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).