:

16.0 Compressor leaks air

Testing for leaks with soap solution.

(a)Compressor leaks air at connections or ports.

(b)Compressor unloader mechanism malfunction.

(c)Damaged compressor head gasket(s).

Head gasket locations

Check for leaking, damaged or defective compressor ﬁttings, gaskets, etc. Repair or replace as necessary.

Go to Test 6 on page 29.

An air leak at the head gasket(s) may indicate a downstream restriction such as a freeze-up or carbon blockage and/or could indicate a defective or missing safety valve. Find blockage (go to 9.0(f) for details) and then replace the compressor. Do not reuse the safety valve without testing. See Symptom 12.0(a).

17.0 Compressor	(a) Improperly installed plugs or coolant
leaks coolant	line ﬁttings.

Inspect for loose or over-torqued ﬁttings. Reseal and tighten loose ﬁttings and plugs as necessary. If overtorqued ﬁttings and plugs have cracked ports in the head, replace the compressor.

(b) Damaged compressor head	An air leak at the head gasket may indicate
gasket.	a downstream restriction such as a freeze-
	up or carbon blockage and/or could indicate
	a defective or missing safety valve. Find
	blockage (go to 9.0(f) for details) and then
	replace the compressor. Do not re-use the
	safety valve without testing. See Symptom
	12.0(a).

If casting porosity is detected, replace the compressor.

18.0 Noisy	(a) Damaged compressor.	Replace the compressor.
compressor
(Multi-cylinder
compressors only)

Other Miscellaneous Areas to Consider

This guide attempts to cover most compressor system problems. Here are some rare sources of problems not covered in this guide:

• Turbocharger leakage. Lubricating oil from leaking turbocharger seals can enter the air compressor intake and give misleading symptoms.

• Where a compressor does not have a safety valve installed, if a partial or complete discharge line blockage has occurred, damage can occur to the connecting rod bearings. Damage of this kind may not be detected and could lead to compressor problems at a later date.

Tests

Test 1: Excessive Oil Leakage at the

Head Gasket

Exterior leaks at the head gasket are not a sign that oil is being passed into the air charging system. Oil weepage at the head gasket does not prevent the compressor from building air.

Observe the amount of weepage from the head gasket.

If the oil is only around the cylinder head area, it is acceptable (return the vehicle to service), but, if the oil weepage extends down to the nameplate area of the compressor, the gasket can be replaced.

Look

for

Weepage

Test 2: Air Brake System and Accessory Leakage

Inspect for air leaks when working on a vehicle and repair them promptly.

Park the vehicle on level ground and chock wheels. Build system pressure to governor cut-out and allow the pressure to stabilize for one minute.

Step 1: Observe the dash gauges for two additional minutes without the service brakes applied.

Step 2: Apply the service brakes and allow the pressure to stabilize. Continue holding for two minutes (you may use a block of wood to hold the

pedal in position.) Observe the dash gauges.

If you see any noticeable decrease of the dash air gauge readings (i.e. more than 4 psi, plus two psi for each additional trailer) during either two minute test, repair the leaks and repeat this test to conﬁrm that they have been repaired.

Air leaks can also be found in the charging system, parking brakes, and/or other components - inspect and repair as necessary.

Test 3: Air Compressor Discharge

Temperature and Air Dryer Inlet		(* Note that only vehicles that have passed Test 2
	Temperature*	would be candidates for this test.)
Caution: The temperatures used in this test		4.	Then, while maintaining max rpm and
are not normal vehicle conditions.			pressure range, measure and record the
Above normal temperatures can cause oil (as			surface temperature of the ﬁttings:
vapor) to pass through the air dryer into the				at the compressor discharge port. (T1).
air brake system.				at the air dryer inlet ﬁtting. (T2).
This test is run with the engine at normal operating			Use a touch probe thermocouple for measuring
temperature, with engine at max. rpm. If			the temperature.
available, a dyno may be used.		5.	See table below.
1. Allow the compressor to build the air system		6.	Re test before returning the vehicle to
pressure to governor cut-in.			service.
2. Pump the brakes to bring the dash gauge
2. Pump the brakes to bring the dash gauge		T1		T2
pressure to 90 psi.		T1		T2
3. Allow the compressor to build pressure from		Compressor		Air Dryer	Action
3. Allow the compressor to build pressure from		Discharge		Inlet	Action
95 to 105 psi gauge pressure and maintain		Fitting		Fitting
this pressure range by cycling the brakes for		under		under	Temperatures are within
ﬁve (5) minutes.		under		under	Temperatures are within
ﬁve (5) minutes.		360°F		200°F	normal range for this test, check
	T1				other symptoms. Go to 4.0 (h).

		under		over	This could indicate a discharge


		360°F		200°F	line problem (e.g. restriction).
	T2				Call 1-800-AIR-BRAKE
	T2				(1-800-247-2725)
					and speak with our Tech Team.

		over		__	Compressor is running hot.
		360°F			Check coolant 4(f) and/or
	Discharge Line				discharge line 4(g).
	Discharge Line				discharge line 4(g).

Tests (continued)

Test 4: Governor Malfunction

1.Inspect control lines to and from the governor for restrictions (e.g. collapsed or kinked). Repair as necessary.

2.Using a calibrated external gauge in the

supply reservoir, service reservoir, or reservoir port of the D-2™ governor, verify cut-in and cut-out pressures are within vehicle OEM speciﬁcation.

3. If the governor is malfunctioning, replace it.

Test 5: Governor Control Line

1.Ensure that the governor control line from the reservoir is located at or near the top of the reservoir. (This line, if located near the bottom of the reservoir, can become blocked or restricted by the reservoir contents e.g. water or ice.)

2.Perform proper reservoir drain intervals and air dryer cartridge maintenance per Maintenance Schedule and Usage Guidelines (Table A on page 17).

3.Return the vehicle to service.

Test 6: Compressor Unloader Leakage

Bendix® Compressors: Park vehicle, chock wheels, and follow all standard safety procedures. Remove the governor and install a ﬁtting to the unloader port. Add a section of air hose (min 1 ft long for a 1/2" diameter line) and a gauge to the ﬁtting followed by a shut-off valve and an air source (shop air or small air tank). Open the

shut-off and charge the unloader port by allowing air pressure to enter the hose and unload the compressor. Shut off the air supply and observe the gauge. A steady reading indicates no leakage at the unloader port, but a falling reading shows that the unloader mechanism is leaking and needs to be serviced.

Appendix A: Information about the BASIC™ Test Kit (Bendix P/N 5013711)

Service writer records info - including
Service writer records info - including		days
the number of days since all air tanks		days
the number of days since all air tanks
were drained - and fills out symptom
were drained - and fills out symptom
checklist. Technician inspects items.
checklist. Technician inspects items.

START BASIC TEST

Park vehicle on LEVEL ground.

Chock wheels, drain air from system.

Drain contents of ALL air

tanks into BASIC™ cup

	Is there	YES
	less than one	YES
	less than one
	unit of liquid?

Bendix® Air System Inspection Cup

(BASIC™) Test Information

Vehicle OK.

Return vehicle to END TEST service.

Is
there more		Cloudy emulsion mixture
than one unit of:	YES	Cloudy emulsion mixture
than one unit of:	YES
• water, or
• cloudy emulsion
mixture?

YES, this is a high air use

vehicle.

NO, only oil.

Is this a transit vehicle, bulk unloader, or has more

than 5 axles?

NO, this is a low air			Is this vehicle
NO, this is a low air			being re-tested? (after	NO
	use vehicle.	YES	being re-tested? (after
	use vehicle.	YES	water, etc. was found
			water, etc. was found
			last time?)

			Find the point on the label
		where the number of oil units
High			meets the number of days*
High		since the vehicle's air tanks
		since the vehicle's air tanks
			were last drained.
				High
			Is the
			point above
		the HIGH Air Use		NO
			line on the	NO
			line on the
			cup?
	High		YES
			YES
Test for air			Use Test 2:
	leakage		Use Test 2:
	leakage		Air Leakage
			Air Leakage

	Find the point on the label
	where the number of oil units	Go to the
	meets the number of days*	Go to the	Change air dryer
	meets the number of days*	Advanced	Change air dryer
Low	since the vehicle's air tanks	Advanced		cartridge**
	since the vehicle's air tanks	Troubleshooting		cartridge**
	were last drained.	Troubleshooting
	were last drained.	Guide to find
		Guide to find
		reason(s) for
		presence of water	Test for air		Use Test 2:
	Is the		Test for air
	Is the		leakage
	point above		leakage		Air Leakage
	point above				Air Leakage
	the LOW Air Use	END TEST
	line on the
	cup?	Low
		Low
	NO				Re-test with the
Low					BASIC™ Test after
	YES				30 days***
					30 days***
					END TEST
	Vehicle OK.
	Return vehicle to	END TEST
	service.

Does	YES	Repair leaks and
	YES
the vehicle have
the vehicle have		return vehicle to		END TEST
excessive air		return vehicle to		END TEST
excessive air			service
leakage?			service
leakage?
NO
	NO (did not know
Was	when last		Re-test with the
the number of	drained)		Re-test with the
the number of	drained)		BASIC™ Test after
days since last			BASIC™ Test after	END TEST
draining			30 days***
known?

YES, number of days was known (30 - 90 days)

Replace the Compressor. If under warranty, follow standard procedures.

If, after a compressor was already replaced, the vehicle fails the Compressor BASIC™ test again, do not replace the compressor**** - use the

Advanced Troubleshooting Guide to investigate the cause(s).

END TEST

*If the number of days since the air tanks were drained is unknown

- use the 30 day line.

**Note: Typical air dryer cartridge replacement schedule is every

3 yrs/ 300K miles for low air use vehicles and every year/100K miles for high air use vehicles.

***To get an accurate reading for the amount of oil collected during a 30 day period, ask the customer not to drain the air tanks before returning. (Note that 30-90 days is the recommended air tank drain schedule for vehicles equipped with a Bendix air dryer that is properly maintained.) If, in cold weather conditions, the 30 day air tank drain schedule is longer than the customer's usual draining interval, the customer must determine, based on their experience with the vehicle, whether to participate now, or wait for warmer weather. See the cold weather tips in Bulletins TCH-008-21 and

TCH-008-22 (included on pages 33-35 of this document).

****Note: After replacing a compressor, residual oil may take a considerable period of time to be ﬂushed from the air brake system.

Appendix A continued: Information about the BASIC™Test Kit (Bendix P/N 5013711)

Filling in the Checklist for the Bendix® Air System Inspection Cup (BASIC™) Test

Note: Follow all standard safety precautions. For vehicles using a desiccant air dryer.

The Service Writer ﬁlls out these ﬁelds with information gained from the customer

Number of Days Since Air Tanks Were Last Drained: ________ Date: ___________Vehicle #: ____________

Engine SN __________________________ Vehicle Used for: _______________Typical Load:________ (lbs.) No. of Axles: ____ (tractor) ____ (trailer) No. of Lift Axles: ____ Technician’s Name: ____________________

The Service Writer also checks off any complaints that the customer makes to help the Technician in investigating.

Customer’s		Checklist for Technician
Customer’s			Have you conﬁrmed
complaint?
(Please check all that apply)
“Relay valve	leaks oil /	malfunctions”	no	yes*
“Dash valve	leaks oil /	malfunctions”	no	yes*
“Air dryer leaks oil”			no	yes*
“Governor malfunction”			no	yes*
“Oil in gladhands”			no	yes*

how much oil did you ﬁnd? ________________________________

“Oil on ground or vehicle exterior” no yes* amount described: ______________________________________

“Short air dryer cartridge life”

replaces every: ______________ miles, kms, or months “Oil in air tanks” amount described:_______________________

We will measure amount currently found when we get to step B of the test.

“Excessive engine oil loss” amount described: ______________

Is the engine leaking oil?	no	yes*
Is the compressor leaking oil?	no	yes*

Other complaint: _____________________________________

No customer complaint.

The Technician checks boxes for any of the complaints that

can be conﬁrmed.

* Note: A conﬁrmed complaint above does NOT mean that the compressor must be replaced.

The full BASIC™ test below will investigate the facts.

BASIC™ test starts here: STEP A - Select one:

This is a low air use vehicle: Line haul (single trailer) with 5 or less axles, or This is a high air use vehicle: Garbage truck, transit bus, bulk unloader, or line haul with more than 5 axles. Then go to Step B.

STEP B - Measure the Charging System Contents

1.Park and chock vehicle on level ground. Drain the air system by pumping the service brakes.

2.Completely drain ALL the air tanks into a single BASIC™cup.

3.If there is less than one unit of contents total, end the test now and return the vehicle to service. Vehicle passes.

4.If more than one oil unit of water (or a cloudy emulsion mixture)

	is found:
	(a) Change the vehicle’s air dryer cartridge	Oil
	- see Footnote 1,	Oil
	- see Footnote 1,	Units
	(b) Conduct the 4 minute leakage test (Step D),	Units
	(b) Conduct the 4 minute leakage test (Step D),

(c)STOP the inspection, and check the vehicle again after 30 days - see Footnote 2. STOP

+CK.

Otherwise, go to Step C.

The Technician selects the air use category for the vehicle. This decides which of the two acceptance lines on the cup will be used for the test below.

For an accurate test, the contents of all the air tanks on the vehicle should be used.

Note for returning vehicles that are being re tested after a water/cloudy emulsion mixture was found last time and the air dryer cartridge replaced: If more than one oil unit of water or a cloudy emulsion mixture is found again, stop the BASIC™ test and consult the air dryer's Service Data sheet troubleshooting section.

Footnote 1: Note: Typical air dryer cartridge replacement schedule is every 3 yrs/ 300K miles for low air use vehicles and every year/100K miles for high air use vehicles.

Footnote 2: To get an accurate reading for the amount of oil collected during a 30 day period, ask the customer not to drain the air tanks before returning. (Note that 30-90 days is the recommended air tank drain schedule for vehicles equipped with a Bendix air dryer that are properly maintained.) If, in cold weather conditions, the 30 day air tank drain schedule is longer than the customer's usual draining interval, the customer must determine, based on its experience with the vehicle, whether to participate now, or wait for warmer weather. See the cold weather tips in Bulletins TCH-008-21 and TCH-008-22 (included in Appendix B of the advanced troubleshooting guide).

Appendix A continued: Information about the BASIC™Test Kit (Bendix P/N 5013711)

Filling in the Checklist for the Bendix® Air System Inspection Cup (BASIC™) Test

Note: Follow all standard safety precautions. For vehicles using a desiccant air dryer.

STEP C - How to Use the BASIC™ Test

The Technician uses the chart (label) on the BASIC™ test cup to help decide the action to take, based on the amount of oil found. Use the lower acceptance line for low air use vehicles, and upper line for high air use vehicles (from Step A).

1. Record days since air		2. Record amount	3. Action to
tanks were last drained.		of oil found:	3. Action to
_________ days		_________ units	take
_________ days		_________ units
If number of days is:		if oil level is at or below	System OK.		STOP
If number of days is:		if oil level is at or below	System OK.		STOP
30-60 days (high air	acceptance line for number		Return to service.		TEST
use) or		of days	Return to service.
30-90 days (low air		if oil level is above	Go to Step D
use)	acceptance line for number		Go to Step D
		of days
Otherwise . . .		if oil level is at or below	System OK.		STOP
Otherwise . . .	30-day acceptance line		Return to service.TEST
(if the number of days is	if oil level is above 30-day		Stop inspection.
unknown, or outside the	if oil level is above 30-day		Test again	STOP
limits above)		acceptance line	after 30 days.	+ CK.
			See Footnote 2.

BASIC™ Test Example		Acceptance
BASIC™ Test Example		Lines	Oil
An oil level of 4 units in a sixty-day period is within the			Oil
acceptance area (at or below the line) for both low and			Level
high air use vehicles. Return the vehicle to service.		X
		X
The Technician looks for the point where the number
of days since the air tanks were drained meets the oil
level. If it is at or below the (low or high use) acceptance	Sixty days since last air	Decision point
line, the vehicle has passed the test. If the point is	tank draining

	above the line then go to the leakage test.	Air leakage is the number one
		Air leakage is the number one
		cause of compressors having
	STEP D - Air Brake System Leakage Test	to pump excessive amounts of
	STEP D - Air Brake System Leakage Test	air, in turn run too hot and pass
	Park the vehicle on level ground and chock wheels. Build system pressure to governor cut-out	oil vapor along into the system.
	and allow the pressure to stabilize for one minute.	Here the Technician conducts a
	1: Observe the dash gauges for two additional minutes without the service brakes applied.	four-minute test to see if leakage
	2: Apply service brakes for two minutes (allow pressure to stabilize) and observe the dash	is a problem with the vehicle
	gauges.	is a problem with the vehicle
	gauges.	being tested.
	If you see any noticeable decrease of the dash air gauge readings, repair leaks. Repeat	being tested.

	this test to conﬁrm that air leaks have been repaired and return vehicle to service. Please
	repeat BASIC™ test at next service interval. Note: Air leaks can also be found in the charging
	system, parking brakes, and/or other components - inspect and repair as necessary.

If no air leakage was detected, and if you are conducting this test after completing Step C, go to Step E.

STEP E - If no air leakage was detected in Step D

Replace the compressor.

Note: If the compressor is within warranty period, please follow standard warranty procedures. Attach the completed checklist to warranty claim.

The Technician only reaches Step E if the amount of oil found, or the amount of time since the air tanks were last drained exceeds the acceptance level, AND the vehicle passes the four-minute leakage test (no noticeable leakage was detected).

Appendix B

Technical Bulletin

Bulletin No.: TCH-008-021	Effective Date: 11/1/92
Page: 1 of 2

Subject: Air Brake System - Cold Weather Operation Tips

As the cold weather approaches, operators and ﬂeets alike begin to look to their vehicles with an eye toward “winterization”, and particularly what can be done to guard against air system freeze-up. Here are some BASIC™“Tips” for operation in the cold weather.

Engine Idling

Avoid idling the engine for long periods of time! In addition to the fact that most engine manufacturers warn that long idle times are detrimental to engine life, winter idling is a big factor in compressor discharge line freeze-up. Discharge line freeze-ups account for a signiﬁcant number of compressor failures each year. The discharge line recommendations under “Discharge Lines” are important for all vehicles but are especially so when some periods of extended engine idling can not be avoided.

Discharge Lines

The discharge line should slope downward from the compressor discharge port without forming water traps, kinks, or restrictions. Cross-overs from one side of the frame rail to the other, if required, should occur as close as possible to the compressor. Fitting extensions must be avoided. Recommended discharge line lengths and inside diameters are dependent on the vehicle application and are as follows.

Typical P&D, School Bus and Line Haul

The maximum discharge line length is 16 feet.

Length	I.D. Min.	Other Requirements
6.0-9.5 ft.	½ in.	None
9.5-12 ft.½ in.	Last 3 feet, including ﬁtting at the end of the
	discharge line, must be insulated with ½ inch thick closed
	cell polyethylene pipe insulation.
12-16 ft.	5/8 in.	Last 3 feet, including ﬁtting at the end of the
		discharge line, must be insulated with ½ inch thick
		closed cell polyethylene pipe insulation.

If the discharge line length must be less than 6 feet or greater than 16 feet, contact your local Bendix representative.

	Appendix B: Continued
Bulletin No.: TCH-008-021	Effective Date: 11/1/92
Page: 2 of 2

High Duty Cycle Vehicles (City Transit Coaches, Refuse Haulers, Etc.)

The maximum discharge line length is 16 feet.

Length		I.D. min.	Other Requirements
10-16 ft. ½ in.		None

If the discharge line length must be less than 10 feet or greater than 16 feet, contact your local Bendix representative.

System Leakage

Check the air brake system for excessive air leakage using the Bendix “Dual System Air Brake Test and Check List” (BW1279). Excessive system leakage causes the compressor to “pump” more air and also more moisture into the brake system.

Reservoir Draining (System Without Air Dryer)

Routine reservoir draining is the most BASIC™step (although not completely effective) in reducing the possibility of freeze-up. All reservoirs in a brake system can accumulate water and other contamination and must be drained! The best practice is to drain all reservoirs daily. When draining reservoirs; turn the ENGINE OFF and drain ALLAIR from the reservoir, better still, open the drain cocks on all reservoirs and leave them open over night to assure all contamination is drained (reference Service Data Sheet SD-04-400 for Bendix Reservoirs). If automatic drain valves are installed, check their operation before the weather turns cold (reference Service Data Sheet SD-03-2501 for Bendix® DV-2™ Automatic Drain Valves). It should be noted that, while the need for daily reservoir draining is eliminated through the use of an automatic drain valve, periodic manual draining is still required.

Alcohol Evaporator or Injector Systems

Check for proper operation of these systems by monitoring alcohol consumption for a few days (Reference Service Data Sheet SD-08-2301 for the Bendix Alcohol Evaporator). Too little means the system is not receiving adequate protection and too much simply wastes alcohol. As a general guide, these systems should consume approximately 1 to 2 ounces of alcohol per hour of compressor loaded time (compressing air). City pick-up and delivery vehicles will operate with the compressors loaded (compressing air) more while compressors on highway vehicles will be loaded less. These ﬁgures are approximate and assume that air system leakage is within the limits of the Bendix “Dual System Air Brake Test and Check List” (BW1279). Last but not least, begin using alcohol several weeks prior to freezing weather to ensure that the system is completely protected. Use only methanol alcohol, such as Bendix “Air Guard”, in evaporators or injectors.

Air Dryers

Make certain air brake system leakage is within the limits stated in BW1279. Check the operation and function of the air dryer using the appropriate Service Data Sheet for the air dryer.

AD-9™ Air Dryer . . . . . . . . . . . . . . . . . . . . . . . . . . . .Service Data Sheet SD-08-2412 AD-4™ Air Dryer . . . . . . . . . . . . . . . . . . . . . . . . . . . .Service Data Sheet SD-08-2407 AD-2™ Air Dryer . . . . . . . . . . . . . . . . . . . . . . . . . . . .Service Data Sheet SD-08-2403 AD-IP™ Air Dryer. . . . . . . . . . . . . . . . . . . . . . . . . . . .Service Data Sheet SD-08-2414 AD-SP™ Air Dryer . . . . . . . . . . . . . . . . . . . . . . . . . . .Service Data Sheet SD-08-2415 Trailer System-Guard® Air Dryer. . . . . . . . . . . . . . . .Service Data Sheet SD-08-2416 Bendix® PuraGuard QC™ Oil Coalescing Filter. . . . .Service Data Sheet SD-08-187B

Appendix B: Continued

Technical Bulletin

Bulletin No.: TCH-008-022	Effective Date: 1/1/1994
Page: 1 of 1

Subject: Additional Cold Weather Operation Tips for the Air Brake System

Last year we published Bulletin PRO-08-21 which provided some guidelines for “winterizing” a vehicle air brake system. Here are some additional suggestions for making cold weather vehicle operation just a little more bearable.

Thawing Frozen Air Lines

The old saying; “Prevention is the best medicine” truly applies here! Each year this activity accounts for an untold amount of unnecessary labor and component replacement. Here are some Do’s and Don’ts for prevention and thawing.

Do’s

1.Do maintain freeze prevention devices to prevent road calls. Don’t let evaporators or injectors run out of methanol alcohol or protection will be degraded. Check the air dryer for proper operation and change the desiccant when needed.

2.Do thaw out frozen air lines and valves by placing the vehicle in a warmed building. This is the only method for thawing that will not cause damage to the air system or its components.

3.Do use dummy hose couplings on the tractor and trailer.

4.Do check for sections of air line that could form water traps. Look for “drooping” lines.

Don’ts

1.Do not apply an open ﬂame to air lines and valves. Beyond causing damage to the internal nonmetallic parts of valves and melting or burning non-metallic air lines. WARNING: THIS

PRACTICE IS UNSAFE AND CAN RESULT IN VEHICLE FIRE!

2.Do not introduce (pour) ﬂuids into air brake lines or hose couplings (“glad hands”). Some ﬂuids used can cause immediate and severe damage to rubber components. Even methanol alcohol, which is used in Alcohol Evaporators and Injectors, should not be poured into air lines. Fluids poured into the system wash lubricants out of valves, collect in brake chambers and valves and can cause malfunction. Loss of lubricant can affect valve operating characteristics, accelerate wear and cause premature replacement.

3.Do not park a vehicle outside after thawing its air system indoors. Condensation will form in the system and freeze again. Place the vehicle in operation when it is removed to the outdoors.

Supporting Air and Electrical Lines

Make certain tie wraps are replaced and support brackets are re-assembled if removed during routine maintenance. These items prevent the weight of ice and snow accumulations from breaking or disconnecting air lines and wires.

Automatic Drain Valves (System without Air Dryer)

As we stated last year, routine reservoir draining is the most BASIC™step (although not completely effective) in reducing the possibility of freeze-up. While automatic drain valves relieve the operator of draining reservoirs on a daily basis, these valves MUST be routinely checked for proper operation. Don’t overlook them until they fail and a road call is required.

Bendix BA-921 Service Manual

Specifications and Main Features

Frequently Asked Questions

User Manual