UENR6748

October 2016

UENR6748 VOL 1 of 2
(Dimensions: 56 inches x 35 inches)
773E Off-Highway Truck
Air System
Serial #:
PRB1-UP
DJS1-UP

42 Page,
Volume 1 of 2: Standard Truck

FLUID POWER SYMBOLS

BASIC COMPONENT SYMBOLS

MAIN AUX

PUMP OR MOTOR FLUID CONDITIONER SPRING CONTROL VALVES RESTRICTION LINE RESTRICTION PUMP PUMP
(FIXED) (2 - SECTION) (VARIABLE & PRESSURE
COMPENSATED)

VARIABILITY SPRING LINE RESTRICTION PRESSURE HYDRAULIC PNEUMATIC LINE RESTRICTION ATTACHMENT
(ADJUSTABLE) (VARIABLE) COMPENSATION ENERGY TRIANGLES (VARIABLE & PRESSURE
COMPENSATED)

VALVE ENVELOPES VALVES VALVE PORTS

ONE POSITION TWO POSITION THREE POSITION TWO - WAY THREE - WAY FOUR - WAY

CONTROL VALVES CHECK VALVES

AB A B

P T P T
BASIC SPRING SHUTTLE PILOT
NORMAL POSITION SHIFTED POSITION INFINITE POSITION
SYMBOL LOADED CONTROLLED

FLUID STORAGE RESERVOIRS

VENTED PRESSURIZED RETURN ABOVE FLUID LEVEL RETURN BELOW FLUID LEVEL

MEASUREMENT ROTATING SHAFTS

PRESSURE TEMPERATURE FLOW UNIDIRECTIONAL BIDIRECTIONAL

COMBINATION CONTROLS

SOLENOID SOLENOID SOLENOID SOLENOID & SERVO THERMAL DETENT

OR MANUAL & PILOT PILOT OR MANUAL

MANUAL CONTROL SYMBOLS

PUSH - PULL LEVER MANUAL SHUTOFF GENERAL MANUAL PUSH BUTTON PEDAL SPRING

RELEASED PRESSURE PILOT CONTROL SYMBOLS REMOTE SUPPLY PRESSURE

EXTERNAL RETURN INTERNAL RETURN SIMPLIFIED COMPLETE INTERNAL

SUPPLY PRESSURE

ACCUMULATORS CROSSING & JOINING LINES HYDRAULIC & PNEUMATIC CYLINDERS

SPRING LOADED GAS CHARGED LINES CROSSING LINES JOINING SINGLE ACTING DOUBLE ACTING

HYDRAULIC PUMPS HYDRAULIC MOTORS INTERNAL PASSAGEWAYS

FIXED VARIABLE DISPLACEMENT FIXED VARIABLE DISPLACEMENT INFINITE

DISPLACEMENT NON-COMPENSATED DISPLACEMENT NON-COMPENSATED POSITIONING 3 POSITION 2 POSITION

UNIDIRECTIONAL UNIDIRECTIONAL

FLOW IN ONE PARALLEL CROSS FLOW IN

BIDIRECTIONAL BIDIRECTIONAL DIRECTION FLOW FLOW EITHER
DIRECTION

©2016 Caterpillar CAT, CATERPILLAR, their respective logos, “Caterpillar Yellow”, and the POWER EDGE trade dress as well as
All Rights Reserved corporate and product identity used herein, are trademarks of Caterpillar and may not be used without permission.

ELECTRICAL SYMBOLS TABLE

HYDRAULIC SYMBOLS (ELECTRICAL)

G
M
TRANSDUCER TRANSDUCER GENERATOR ELECTRIC MOTOR
(FLUID) (GAS / AIR)

PRESSURE SWITCH PRESSURE SWITCH TEMPERATURE ELECTRICAL WIRE

(ADJUSTABLE) SWITCH

WIRE NUMBER IDENTIFICATION CODES

ELECTRICAL SCHEMATIC EXAMPLE HYDRAULIC SCHEMATIC EXAMPLE

CURRENT STANDARD CURRENT STANDARD

HARNESS IDENTIFICATION CODE THIS EXAMPLE

INDICATES WIRE 135 IN HARNESS “AG”
WIRE

CIRCUIT NUMBER
325-AG135 PK-14 IDENTIFICATION WIRE COLOR

CIRCUIT NUMBER WIRE WIRE GAUGE

IDENTIFICATION COLOR 325-PK

PREVIOUS STANDARD

WIRE WIRE COLOR

325-PK-14 B A

CIRCUIT NUMBER WIRE GAUGE (EXAMPLE VALVE)

IDENTIFICATION
 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1

3 4

J J
UENR6748 VOL 1 of 2

1
(Dimensions: 56 inches x 35 inches)

5
26

MAIN
1 6
RESERVOIR

29 AIR
SEAT
I I
2

25
42 Page,

7 19
22
12

27
H 8 1 2 H
X
20
3 Y
10

SEE HYDRAULIC SCHEMATIC

9 3
2

1
SECONDARY
3
2
RESERVOIR 21
10 3 1

12

24
G 1 4 2
1 2 G
2
2 1

3 11
10 30
X X
13
17 23

MASTER CYL (REAR)

18 12 Y Y MASTER CYL (FRONT) 13
SEE HYDRAULIC SCHEMATIC 12
28
F 11 F
2
31
GOV Y
1 AIR DRYER M N
J DBL CK VALVE
G
RELAY VALVE S
14 DBL CK (REAR) 33
VALVE
3
PRESS PROTECT
H
VALVE
U

RELAY VALVE

D
(FRONT) 30
16 AIR COMPRESSOR
9 10 RELAY VALVE
E (ARC)
NO MODEL PART NO. NAME DESCRIPTION
E 15 K
E
CUT-IN: 690 35 kPa R

1 4N-6842 COMPRESSOR GP CUT-OUT: 830 35 kPa

1 DISCHARGE PORT
H O 5
RATED FLOW: 12 SCFM AT 1250 RPM
CUT-IN: 646 kPa MIN C
2 4N-9680 GOVERNOR AS B ONE-WAY
CUT-OUT: 816 35 kPa CK VALVE
24 29
DESICCANT FILL W/PURGE+MUFFLER
3 3E-3535 DRYER AS F
RELIEF PRESSURE: 1380 kPa 8 AIR RESERVOIR
(SERVICE)
JCT PLATE
4 141-2607 VALVE-DRAIN DRAIN VALVE FOR AIR TANK
CAB ENCLOSURE
5 360-6826 RESERVOIR-AIR CAP 60L, EN286 & SAE J10 APPV'D 8 7 6 5 4 3 2 1 PRESS PROT
VALVE
MAX WORKING PRESS: 1034 kPa E SAFETY VALVE
BK AIR
D SECONDARY PRESS D
6 344-7389 SENSOR GP-PRES AIR PRESSURE SENSOR SENSOR
26 T
BRAKE "ON"
FRT BRAKE 19
7 128-4972 VALVE GP-AIR ON-OFF FRT BRK SWITCH W/DETENT FRONT BK
7
VALVE RATIO VALVE
8 8W-6908 VALVE-RATIO FRONT BRAKE RATIO VALVE
F N DRAIN
9 159-5149 VALVE-RELAY CRACKING PRESSURE: 1036 kPa NNP 6 VALVE
X
10 159-5149 VALVE-RELAY CRACKING PRESSURE: 1036 kPa NNP C 4
O
11 4K-9714 VALVE GP-CHECK SHUTTLE VALVE (DBL CHECK) SERV BRAKE
CONT VALVE
12 8X-6987 CYL GP-AIR HYD BORE 152.4mm STROKE 187.32mm
CONVERSION RATIO= 23:1 18
13 8W-3405 CYLINDER GP- BORE 171.6mm STROKE 256.3mm
J
AIR OVER HYD CONVERSION RATIO: 6.6:1 AIR
Z
14 3E-2034 SWITCH AS-PRES BRAKE SWITCH SEAT
ACTUATION PRESS: 80 kPa MAX ELIM
C B AA C
DEACTUATION PRESS: 55 20 kPa WITH REAR CAB WALL
ARC
15 166-7781 SWITCH AS-PRES STOPLAMP SWITCH K
BB
25
ACTUATION PRESS: 45 kPa MAX DBL CK
VALVE
DEACTUATION PRESS: 5 kPa MIN Y 14
SECONDARY & PARK
16 165-2136 VALVE AS-RETR DELIVERY PRESSURE: 34-544 kPa 17 BRAKE SW CONT VALVE
ELIMINATE WITH ARC
17 6D-3781 VALVE GP-CHK SHUTTLE VALVE (DBL CHECK) RETR SW
D
Q 4
18 247-1292 VALVE SERVICE BRAKE VALVE ELIM BK CONT VALVE DBL CK
WITH
ELIM WITH ARC
(RETR)
15 W
VALVE
19 2G-8815 VALVE-PROTECT PRESSURE PROTECTION VALVE ARC W
STOPLAMP DRAIN
OPEN PRESS: 550kPa - ASCEND SUP 28 VALVE
PARK BRAKE SW
CLOSE PRESS:485kPa -DESCEND DEL CONT VALVE
17
ELIM
20 162-7880 RESERVOIR CAP: 20L EN286 & SAE J10 APP'D T 16 23 A DD
B WITH D S
CAB ENCLOSURE B
MAX WORKING PRESS: 1050 kPa ARC R PARK BRAKE
FF
RESET VALVE
21 172-6232 VALVE GP INVERSION VALVE - NP 27
SEC BRAKE
DEL PRESS DESCENDS AT 1:1 WITH ARC CONT VALVE 34 INV KK
PRESS VALVE ONE-WAY
ASCENDING CONTROL PRESS SW EE DEL
S U CHECK
22 247-1293 VALVE GP-AIR SERVICE FOOT VALVE VALVE
32 G
CC
23 464-6945 VALVE GP-AIR PARK BRAKE SWITCH WITH DETENT INV VALVE CTRL
AIR
24 160-2445 SWITCH AS-PRES SECONDARY "BRAKE ON" SWITCH ARC
RESERVOIR
INVERSION
(SEC)
ACTUATION PRESS: 517 35 kPa S D VALVE
DEACTUATION PRESS: 448 35 kPa
17 INV VALVE
25 773,775 113-1543 VALVE GP-BRK HYDRAULIC / AIR VALVE AIR CIRCUIT COLOR DESCRIPTIONS
RETR SW
21 SUPPLY
AIR COMPRESSOR OUTPUT AND CIRCUITS 22 JJ
AIR EXHAUST/DRAIN
26 7D-6936 VALVE-CHECK ONE-WAY CHECK ON MAIN RESERVOIR ATTACHMENT CIRCUIT
A H A
27 6D-1432 VAVLE-CHECK ONE-WAY CHECK ON SEC RESERVOIR
28 20 THIS SCHEMATIC IS FOR THE 773E OFF-HIGHWAY TRUCK AIR SYSTEM
28 103-4977 SWITCH AS-PRES RETARDER SWITCH X VOLUME 1 of 2: STANDARD TRUCK
29 6B-9664 VALVE-SAFETY SAFETY VALVE, OPENS AT 1034 kPa MEDIA NUMBER: UENR6748
M SCHEMATIC PART NUMBER: 460-6701, CHANGE: 00, VERSION: -
30 213-1081 VALVE AS SUPPLY CUT OFF AND DELIVERY Components are shown installed on a fully operable machine with the key and engine on, transmission shifter
in neutral, front brakes switched off and with parking brake set.
EXHAUSTED AT 415 35 kPa Refer to the appropriate Service Manual for Troubleshooting, Specifications and Systems Operations.
Refer to the Parts Manual using a specific serial number prefix in SIS before ordering parts from this schematic.

16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1
 UENR6748
October 2016

UENR6748 VOL 2 of 2
(Dimensions: 56 inches x 35 inches)
773E Off-Highway Truck
Air System
Serial #:
PRB1-UP
DJS1-UP

42 Page,
Volume 2 of 2: ARC Equipped Truck

FLUID POWER SYMBOLS

BASIC COMPONENT SYMBOLS

MAIN AUX

PUMP OR MOTOR FLUID CONDITIONER SPRING CONTROL VALVES RESTRICTION LINE RESTRICTION PUMP PUMP
(FIXED) (2 - SECTION) (VARIABLE & PRESSURE
COMPENSATED)

VARIABILITY SPRING LINE RESTRICTION PRESSURE HYDRAULIC PNEUMATIC LINE RESTRICTION ATTACHMENT
(ADJUSTABLE) (VARIABLE) COMPENSATION ENERGY TRIANGLES (VARIABLE & PRESSURE
COMPENSATED)

VALVE ENVELOPES VALVES VALVE PORTS

ONE POSITION TWO POSITION THREE POSITION TWO - WAY THREE - WAY FOUR - WAY

CONTROL VALVES CHECK VALVES

AB A B

P T P T
BASIC SPRING SHUTTLE PILOT
NORMAL POSITION SHIFTED POSITION INFINITE POSITION
SYMBOL LOADED CONTROLLED

FLUID STORAGE RESERVOIRS

VENTED PRESSURIZED RETURN ABOVE FLUID LEVEL RETURN BELOW FLUID LEVEL

MEASUREMENT ROTATING SHAFTS

PRESSURE TEMPERATURE FLOW UNIDIRECTIONAL BIDIRECTIONAL

COMBINATION CONTROLS

SOLENOID SOLENOID SOLENOID SOLENOID & SERVO THERMAL DETENT

OR MANUAL & PILOT PILOT OR MANUAL

MANUAL CONTROL SYMBOLS

PUSH - PULL LEVER MANUAL SHUTOFF GENERAL MANUAL PUSH BUTTON PEDAL SPRING

RELEASED PRESSURE PILOT CONTROL SYMBOLS REMOTE SUPPLY PRESSURE

EXTERNAL RETURN INTERNAL RETURN SIMPLIFIED COMPLETE INTERNAL

SUPPLY PRESSURE

ACCUMULATORS CROSSING & JOINING LINES HYDRAULIC & PNEUMATIC CYLINDERS

SPRING LOADED GAS CHARGED LINES CROSSING LINES JOINING SINGLE ACTING DOUBLE ACTING

HYDRAULIC PUMPS HYDRAULIC MOTORS INTERNAL PASSAGEWAYS

FIXED VARIABLE DISPLACEMENT FIXED VARIABLE DISPLACEMENT INFINITE

DISPLACEMENT NON-COMPENSATED DISPLACEMENT NON-COMPENSATED POSITIONING 3 POSITION 2 POSITION

UNIDIRECTIONAL UNIDIRECTIONAL

FLOW IN ONE PARALLEL CROSS FLOW IN

BIDIRECTIONAL BIDIRECTIONAL DIRECTION FLOW FLOW EITHER
DIRECTION

©2016 Caterpillar CAT, CATERPILLAR, their respective logos, “Caterpillar Yellow”, and the POWER EDGE trade dress as well as
All Rights Reserved corporate and product identity used herein, are trademarks of Caterpillar and may not be used without permission.

ELECTRICAL SYMBOLS TABLE

HYDRAULIC SYMBOLS (ELECTRICAL)

G
M
TRANSDUCER TRANSDUCER GENERATOR ELECTRIC MOTOR
(FLUID) (GAS / AIR)

PRESSURE SWITCH PRESSURE SWITCH TEMPERATURE ELECTRICAL WIRE

(ADJUSTABLE) SWITCH

WIRE NUMBER IDENTIFICATION CODES

ELECTRICAL SCHEMATIC EXAMPLE HYDRAULIC SCHEMATIC EXAMPLE

CURRENT STANDARD CURRENT STANDARD

HARNESS IDENTIFICATION CODE THIS EXAMPLE

INDICATES WIRE 135 IN HARNESS “AG”
WIRE

CIRCUIT NUMBER
325-AG135 PK-14 IDENTIFICATION WIRE COLOR

CIRCUIT NUMBER WIRE WIRE GAUGE

IDENTIFICATION COLOR 325-PK

PREVIOUS STANDARD

WIRE WIRE COLOR

325-PK-14 B A

CIRCUIT NUMBER WIRE GAUGE (EXAMPLE VALVE)

IDENTIFICATION
 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1

3 4

J 2 J
UENR6748 VOL 2 of 2

1
26
(Dimensions: 56 inches x 35 inches)

MAIN
1 6
RESERVOIR

29 AIR
SEAT
I I
2

25
42 Page,

7 3
19
2
22
12
1

27
H 1 2 H
8 33 X
20
3 Y
30
10

SEE HYDRAULIC SCHEMATIC

9 3
2

1
SECONDARY
3
RESERVOIR
3 1
21
2
10
1

12 31
24
G 1 4 2
1 2 G
2
2 1

10 11 30

X X
13
17 23

MASTER CYL (REAR)

18 12 Y Y MASTER CYL (FRONT) 13

SEE HYDRAULIC SCHEMATIC 12

F 11 F
2
31
GOV Y
1 AIR DRYER M N
12 12 J DBL CK VALVE
G
RELAY VALVE S
DBL CK
14 VALVE
(REAR) 33
3
3 3 17 H
PRESS PROTECT
1 2 VALVE
2 2 U

1 1 RELAY VALVE
10 10
D
(FRONT) 30
AIR COMPRESSOR
16 9 10 RELAY VALVE
E (ARC)

E E
32 17 15 K
R

H O 5
28
C
B ONE-WAY
CK VALVE
24 29
F
NO. MODEL PART NO. NAME DESCRIPTION 8 AIR RESERVOIR
(SERVICE)
1 4N-6842 COMPRESSOR GP CUT-IN: 690 35 kPa JCT PLATE
CUT-OUT: 830 35 kPa
1 DISCHARGE PORT CAB ENCLOSURE
8 7 6 5 4 3 2 1 PRESS PROT
RATED FLOW: 12 SCFM AT 1250 RPM
VALVE
2 4N-9680 GOVERNOR AS CUT-IN: 646 kPa MIN E SAFETY VALVE
BK AIR
D CUT-OUT: 816 35 kPa
SECONDARY PRESS D
3 3E-3535 DRYER AS DESICCANT FILL W/PURGE+MUFFLER SENSOR
26 T
BRAKE "ON"
RELIEF PRESSURE: 1380 kPa FRONT BK FRT BRAKE 19
VALVE 7 RATIO VALVE
4 141-2607 VALVE-DRAIN DRAIN VALVE FOR AIR TANK
5 360-6826 RESERVOIR-AIR CAP 60L, EN286 & SAE J10 APPV'D F N DRAIN
MAX WORKING PRESS: 1034 kPa 6 X
VALVE

6 344-7389 SENSOR GP-PRESSAIR PRESSURE SENSOR C 4

7 128-4972 VALVE GP-AIR ON-OFF FRT BRK SWITCH W/DETENT
O
8 8W-6908 VALVE-RATIO FRONT BRAKE RATIO VALVE SERV BRAKE
9 159-5149 VALVE-RELAY CRACKING PRESSURE: 1036 kPa NNP CONT VALVE
10 159-5149 VALVE-RELAY CRACKING PRESSURE: 1036 kPa NNP
11 4K-9714 VALVE GP-CHECK SHUTTLE VALVE (DBL CHECK)
18
12 8X-6987 CYL GP-AIR HYD BORE 152.4mm STROKE 187.32mm
CONVERSION RATIO= 23:1 J
13 8W-3405 CYLINDER GP- BORE 171.6mm STROKE 256.3mm AIR
Z
AIR OVER HYD CONVERSION RATIO: 6.6:1 SEAT
14 3E-2034 SWITCH AS-PRESS BRAKE SWITCH
ACTUATION PRESS: 80 kPa MAX ELIM
C B AA C
DEACTUATION PRESS: 55 20 kPa WITH REAR CAB WALL
15 166-7781 SWITCH AS-PRESS STOPLAMP SWITCH ARC
ACTUATION PRESS: 45 kPa MAX
K
BB
25
DEACTUATION PRESS: 5 kPa MIN DBL CK
VALVE
16 165-2136 VALVE AS-RETR DELIVERY PRESSURE: 34-544 kPa Y 14
17 6D-3781 VALVE GP-CHK SHUTTLE VALVE (DBL CHECK) SECONDARY & PARK
18 247-1292 VALVE SERVICE BRAKE VALVE 17 BRAKE SW CONT VALVE
19 2G-8815 VALVE-PROTECT PRESSURE PROTECTION VALVE
ELIMINATE WITH ARC
OPEN PRESS: 550kPa - ASCEND SUP RETR SW
D
Q 4
CLOSE PRESS:485kPa -DESCEND DEL ELIM DBL CK
BK CONT VALVE
WITH
ELIM WITH ARC
(RETR)
15 W
VALVE
20 162-7880 RESERVOIR CAP: 20L EN286 & SAE J10 APP'D ARC W
STOPLAMP DRAIN
MAX WORKING PRESS: 1050 kPa
172-6232 VALVE GP INVERSION VALVE - NP
28 PARK BRAKE SW VALVE
21
DEL PRESS DESCENDS AT 1:1 WITH CONT VALVE
ASCENDING CONTROL PRESS
17
22 247-1293 VALVE GP-AIR SERVICE FOOT VALVE ELIM
128-4971 VALVE GP-AIR PARK BRAKE SWITCH WITH DETENT T 16 23 A DD
B 23
WITH D S
CAB ENCLOSURE B
24 160-2445 SWITCH AS-PRESS SECONDARY "BRAKE ON" SWITCH
ARC R PARK BRAKE
ACTUATION PRESS: 517 35 kPa RESET VALVE FF
DEACTUATION PRESS: 448 35 kPa 27
SEC BRAKE
25 773,775 113-1543 VALVE GP-BRK HYDRAULIC / AIR VALVE ARC CONT VALVE 34 INV KK
PRESS VALVE ONE-WAY
26 7D-6936 VALVE-CHECK ONE-WAY CHECK ON MAIN RESERVOIR SW S EE DEL
U CHECK
27 6D-1432 VAVLE-CHECK ONE-WAY CHECK ON SEC RESERVOIR
VALVE
28 103-4977 SWITCH AS-PRESS RETARDER SWITCH 32 INV VALVE CTRL G
CC
AIR
RESERVOIR
ARC INVERSION
29 6B-9664 VALVE-SAFETY SAFETY VALVE, OPENS AT 1034 kPa (SEC)
S D VALVE
30 159-5149 VALVE-RELAY CRACKING PRESSURE: 1036 kPa NNP
31 147-6277 VALVE GP SHUTTLE VALVE (DBL CHECK)
32 127-4661 VALVE GP AUTO RETR CONTROL (ARC) VALVE
17 INV VALVE
RETR SW
21 SUPPLY
22 JJ
AIR CIRCUIT COLOR DESCRIPTIONS
A AIR COMPRESSOR OUTPUT AND CIRCUITS
AIR EXHAUST/DRAIN
H A
ATTACHMENT CIRCUIT 28 20 THIS SCHEMATIC IS FOR THE 773E OFF-HIGHWAY TRUCK AIR SYSTEM
33 153-9540 VALVE-PRESS DELIVERY OPENS AT 374 kPa
X VOLUME 2 of 2: ARC EQUIPPED TRUCK
PROTECTION DELIVERY CLOSES AT 306 kPa
34 213-1081 VALVE AS SUPPLY CUT OFF AND DELIVERY MEDIA NUMBER: UENR6748
EXHAUSTED AT 415 35 kPa
M SCHEMATIC PART NUMBER: 460-6701, CHANGE: 00, VERSION: -
Components are shown installed on a fully operable machine with the key and engine on, transmission shifter
in neutral, front brakes switched off and with parking brake set.
Refer to the appropriate Service Manual for Troubleshooting, Specifications and Systems Operations.
Refer to the Parts Manual using a specific serial number prefix in SIS before ordering parts from this schematic.

16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1