SD-11-550 Service Bulletin/Repair Instructions

SD-11-550

Bendix® BA-3800™ Single-Cylinder Compressor

1. INTRODUCTION

The function of the air compressor is to provide and maintain

air under pressure to operate devices in air brake systems.

The Bendix® BA-3800™ compressor is a naturally aspirated

single-cylinder reciprocating compressor with a rated

displacement of 20.0 cubic feet per minute at 1500 RPM.

The compressor consists of a water-cooled cylinder head

assembly and an integral water-cooled crankcase assembly.

The cylinder head assembly is made up of the cylinder head,

intermediate plate, and valve plate assembly and uses two

(2) sealing gaskets. Both the cylinder head and valve plate

are aluminum. The cylinder head contains air and water

ports, as well as an unloader assembly. The valve plate may

contain a water port. Both the cylinder head and valve plate

assist in cooling.
The BA-3800 compressor is equipped with a safety valve to

protect the compressor head, for example, in the event of

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 side of the cylinder head is etched with information

identifying the customer part number, Bendix part number,

and manufacturing date. See Figure 2.

Cylinder Head
Safety Valve
Intermediate

Plate
The valve plate assembly has 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.
Valve Plate

Assembly
The cast iron crankcase houses the piston assembly,

connecting rod, crankshaft, and related bearings. An end

cover encloses the internal components. The compressor

gear engages the engine drive gear.
Crankcase
Figure 1 – Bendix BA-3800 Compressor
Customer

Information

Manufacturing Data
Figure 2 – Cylinder Head Etching
Product

Data (Data

Matrix Code)
TABLE OF CONTENTS

GENERAL SAFETY GUIDELINES
WARNING! PLEASE READ AND

FOLLOW THESE INSTRUCTIONS

TO AVOID PERSONAL INJURY OR DEATH:
2
When working on or around a vehicle, the following

guidelines should be observed AT ALL TIMES:

▲Park the vehicle on a level surface, apply the parking

brakes and always block the wheels. Always wear personal

protection equipment.

▲Stop the engine and remove the 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.

▲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.

▲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 a Bendix® AD-IS® air dryer system, a Bendix®

DRM™ dryer reservoir module, a Bendix ® AD-9si ®, AD-HF®,

or AD-HFi ® air dryer, be sure to drain the purge reservoir.

▲Following the vehicle manufacturer’s recommended

procedures, deactivate the electrical system in a manner

that safely removes all electrical power from the vehicle.

▲Never exceed manufacturer’s recommended pressures.

▲Never connect or disconnect a hose or line containing

pressure; it may whip and/or cause hazardous airborne

dust and dirt particles. Wear eye protection. Slowly open

connections with care, and verify that no pressure is

present. Never remove a component or plug unless you are

certain all system pressure has been depleted.

▲Use only genuine Bendix ® brand replacement parts,

components and kits. Replacement hardware, tubing, hose,

fittings, wiring, etc. must be of equivalent size, type and

strength as original equipment and be designed specifically

for such applications and systems.

▲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.

▲Prior to returning the vehicle to service, make certain all

components and systems are restored to their proper

operating condition.

▲For vehicles with Automatic 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.

▲The power MUST be temporarily disconnected from the

radar sensor whenever any tests USING A DYNAMOMETER

are conducted on a vehicle equipped with a Bendix ®

Wingman ® system.

▲You should consult the vehicle manufacturer's operating

and service manuals, and any related literature, in

conjunction with the Guidelines above.
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

2. Operation  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

3. Preventive Maintenance . . . . . . . . . . . . . . . . . . 7

4. Service Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

5. Compressor Replacement  . . . . . . . . . . . . . . . 10

Technical Specifications  . . . . . . . . . . . . . . . . . . . . 14
Discharge Port
Coolant Ports
Alternate View
End Cover
Air Inlet Port

Safety Valve
Unloader Cover
Intermediate Plate

Unloader Piston
Valve Plate Assembly
Connecting Rod
Piston
Crankcase
Crankshaft

Crankcase Cover
Oil Drain Location
Figure 3 – Bendix BA-3800 Compressor Cutaway
3
2. 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.
Discharge Valve Closed

Air Inlet Port
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/

gasket to flex open. Atmospheric air flows through the open

inlet valve and fills the cylinder bore above the piston. See

Figure 4.
Unloader

Piston Down

and Seated
Valve

Plate
Inlet Valve

Open
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/gasket closes. Air above the piston is trapped by the

closed inlet reed valve/gasket 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. See Figure 5.
Piston Moving Down
Figure 4 – Operation: Loaded (Intake)

Discharge Valve Open

Air Discharge

Port
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.
Valve

Plate
Unloader

Piston Down

and Seated

Inlet Valve

Closed
Piston Moving Up
Figure 5 – Operation: Loaded (Compression)
4
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 piston to move

away from its seat on the valve plate assembly. When the

unloader piston is unseated, an air passageway is opened

between the cylinder bore and a secondary compartment, or

“closed room,” in the interior of 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 “closed room." The size

of the closed room is sufficient to accept the compressed air

provided by the compressor piston without creating excessive

air pressure in the closed room. On the piston down stroke

(TDC to BDC) air flows in the reverse direction, from the

“closed room” past the unseated unloader piston and inlet

reed valve/gasket, and into the cylinder bore as shown in

Figure 6.

NOTE: For optimum performance, it is recommended that

the air dryer is equipped with a “turbo cut-off” (discharge line

closed) feature.
Air from

Governor

Unloader Port
Closed Room
Unloader

Piston Up

and Seated
Air in compressor shuttles back and forth from

the cylinder to the closed room.
Figure 6 – Operation: Unloaded
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.

NOTE: There is no external oil supply line; the oil delivery is

located at the engine to compressor mounting face.

This pressurized oil flows to the front crankshaft journal

associated with the mounting flange, which, via an oil passage

in the crankshaft, routes pressurized oil to the connecting rod

bearings and the rear crankshaft journal. Spray lubrication

of the cylinder bore and connecting rod wrist pin bushing 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

the opening at the compressor mounting flange.
5
COOLING
AIR INDUCTION
The BA-3800 compressor is cooled by air flowing through

the engine compartment as it passes the compressor and

by the flow of engine coolant through the crankcase and

cylinder head.
The BA-3800 compressor is only permitted to be naturally

aspirated. The use of engine turbocharger as an air source

is not allowed. See Figure 8 for an example of a naturally

aspirated air induction system.
Coolant supplied by the engine cooling system passes

through connecting lines into the crankcase and passes

through internal passages in the valve plate assembly,

intermediate plate, and cylinder head and returns to the

engine.

Figure 7 illustrates the approved coolant flow connections.

Proper cooling is important in minimizing discharge air

temperatures - see the product specifications on page 14

for specific requirements.

Unloader Cover
Head Bolt (6)
Coolant

In or Out
Inlet Port
Discharge Port
Unloader Control

Port
CYLINDER HEAD PORT IDENTIFICATION

The cylinder head connection ports are identified

with cast-in numerals as follows:
Connection Port
Port Number
Inlet Port
0
Discharge Port
2
Coolant IN or OUT
9
Unloader Control Port
4
Figure 7 – BA-3800 Cylinder Head
6
Inlet
Discharge
Air Dryer
Engine Air

Intake
BA-3800

Compressor
Governor
Unloader
Supply Reservoir
Figure 8 – Compressor Charging System Example
3. PREVENTIVE MAINTENANCE
COMPRESSOR COOLING
Regularly scheduled maintenance is the single most

important factor in maintaining the air brake charging system.

Refer to BW1971, Advanced Troubleshooting Guide for Air

Brake Compressors, on B2Bendix.com for a guide to various

considerations that must be given to maintenance of the

compressor and other related charging system components.
To inspect compressor cooling, complete the following steps:
Review the Bendix® 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 BA-3800 compressor is designed for connection to the

vacuum side 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 the 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. If using a threaded compressor inlet fitting, verify that

the fitting is tight (check the torque).

12 3

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