ONE POSITION TWO POSITION THREE POSITION
VENTED
PRESSURIZED
RETURN ABOVE FLUID LEVEL RETURN BELOW FLUID LEVEL
LINES CROSSING LINES JOINING
TWO - WAY THREE - WAY FOUR - WAY
SPRING CONTROL VALVES RESTRICTION LINE RESTRICTION
(FIXED)
PUMP
(2 - SECTION)
SPRING
(ADJUSTABLE)
VARIABILITY LINE RESTRICTION
(VARIABLE)
PRESSURE
COMPENSATION
PUMP
(VARIABLE & PRESSURE
COMPENSATED)
MEASUREMENT
PRESSURE TEMPERATURE FLOW
ROTATING SHAFTS
UNIDIRECTIONAL BIDIRECTIONAL
PUSH - PULL LEVER PEDALGENERAL MANUAL PUSH BUTTON SPRING
FIXED
DISPLACEMENT
VARIABLE DISPLACEMENT
NON-COMPENSATED
UNIDIRECTIONAL
BIDIRECTIONAL
VALVE ENVELOPES VALVE PORTS
FLUID CONDITIONERPUMP OR MOTOR
FLUID POWER SYMBOLS
UNIDIRECTIONAL
BIDIRECTIONAL
RELEASED PRESSURE
EXTERNAL RETURN INTERNAL RETURN
REMOTE SUPPLY PRESSURE
SIMPLIFIED
HYDRAULIC PUMPS
ACCUMULATORS
SPRING LOADED GAS CHARGED
SOLENOID
OR MANUAL
SOLENOID
& PILOT
SOLENOID &
PILOT OR MANUAL
SOLENOID SERVO THERMAL DETENT
HYDRAULIC & PNEUMATIC CYLINDERS
DOUBLE ACTINGSINGLE ACTING
BASIC
SYMBOL
SPRING
LOADED
CHECK VALVES
2 POSITION
INFINITE
POSITIONING
FLOW IN ONE
DIRECTION
FLOW IN
EITHER
DIRECTION
3 POSITION
CROSS
FLOW
PARALLEL
FLOW
INTERNAL PASSAGEWAYS
NORMAL POSITION
AB
PT
AB
PT
SHIFTED POSITION INFINITE POSITION
CONTROL VALVES
ATTACHMENT
MANUAL SHUTOFF
SHUTTLE PILOT
CONTROLLED
MAIN AUX
LINE RESTRICTION
(VARIABLE & PRESSURE
COMPENSATED)
MANUAL CONTROL SYMBOLS
HYDRAULIC MOTORS
FLUID STORAGE RESERVOIRS
CROSSING & JOINING LINES
VALVES
PILOT CONTROL SYMBOLS
COMBINATION CONTROLS
BASIC COMPONENT SYMBOLS
ENERGY TRIANGLES
HYDRAULIC PNEUMATIC
INTERNAL
SUPPLY PRESSURE
COMPLETE
FIXED
DISPLACEMENT
VARIABLE DISPLACEMENT
NON-COMPENSATED
HYDRAULIC SYMBOLS (ELECTRICAL)
ELECTRICAL SYMBOLS TABLE
325-AG135 PK-14
HARNESS IDENTIFICATION CODE THIS EXAMPLE
INDICATES WIRE 135 IN HARNESS “AG”
325-PK-14
WIRE GAUGE
WIRE COLOR
CIRCUIT NUMBER
IDENTIFICATION
WIRE NUMBER IDENTIFICATION CODES
CURRENT STANDARD
PREVIOUS STANDARD
ELECTRICAL SCHEMATIC EXAMPLE HYDRAULIC SCHEMATIC EXAMPLE
325-PK
WIRE COLOR
CIRCUIT NUMBER
IDENTIFICATION
B
WIRE
WIRE
(EXAMPLE VALVE)
CURRENT STANDARD
TRANSDUCER
(FLUID)
M
ELECTRIC MOTORTRANSDUCER
(GAS / AIR)
G
GENERATOR
PRESSURE SWITCH ELECTRICAL WIREPRESSURE SWITCH
(ADJUSTABLE)
TEMPERATURE
SWITCH
PRESSURE
SWITCH
TEMPERATURE
SWITCH
LEVEL
SWITCH
FLOW
SWITCH
ELECTRICAL SYMBOLS (ELECTRICAL)
A
CIRCUIT NUMBER
IDENTIFICATION
WIRE
COLOR
WIRE GAUGE
T
RENR8824-01
20 Page, (Dimensions: 39 inches x 24 inches)
RENR8824-01
October 2011
Hydraulic System
Printed in U.S.A.© 2011 Caterpillar, All Rights Reserved
990H Series II Wheel Loader Tier 3
BWX1-UP
DD
EE
CC
NN
JJ
KK
LL
MM
LL
MM
JJ
KK
NN
4
24
17b
1328 30
16 39
1617a22
23
1244 52 53
106
55 56
58
59
102 103
104
105
2 13142627
28
3133384551
56
29 30
5861
44 52 53 26
55 56
59 102 103 104
105 106
35 41 49
50 54 57 202
203
14 29 26
2731 33
2
38 51 56
58 61
19f18 19e17a
19e17b
17a9
19f18
12
4
5
5
25
25
15
20
34
60 37
43
42
340
46 47 48
21
145
101
4342 1 37 35 54 57 202 203
2322
20
15
10 11
10 11
36740
46 47
41 49 50
67
679
8 101 201
201
8 9 201
20
48
39
60
34
MACHINE COMPONENT LOCATIONS
Description
Part
Number
Machine
Location
Schematic
Location
Accumulator Gp - Brake (Charged) 219-2949 1 B-7, C-7
Accumulator Gp - Pilot Oil (Charged) 226-0420 2 D-8
Adapter As 164-5633 3 F-6
Core As - Hydraulic Oil Cooler (Hydraulic Fan, Steering) 191-4600 4 C
-11
Core As - Hydraulic Oil Cooler (Implement / Brake Supply) 261-3853 5 B-5
Cylinder Gp - Lift 9T-9569 6 H-3, H-4
Cylinder Gp - Lift (High Lift) 4Z-6390 7 H-3, H-4
Cylinder Gp - Steering (Left) 6E-1244 8 G-14
Cylinder Gp - Steering (Right) 9T-9568 9 G-14
Cylinder Gp - Tilt 251-1490 10 G-4
Cylinder Gp - Tilt (High Lift) 252-5213 11 G-4
Elbow - (Orificed) 127-9015 12 C-10
Filter Element As - Oil (Hydraulic) (Implement Tank) 4T-313
413 B-5
Filter Element As - Oil (Hydraulic) (Steering Tank) 4T-3134 14 B-11
Filter Gp - Oil (Hydraulic Fan Motor Case Drain) 166-4647 15 C-11
Filter Gp - Oil (Hydraulic Fan Pump Case Drain) 166-4647 16 B-11
Filter Gp - Oil (Implement Pump Case Drain) 166-4647 17 A-4
Filter Gp - Oil (Steering Pump Case Drain) 166-4647 18 B-12
Fitting As (Quick Disconnect)
6V-3965 19
B-13
C-12
Motor Gp - Piston (Hydraulic Fan) 229-0100 20 D-10
P
ump Gp - Gear (Pilot, Brake) 230-0914 21 B-7
Pump Gp - Piston (Hydraulic Fan)
(Std, Mid Range Ambient Temperature)
(High Ambient Temperature)
229-0099
235-0843
22
B-11
23
Pump Gp - Piston (Steering) 229-8604 24 B-12
Pump Gp - Piston (Tandem, Implement) 229-8602 25 B-4
Screen As (Hydraulic Tank) 9T-9227 26 B-11
Screen Gp 7J-2656 27 B-11
B-12
Tank & Filter Gp - Hydraulic (Hydraulic Fan, Steering) 6E-4683 28
Tank & Filter Gp - Hydraulic (Implement, Brake) 237-4228 29 B-5
Valve - Breaker Relief (Implement, Brake Tank) 133-1963 30 B-5
Valve - Breaker Relief (Steering, Hydraulic Fan Tank) 133-1963 31 B-11
Valve - Fluid Sampling (Steering, Hydraulic Fan Oil) 8C-3446 32 C-11
Valve (Filter Bypass) 9J-1988 33 B-11
Valve Gp - Check (Brake Oil Cooler Bypass) 6E-1454 34 C-11
Valve Gp - Check (Pilot) 9T-3096 35 G-4
Valve Gp - Check (Steering Quad) 104-7108 36 C-13
Valve Gp -
Check (Steering Quad) 111-7775 37 D-14
Valve Gp - Combination (Pilot, Brake) 9T-9551 38 D-7
Valve Gp - Demand Fan 191-8735 39 C-9
Valve Gp - Main Control (2-Function) 270-1647 40 B-5
Valve Gp - Manifold & Relief (Main) 229-8721 41 B-3
Valve Gp - Pilot (2-Function) 177-4104 42 H-6
Valve Gp - Pilot (Stic Steering) 249-5615 43 B-15
Valve Gp - Pressure Reducing (Lowering Control) 6E-4286 44 D-13
Valve Gp - Relief (Brake System Backup) 234-0351 45 B-7
Valve Gp - Relief (Line, Lift Head End) 142-4281 46 C-4
Valve Gp - Relief (Line, Tilt Head End) 9T-6720 47 D-4
Valve Gp - Relief (Line, Tilt Rod End) 6E-3185 48 D-4
Valve Gp - Relief (Main) 143-8912 49 B-4
Valve Gp - Relief (Main) 4Z-6240 50 B-4
Valve Gp - Relief (Pilot) 6E-6293 51 C-7
Valve Gp - Relief (Pump Backup) 100-4335 52 E-13
Valve Gp - Relief (Steering Cylinder Crossover) 6E-3985 53 F-15
Valve Gp - Selec
tor & Pressure Control
(Dead Engine, Lift Arm Lower)
6E-3078 54 F-5
Valve Gp - Selector & Pressure Control (Steering) 6E-5566 55 C-13
Valve Gp - Shuttle 6R-0442 56 C-7
Valve Gp - Shuttle (Lift Cylinder) 4T-1860 57 F-4
Valve Gp - Shuttle (Load Signal, Steering, Implement) 4T-1860 58 F-14
Valve Gp - Steering (Std) 6E-2925 59
Valve Gp - Steering Neutralizer (Stic Steering) 9T-7426 60
F-13
C-15
Valve Gp - Unloading 117-7761 61
C-7
Valve (Primary Steering Pump Check) (Secondary Steering) 6E-3780 102
F-12
Pump Gp - Gear (Secondary Steering) 101-4007 101 D-12
Valve - Diverter (Secondary Steering) 2U-7345 103 F-12
Valve Gp - Relief (Secondary Steering) 6E-3986 104 E-12
Valve Gp - Selector & Pressure Control (Secondary Steering) 6E-5566 105 C-13
Valve Gp - Steering (with Secondary Steering) 6E-2923 106 F-13
Accumulator Gp - Ride Control (Charged) 219-7981 201 E-2
Valve Gp - Control 9T-9552 202 D-2
Valve Gp - Solenoid 152-8340 203 D-2
Component Locations
Attachments (Secondary Steering)
Ride Control
Tap Locations
Pressure, Sampling, and Sensor
Tap
Number
Description
Schematic
Location
AA Steer Pilot Supply Pressure Tap D-8
BB Steer Pump Cutoff B-10
CC Fan Pump Cutoff D-7
DD Fan Pump Discharge Pressure Tap C-5
EE Fan Pump Signal Pressure Tap D-13
FF Implement Relief - Front Pump Pressure Tap I-2
GG Implement Relief - Relief Rear Pressure Tap G-2
HH Brake Accumulator D-8
II Implement Pilot Supply B-10
JJ Tilt Cylinder - Head End D-7
KK Tilt Cylinder - Rod End C-5
LL Lift Cylinder - Head End D-13
MM Lift Cylinder - Rod End I-2
NN Ride Control Signal G-2
AA
BB
FF
GG
AA
BB
HH
II
HH
II
FF
GG
DD EE
CC
LINE PATTERNS
Drain / Return Lines
Component Group
Pilot / Load Sensing Pressure
Pressure Line
Attachment
Air Line
CALLOUTS
Taps (Pressure, Sampling,Sensor) by letter
Components by number
YY
52
DRAIN / RETURN LINE
HYDRAULIC CIRCUIT COLOR DESCRIPTIONS
LIFT PUMP OUTPUT
STEERING CIRCUIT
BRAKE/PILOT PUMP OUTPUT
PRIMARY STEERING PUMP CIRCUIT
FAN PUMP OUTPUT
SUPPLY LINE
TILT CYLINDER CIRCUIT
SECONDARY STEERING CIRCUIT
LIFT CYLINDER CIRCUIT
RENR8824-01
20 Page, (Dimensions: 39 inches x 24 inches)
Components are shown installed on a fully operable machine with the key and engine off, transmission shifter
in neutral and with parking brake set.
Refer to the appropriate Service Manual for Troubleshooting, Specifications and Systems Operations.
SCHEMATIC PART NUMBER: 229-8717, CHANGE: 05, VERSION: -
MEDIA NUMBER: RENR8824-01
THIS SCHEMATIC IS FOR THE 990H SERIES II WHEEL LOADER TIER 3
HYDRAULIC SYSTEM
151413121110987654321
15 14 13 12 11 10 9
A
B
C
D
E
F
G
H
32187654
A
B
C
D
E
F
G
H
HS
PS
WARNING
SWITCH
E1
VALVE GP
CHECK
(STEERING QUAD)
111-7775
FITTING AS
(QUICK
DISCONNECT)
6V-3965
FITTING AS
(QUICK
DISCONNECT)
6V-3965
VALVE
FLUID
SAMPLING
(STEERING,
HYDRAULIC
FAN OIL)
8C-3446
CORE AS
HYDRAULIC
OIL COOLER
(HYDRAULIC
FAN,
STEERING)
191-4600
VALVE GP
SELECTOR &
PRESSURE
CONTROL
(SECONDARY
STEERING)
6E-5566
VALVE GP
STEERING
NEUTRALIZER
9T-7426
VALVE GP
STEERING
NEUTRALIZER
9T-7426
VALVE GP
PILOT
(STIC
STEERING)
249-5615
VALVE GP
RELIEF
(SECONDARY
STEERING)
6E-3986
MOTOR GP
PISTON
(HYDRAULIC
FAN)
229-0100
VALVE GP
CHECK
(BRAKE
COOLER
BYPASS)
6E-1454
ELBOW
127-9015
FILTER ELEMENT AS
OIL (HYDRAULIC)
4T-3134
SCREEN AS
(HYDRAULIC TANK)
9T-9227
PUMP GP
PISTON (STEERING)
229-8604
VALVE GP
SELECTOR &
PRESSURE
CONTROL
(STEERING)
6E-5566
VALVE GP
CHECK
(STEERING
QUAD)
104-7108
VALVE GP
PRESSURE REDUCING
(LOWERING CONTROL)
6E-4286
SCREEN GP
7J-2656
TANK & FILTER GP
HYDRAULIC (STEERING,
HYDRAULIC FAN)
6E-4683
VALVE
(FILTER
BYPASS)
9J-1988
FILTER GP
OIL
(HYDRAULIC FAN
PUMP CASE
DRAIN)
166-4647
FILTER GP
OIL
(HYDRAULIC
FAN MOTOR
CASE DRAIN)
166-4647
FILTER GP
OIL
(STEERING
PUMP CASE
DRAIN)
166-4647
PUMP GP
PISTON
(HYDRAULIC FAN)
(STD, MID RANGE AMBIENT
TEMPERATURE)
229-0099
(HIGH AMBIENT
TEMPERATURE)
235-0843
VALVE GP
DEMAND FAN
191-8735
PUMP GP
GEAR
(SECONDARY
STEERING)
101-4007
VALVE
DIVERTER
(SECONDARY
STEERING)
2U-7345
STIC STEER
FITTING AS
(QUICK
DISCONNECT)
6V-3965
FITTING AS
(QUICK
DISCONNECT)
6V-3965
RIGHT
NEUTRALIZER
LEFT
NEUTRALIZER
AIR CONNECTION
AIR CONNECTION
C1 C2
V1 V2
AA
BB
EE
DD
CC
STEERING / FAN DRIVE SCHEMATIC
IMPLEMENT / BRAKE SUPPLY SCHEMATIC
BRAKE
RETURN
LINE
BRAKE
SUPPLY
PRESSURE
PORTS
PRESSURE
SWITCH
PORT
FLUID
SAMPLING
PORT
B1
B2
PS
FS
PP
T
ACCUMULATOR GP
BRAKE (CHARGED)
219-2949
ACCUMULATOR GP
BRAKE (CHARGED)
219-2949
ACCUMULATOR GP
PILOT OIL
(CHARGED)
226-0420
VALVE
SHUTTLE
6R-0442
VALVE GP
UNLOADING
117-7761
VALVE GP
COMBINATION
(PILOT BRAKE)
9T-9551
VALVE GP
RELIEF (PILOT)
6E-6293
PUMP GP
GEAR(PILOT, BRAKE)
230-0914
TANK & FILTER GP
HYDRAULIC
(IMPLEMENT, BRAKE)
237-4228
VALVE GP
RELIEF
(BRAKE SYSTEM BACKUP)
234-0351
FILTER ELEMENT AS
OIL (HYDRAULIC)
4T-3134
CORE AS
HYDRAULIC
OIL COOLER
261-3853
VALVE
BREAKER RELIEF
(IMPLEMENT, BRAKE TANK)
133-1963
FILTER GP
OIL (IMPLEMENT PUMP CASE DRAIN)
166-4647
PUMP GP
PISTON
(TANDEM, IMPLEMENT)
229-8602
VALVE GP
MANIFOLD & RELIEF
(MAIN)
229-8721
VALVE GP
RELIEF (MAIN)
143-8912
VALVE GP
RELIEF (MAIN)
4Z-6240
VALVE GP
RELIEF
(LINE, TILT HEAD END)
9T-6720
VALVE GP
RELIEF
(LINE, LIFT HEAD END)
142-4281
VALVE GP
RELIEF
(LINE, TILT
ROD END)
6E-3185
VALVE GP
MAIN CONTROL
(2-FUNCTION)
270-1647
ACCUMULATOR
219-7981
VALVE GP
SOLENOID
152-8340
VALVE GP
CONTROL
9T-9552
RIDE CONTROL
CYLINDER GP
TILT
251-1490
HIGH TILT
252-5213
VALVE GP
PILOT
177-4104
ADAPTER AS
164-5633
VALVE GP
CHECK
(PILOT)
9T-3096
VALVE GP
SELECTOR &
PRESSURE CONTROL
(DEAD ENGINE,
LIFT ARM LOWER)
6E-3078
VALVE GP
SHUTTLE
(LIFT
CYLINDER)
4T-1860
CYLINDER GP
LIFT
9T-9569
HIGH LIFT
4Z-6390
LIFT
CYLINDERS
TILT
CYLINDER
LEVER LOCKS
TILT LIFT
RACK
BACK
RAISE LOWER
DUMP
RACK
DUMP
LOWER
RAISE
HH
II
GG
FF
NN
MM
LL
KK
JJ
PS
HS
VALVE
BREAKER RELIEF
(STEERING,
HYDRAULIC FAN TANK)
133-1963
VALVE GP
RELIEF
(STEERING
CYLINDER
CROSSOVER)
6E-3985
CYLINDER GP
STEERING (LH)
6E-1244
CYLINDER GP
STEERING (RH)
9T-9568
VALVE GP
RELIEF (PUMP
BACKUP)
100-4335
VALVE GP
STEERING
(STD)
6E-2925
(WITH SECONDARY
STEERING)
6E-2923
VALVE
(PRIMARY STEERING
PUMP CHECK)
(SECONDARY STEERING)
6E-3780
VALVE GP
SHUTTLE
(LOAD SIGNAL,
STEERING, IMPLEMENT)
4T-1860
STEERING
CYLINDERS
RIGHT
TURN
