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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)

2-SECTION PUMP

MAIN AUX.

SPRING(ADJUSTABLE)

VARIABILITY LINE RESTRICTION(VARIABLE)

LINE RESTRICTIONVARIABLE and PRESSURE

COMPENSATED

PRESSURECOMPENSATION

PUMP: VARIABLE andPRESSURE COMPENSATED

ENERGY TRIANGLESHYDRAULIC PNEUMATIC

MEASUREMENT

PRESSURE TEMPERATURE FLOW

ROTATING SHAFTS

UNIDIRECTIONAL BIDIRECTIONAL

PUSH-PULL LEVER PEDALGENERAL MANUAL PUSH BUTTON SPRING

MANUAL CONTROL SYMBOLS

HYDRAULIC MOTORS

FIXEDDISPLACEMENT

VARIABLE DISPLACEMENTNON-COMPENSATED

UNIDIRECTIONAL

BIDIRECTIONAL

HYDRAULIC PUMPS

FLUID STORAGE RESERVOIRS

CROSSING AND JOINING LINES

VALVE ENVELOPES VALVE PORTS

BASIC COMPONENT SYMBOLS

FLUID CONDITIONERPUMP or MOTOR

FLUID POWER SYMBOLS

FIXEDDISPLACEMENT

VARIABLE DISPLACEMENTNON-COMPENSATED

UNIDIRECTIONAL

BIDIRECTIONAL

VALVES

PILOT CONTROL SYMBOLSRELEASED PRESSURE

EXTERNAL RETURN INTERNAL RETURN

REMOTE SUPPLY PRESSURE

SIMPLIFIED COMPLETE INTERNALSUPPLY PRESSURE

ACCUMULATORS

SPRING LOADED GAS CHARGED

SOLENOID or MANUAL

SOLENOID and PILOT

SOLENOID and PILOT or MANUAL

COMBINATION CONTROLS

SOLENOID SERVO THERMAL DETENT

HYDRAULIC AND PNEUMATIC CYLINDERS

DOUBLE ACTINGSINGLE ACTING

BASICSYMBOL

SPRINGLOADED

CHECK VALVES

TWOPOSITION

INFINITEPOSITIONING

FLOW IN ONEDIRECTION

FLOW ALLOWED INEITHER DIRECTION

THREEPOSITION

CROSSFLOW

PARALLELFLOW

INTERNAL PASSAGEWAYS

NORMAL POSITION

A B

P T

A B

P TSHIFTED POSITION INFINITE POSITION

CONTROL VALVES

ATTACHMENT

MANUAL SHUTOFF

SHUTTLE PILOTCONTROLLED

Hydraulic Symbols (Electrical)

Electrical Symbols Table

325-AG135 PK-14

Circuit IdentificationNumber

Wire Color Wire Gauge

Harness identification codeThis example indicateswire 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 ColorCircuit Number Identification

B A

Wire

Wire

(EXAMPLE VALVE)

Current Standard

Transducer(Fluid)

Transducer(Gas / Air)

G

Generator

Electrical WirePressure Switch

MElectric Motor

Pressure Switch (Adjustable)

Temperature Switch

T

PressureSymbol

TemperatureSymbol

LevelSymbol

FlowSymbol

Electrical Symbols (Electrical)

RENR8824December 2006

990H Wheel LoaderHydraulic SystemBWX1-UP

©2006 CaterpillarAll Rights Reserved

Printed in U.S.A.

Description PartNumber

MachineLocation

SchematicLocation

Accumulator Gp - Brake (Charged) 219-2949 1 B-7, C-7Accumulator Gp - Pilot Oil (Charged) 226-0420 2 D-8Adapter As 164-5633 3 F-6Core As - Hydraulic Oil Cooler (Hydraulic Fan, Steering) 191-4600 4 C-11Core As - Hydraulic Oil Cooler (Implement / Brake Supply) 261-3853 5 B-5Cylinder Gp - Lift 9T-9569 6 H-3, H-4Cylinder Gp - Lift (High Lift) 4Z-6390 7 H-3, H-4Cylinder Gp - Steering (Left) 6E-1244 8 G-14Cylinder Gp - Steering (Right) 9T-9568 9 G-14Cylinder Gp - Tilt 251-1490 10 G-4Cylinder Gp - Tilt (High Lift) 252-5213 11 G-4Elbow - (Orificed) 127-9015 12 C-10Filter Element As - Oil (Hydraulic) (Implement Tank) 4T-3134 13 B-5Filter Element As - Oil (Hydraulic) (Steering Tank) 4T-3134 14 B-11Filter Gp - Oil (Hydraulic Fan Motor Case Drain) 166-4647 15 C-11Filter Gp - Oil (Hydraulic Fan Pump Case Drain) 166-4647 16 B-11Filter Gp - Oil (Implement Pump Case Drain) 166-4647 17 A-4Filter Gp - Oil (Steering Pump Case Drain) 166-4647 18 B-12Fitting As (Quick Disconnect) 6V-3965 19 B-13

C-12Motor Gp - Piston (Hydraulic Fan) 229-0100 20 D-10

Pump Gp - Gear (Pilot, Brake) 230-0914 21 B-7

Pump Gp - Piston (Hydraulic Fan)(Std, Mid Range Ambient Temperature)(High Ambient Temperature)

229-0099235-0843

22 B-1123

Pump Gp - Piston (Steering) 229-8604 24 B-12Pump Gp - Piston (Tandem, Implement) 229-8602 25 B-4Screen As (Hydraulic Tank) 9T-9227 26 B-11Screen Gp 7J-2656 27 B-11

B-12Tank & Filter Gp - Hydraulic (Hydraulic Fan, Steering) 6E-4683 28Tank & Filter Gp - Hydraulic (Implement, Brake) 237-4228 29 B-5Valve - Breaker Relief (Implement, Brake Tank) 133-1963 30 B-5Valve - Breaker Relief (Steering, Hydraulic Fan Tank) 133-1963 31 B-11Valve - Fluid Sampling (Steering, Hydraulic Fan Oil) 8C-3446 32 C-11Valve (Filter Bypass) 9J-1988 33 B-11Valve Gp - Check (Brake Oil Cooler Bypass) 6E-1454 34 C-11Valve Gp - Check (Pilot) 9T-3096 35 G-4Valve Gp - Check (Steering Quad) 104-7108 36 C-13Valve Gp - Check (Steering Quad) 111-7775 37 D-14Valve Gp - Combination (Pilot, Brake) 9T-9551 38 D-7Valve Gp - Demand Fan 191-8735 39 C-9Valve Gp - Main Control (2-Function) 270-1647 40 B-5Valve Gp - Manifold & Relief (Main) 229-8721 41 B-3Valve Gp - Pilot (2-Function) 177-4104 42 H-6Valve Gp - Pilot (Stic Steering) 249-5615 43 B-15Valve Gp - Pressure Reducing (Lowering Control) 6E-4286 44 D-13Valve Gp - Relief (Brake System Backup) 234-0351 45 B-7Valve Gp - Relief (Line, Lift Head End) 142-4281 46 C-4Valve Gp - Relief (Line, Tilt Head End) 9T-6720 47 D-4Valve Gp - Relief (Line, Tilt Rod End) 6E-3185 48 D-4Valve Gp - Relief (Main) 143-8912 49 B-4Valve Gp - Relief (Main) 4Z-6240 50 B-4Valve Gp - Relief (Pilot) 6E-6293 51 C-7Valve Gp - Relief (Pump Backup) 100-4335 52 E-13Valve Gp - Relief (Steering Cylinder Crossover) 6E-3985 53 F-15

Valve Gp - Selector & Pressure Control (Dead Engine, Lift Arm Lower) 6E-3078 54 F-5

Valve Gp - Selector & Pressure Control (Steering) 6E-5566 55 C-13Valve Gp - Shuttle 6R-0442 56 C-7Valve Gp - Shuttle (Lift Cylinder) 4T-1860 57 F-4Valve Gp - Shuttle (Load Signal, Steering, Implement) 4T-1860 58 F-14Valve Gp - Steering (Std) 6E-2925 59

Valve Gp - Steering Neutralizer (Stic Steering) 9T-7426 60F-13C-15

Valve Gp - Unloading 117-7761 61 C-7

Valve (Primary Steering Pump Check) (Secondary Steering) 6E-3780 102 F-12Pump Gp - Gear (Secondary Steering) 101-4007 101 D-12

Valve - Diverter (Secondary Steering) 2U-7345 103 F-12Valve Gp - Relief (Secondary Steering) 6E-3986 104 E-12Valve Gp - Selector & Pressure Control (Secondary Steering) 6E-5566 105 C-13Valve Gp - Steering (with Secondary Steering) 6E-2923 106 F-13

Accumulator Gp - Ride Control (Charged) 219-7981 201 E-2Valve Gp - Control 9T-9552 202 D-2Valve Gp - Solenoid 152-8340 203 D-2

Component Locations

Attachments (Secondary Steering)

Ride Control

MACHINE COMPONENT LOCATIONS

4

24

17b

1329 30

16 39

1617a22

23

1244 52 53

106

55 56

5859 102 103 104 105

2 13 14 26 27 28

313338455156

29 30

5861

44 52 53 26 55 56

59 102 103 104 105 106

35 41 49

50 54 57 202

203

14 28 26

2731 332

38 51 56

58 61

19f18 19e17a

19e17b

17a9

19f1812

4

5

5

25

25

15

20

34

60 37

43

423 40

46 47 48

21

145

101

4342 1 37 35 54 57 202 203

2322

20 15

10 11

10 11

3 6 7 40

46 47

41 49 50

6 7

6 79

8 101 201

201

8 9 20120

48

39

60

34

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THIS SCHEMATIC IS FOR THE 990 SERIES II WHEEL DOZER TIER 3PART #: 229-8717 CHG05

Components are shown installed on a fully operable machine with the key and engine off and transmission shifter in neutral.

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

Refer to the appropriate Service Manual for Troubleshooting, Specifications and Systems Operations

DRAIN / RETURN LINE

HYDRAULIC CIRCUIT COLOR DESCRIPTIONSLIFT PUMP OUTPUT

TILT PUMP OUTPUT

STEERING CIRCUIT

BRAKE/PILOT PUMP OUTPUT

PRIMARY STEERING PUMP CIRCUIT

SCAVENGE PUMP

FAN PUMP OUTPUT

SUPPLY LINE

TILT CYLINDER CIRCUIT

SECONDARY STEERING CIRCUIT

LOAD SENSING CIRCUIT

LIFT CYLINDER CIRCUIT

Tap LocationsPressure, Sampling, and Sensor

TapNumber

DescriptionSchematicLocation

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

A

B

C

D

E

F

G

H

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

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

A

B

C

D

E

F

G

H

HS

PS

WARNINGSWITCH

E1

VALVE GPCHECK(STEERING QUAD)111-7775

FITTING AS(QUICKDISCONNECT)6V-3965

FITTING AS(QUICKDISCONNECT)6V-3965

VALVEFLUIDSAMPLING(STEERING,HYDRAULICFAN OIL)8C-3446

CORE ASHYDRAULICOIL COOLER(HYDRAULICFAN,STEERING)191-4600

VALVE GPSELECTOR &PRESSURECONTROL(SECONDARYSTEERING)6E-5566

VALVE GPSTEERING NEUTRALIZER9T-7426

VALVE GPSTEERING NEUTRALIZER9T-7426

VALVE GPPILOT(STIC STEERING)249-5615

VALVE GPRELIEF(SECONDARYSTEERING)6E-3986

MOTOR GPPISTON(HYDRAULICFAN)229-0100

VALVE GPCHECK(BRAKE COOLER BYPASS)6E-1454

ELBOW127-9015

FILTER ELEMENT ASOIL (HYDRAULIC)4T-3134

SCREEN AS(HYDRAULIC TANK)9T-9227

PUMP GPPISTON (STEERING)229-8604

VALVE GPSELECTOR &PRESSURECONTROL(STEERING)6E-5566

VALVE GPCHECK(STEERINGQUAD)104-7108

VALVE GPPRESSURE REDUCING(LOWERING CONTROL)6E-4286

SCREEN GP7J-2656

TANK & FILTER GPHYDRAULIC (STEERING,HYDRAULIC FAN)6E-4683

VALVE(FILTERBYPASS)9J-1988

FILTER GPOIL(HYDRAULIC FANPUMP CASEDRAIN)166-4647

FILTER GPOIL(HYDRAULICFAN MOTOR CASE DRAIN)166-4647

FILTER GPOIL(STEERINGPUMP CASEDRAIN)166-4647

PUMP GPPISTON(HYDRAULIC FAN)

(STD, MID RANGE AMBIENTTEMPERATURE)229-0099

(HIGH AMBIENTTEMPERATURE)235-0843

VALVE GPDEMAND FAN191-8735

PUMP GPGEAR(SECONDARYSTEERING)101-4007

VALVEDIVERTER(SECONDARYSTEERING)2U-7345

STIC STEER

FITTING AS(QUICKDISCONNECT)6V-3965

FITTING AS(QUICKDISCONNECT)6V-3965

RIGHTNEUTRALIZER

LEFTNEUTRALIZER

AIR CONNECTION AIR CONNECTION

C1 C2

V1 V2

AA

BB

EE

DD

CC

STEERING / FAN DRIVE SCHEMATIC IMPLEMENT / BRAKE SUPPLY SCHEMATIC

BRAKERETURNLINE

BRAKESUPPLYPRESSUREPORTS

PRESSURESWITCHPORT

FLUIDSAMPLINGPORT

B1

B2

PS

FS

PP

T

ACCUMULATOR GPBRAKE (CHARGED)219-2949

ACCUMULATOR GPBRAKE (CHARGED)219-2949

ACCUMULATOR GPPILOT OIL(CHARGED)226-0420

VALVESHUTTLE6R-0442

VALVE GPUNLOADING117-7761

VALVE GPCOMBINATION(PILOT BRAKE)9T-9551

VALVE GPRELIEF (PILOT)6E-6293

PUMP GPGEAR(PILOT, BRAKE)230-0914

TANK & FILTER GPHYDRAULIC(IMPLEMENT, BRAKE)237-4228

VALVE GPRELIEF(BRAKE SYSTEM BACKUP)234-0351

FILTER ELEMENT ASOIL (HYDRAULIC)4T-3134

CORE ASHYDRAULIC OIL COOLER261-3853

VALVEBREAKER RELIEF(IMPLEMENT, BRAKE TANK)133-1963

FILTER GPOIL (IMPLEMENT PUMP CASE DRAIN)166-4647

PUMP GPPISTON(TANDEM, IMPLEMENT)229-8602

VALVE GPMANIFOLD & RELIEF(MAIN)229-8721

VALVE GPRELIEF (MAIN)143-8912

VALVE GPRELIEF (MAIN)4Z-6240

VALVE GPRELIEF(LINE, TILT HEAD END)9T-6720

VALVE GPRELIEF(LINE, LIFT HEAD END)142-4281

VALVE GPRELIEF(LINE, TILTROD END)6E-3185

VALVE GPMAIN CONTROL(2-FUNCTION)270-1647

ACCUMULATOR219-7981

VALVE GPSOLENOID152-8340

VALVE GPCONTROL9T-9552

RIDE CONTROL

CYLINDER GPTILT251-1490

HIGH TILT252-5213VALVE GP

PILOT177-4104

ADAPTER AS164-5633

VALVE GPCHECK(PILOT)9T-3096

VALVE GPSELECTOR & PRESSURE CONTROL(DEAD ENGINE, LIFT ARM LOWER)6E-3078

VALVE GPSHUTTLE(LIFTCYLINDER)4T-1860

CYLINDER GPLIFT9T-9569

HIGH LIFT4Z-6390

LIFTCYLINDERS

TILTCYLINDERLEVER LOCKS

TILT LIFT

RACKBACK

RAISE LOWERDUMP

RACK DUMP

LOWER RAISE

HH

II

GG

FF

NN

MM

LL

KK

JJ

PS

HS

VALVEBREAKER RELIEF(STEERING, HYDRAULIC FAN TANK)133-1963

VALVE GPRELIEF(STEERING CYLINDER CROSSOVER)6E-3985

CYLINDER GPSTEERING (LH)6E-1244

CYLINDER GPSTEERING (RH)9T-9568

VALVE GPRELIEF (PUMPBACKUP)100-4335

VALVE GPSTEERING(STD)6E-2925

(WITH SECONDARYSTEERING)6E-2923

VALVE(PRIMARY STEERING PUMP CHECK) (SECONDARY STEERING)6E-3780

VALVE GPSHUTTLE(LOAD SIGNAL,STEERING, IMPLEMENT)4T-1860

STEERINGCYLINDERS

RIGHTTURN