RENR6219-02
November 2011
988H Wheel Loader Tier 3
Hydraulic System
BXY1-3999
Printed in U.S.A.© 2011 Caterpillar, All Rights Reserved
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
RENR6219-02
36 Page, (Dimensions: 48 inches x 35 inches)
5
6
CONTROL VALVE GP
Item Description
Part
Number
Schematic
Location
1 TANK AS. 152-3870 B3
2 TANK GP 153-3602 B3
3 SCREEN AS. 9T-9227 B2,B3
4 SCREEN GP 7J-2656 B2,B3
5 SCREEN 178-0182 B2
6 TUBE-BAFFLE 1U-1570 B2
7 VALVE GP-PILOT 143-2855 B4
8 ACCUMULATOR GP 220-1432 F2,F3
9 COOLER 164-0058 C2
10 VALVE GP-COOLER BYPASS 6E-1454 C2
11 VALVE GP-BRAKE 133-7102 E2
12 FILTER GP 115-2129 C2
13 PUMP GP-SUPPLEMENTAL STER 150-7585 C3
133-8608
133-8609
15 VALVE GP-SHUTTLE 4T-1860 D4
16 VALVE GP-RELIEF 6E-6188 D4
17 VALVE GP-PRESS REDUCING 6E-4286 D4
18 VALVE GP-RELIEF 9T-7419 D4
19 PLUG-ORIFICE 1T-0936 D4
20 VALVE GP-RELIEF 6E-3986 D3
21 VALVE GP-DIVERTER 2U-7345 D3
22 CYLINDER GP-RIGHT 135-3288 E4
23 CYLINDER GP-LEFT 133-8173 E4
24 VALVE GP-CHECK 149-4617 C4
25 VALVE GP-NEUTRALIZER 146-7571 C4
26 PUMP GP-STEER 153-9624 C3
27 VALVE GP-COMP 176-7520 C3
28 VALVE GP-COMP 176-7521 C3
29 PUMP GP-BRAKE/PILOT 177-8924 B1
30 VALVE GP 189-8628 C1
31 VALVE GP 186-6218 C2
32 VALVE GP-RELIEF 139-3544 C2
33 VALVE - FLUID SAMPLING 8C-3446 C1
34 VALVE GP-CHECK 3G-8607 B1
35 FILTER 166-4647 B2
36 VALVE GP-SELECTOR 6E-5566 C3
37 MOTOR GP-PISTON 213-5268 C2
38 VALVE GP-CHECK 9T-3752 C1
228-3636
228-3638
40 VALVE GP-COMP 207-0695 B1
41 VALVE-CHECK 9T-3096 C4
42 VALVE-CHECK 104-7108 C4
133-1963
220-0812
44 TANK GP-EXPANSION 220-2948 B2
45 SWITCH AS.-PRESSURE 175-3244
E2
46 VALVE GP 200-0866
F3
47 CONTROL GP-FOOT BRAKE 169-8258
F3
48 VALVE GP-BRAKE 106-1774
F2
49 SWITCH AS.-PRESSURE 174-4312
F1
50 BRAKE GP-PARK-B 174-1552
F1
51 SENSOR GP-TEMP 131-0427
F4,E4
212-8712
212-8746
212-8721
53 VALVE GP-PRESSURE CONT 6E-4286 D8
54 VALVE GP-SHUTTLE 4T1860 D8
55 VALVE GP-RELIEF 125-9349 D7
56 VALVE GP-RELIEF 117-0161 D8
57 VALVE GP-RELIEF 117-0161 D7
58 VALVE GP-RELIEF 117-0160 D7
117-0159
143-8912
60 ACTUATOR GP 217-6719 C7
61 VALVE-FLOAT 100-6731 C8
62 VALVE 6E-1291 C8
63 ACTUATOR GP 217-6720 D7
64 VALVE 102-4156 C6,C7
65 VALVE GP-RELIEF 172-5481 D7
66
CYL GP-LIFT 173-8613
E8
CYL GP-LIFT (LOGGER) 168-6943
67
CYL GP-TILT 231-1955
E7
CYL GP-TILT (LOGGER) 191-3468
CYL GP-TILT(HIGH LIFT) 152-1644
68
CYL GP-LIFT 173-8612
E6
CYL GP LIFT(LOGGER) 168-6942
69 PUMP GP-IMPLEMENT 216-8978 B7
70 IMPELLER 146-8990 B7
71 COIL AS. 148-2350 B7
72 VALVE GP-CHECK 9T-3096 D8
73 VALVE GP-CHECK 104-7108 B8
74 VALVE GP-SOLENOID 151-7455 B8
75 VALVE GP-SOLENOID 149-2610 B8
76 FILTER 166-4647 B6
77 VALVE GP-BALL 112-1817 B8
78 VALVE GP 9T-9552 C6
79 VALVE GP-SOLENOID 152-8340 C6
80 ORIFICE 8J-6815 C6
81 ADAPTER 204-7143 B7
82 SENSOR GP 143-9176 B7
83 VALVE GP-SHUTTLE 141-1481 B5
84 VALVE GP-CHECK 207-1810 B5
85 ACCUMULATOR 219-7983 D5
86 MOTOR GP - FAN 178-1602 F8
87 CORE AS. 173-6753 F7
88 VALVE-CHECK 9T-5134 F8
89 VALVE GP - SOLENOID 149-2610 F8
90a FILTER GP-SCREEN (FRONT AXLE) 230-3633 F7
90b FILTER GP-SCREEN (REAR AXLE) 230-3633 F7
91 PUMP GP 229-0659 F6
92 PUMP GP 260-3160 F8
Implement System
39 B1
43
PUMP GP-FAN
59 VALVE GP-RELIEF C6
Axle Cooling System
52 VALVE-GP-CONTROL D8
Component Locations
14 VALVE GP-STER D3
VALVE GP-BREAKER & RELIEF B2
Steering and Brake System
Tap
Number
Description
Schematic
Location
A MAIN SYS RLF
B8
B LIFT ROD END LINE RELIEF
D8
C LIFT HEAD END LINE RELIEF
D8
D AUX LINE RELIEF
D7
E AUX LINE RELIEF
D7
F PILOT SUPPLY
C2
G STEER PUMP CUTOFF
C3
H BRAKE CHARGE
B1
I FAN DRIVE SIGNAL
B1
J FRONT BRAKE ACCUMULATOR
F2
K REAR BRAKE ACCUMULATOR
F2
L FRONT BRAKE SUPPLY
F4
M REAR BRAKE SUPPLY
F4
Tap Locations
Pressure, Sampling, and Sensor
8. Front brake accumulator
8. Rear brake accumulator
2. Hydraulic tank
32. Pilot relief valve
12. Pilot filter
43. Vacuum breaker relief valve
F. Pilot pressure tap
K. Rear Accumulator Pressure tap
J. Front Accumulator Pressure tap
33. S.O.S tap
43
K
2
8
32
12
J
8
F
11
2
45
The accumulator charging valve (11) is located on the right side of the machine between the hydraulic tank (2)
and the rear frame. The brake pressure switch (45) sends a signal to the Caterpillar Monitoring System.
33
8
HYDRAULIC TANK ASSEMBLY
The brake/pilot pump (29) is mounted to the right rear side of the pump drive.
The brake/pilot pump supplies oil flow to the brake hydraulic system and pilot
oil to the steering hydraulic system and the implement hydraulic system.
29. Brake/pilot pump
91. Axle cooling pumps
29
91
29
BRAKE/PILOT PUMP
The ride control solenoid (79) is located in the front frame behind and above the
front axle housing. The ride control solenoid is an ON/OFF solenoid. When the ride
control solenoid is energized the head end of the lift cylinders are connected to
the ride control accumulator to absorb the shock that occurs when roading
the machine. The ride control solenoid is a part of the ride control valve
group (78).
The ride control accumulator (85) is mounted horizontally along the inside of
the front right side of the frame, to the rear of the front axle housing.
79
85
78
RIDE CONTROL
The parking brake control valve (48) is located on the right frame rail below the
cab. The parking brake control valve directs oil flow to the parking brake. The
parking brake pressure switch (49) sends the park brake pressure status to the Power
Train ECM.
50. Parking brake
49
48
50
PARKING BRAKE/CONTROL VALVE
35. Steering pump case drain filter.
76. Implement pump case drain filter.
12. Fan pump case drain filter.
In this view, the access panel behind the cab is open, which provides access to the
hydraulic pumps.
26. Steering pump
28. Pump compensator valve
29. Brake/pilot pump
69. Implement pump
G. Steering system pressure tap
12
76
35
26
G
29
69
28
HYDRAULIC PUMPS
16
21
36
17
20
15
18
The steering control valve is located below the cab on the left frame rail. The control valve directs steering system
oil to the steering cylinders and sends signal oil through the ball resolver. Control valve components shown above
are:
15. Ball resolver
16. Back-up relief valve
17. Pressure reducing valve
18. Crossover relief valve
20. Secondary relief valve
21. Diverter valve
36. Selector and pressure control valve
36
The steering pump pressure warning switch is located on the selector and pressure control valve (36) on top of
the fuel tank on the left side of the machine if the machine is equipped with secondary steering.
Warning
Switch
STEERING CONTROL VALVE
87
The axle oil cooler assembly (87) is shown off the machine. The oil cooler assembly
is located on the left side of the machine above the fuel tank. The axle oil cooler
assembly is comprised of two sections with the front axle oil cooler in the lower
section, and the rear axle oil cooler in the upper section. The cooler assembly
removes the heat from the brake and differential oil and returns the oil to the axle
manifold. The cooler oil flows from the manifold and enters the axle at each brake
chamber and at the differential case.
This view shows the axle cooling system components located on the inboard side of
the axle oil cooling assembly. The axle cooling fan motor (86) turns the fan to
draw air through the axle oil coolers. The rear pump (not shown) supplies oil flow
to turn the axle cooling fan motor. A relief valve (88) limits the oil pressure in
the rear axle cooling hydraulic system. The front axle oil filter (90a) and
the rear axle oil filter (90b) are also shown in this view.
88
90a
90b
86
AXLE COOLING ASSEMBLY
The left and right neutralizer valves (25) are mounted at the articulation joint on top of the rear frame. The
quad check valve (24) is located on the rear frame to the rear of the neutralizer valves.
25
25
24
13
The secondary steering pump (13) is splined to the front of the transmission output transfer gear near the
articulation joint. The pump is ground driven and turns when the machine is moving. If the primary steering
pump fails or the engine stops while the machine is moving, the secondary steering pump supplies oil to the
steering system.
SECONDARY STEERING PUMP
NEUTRALIZER/QUAD CHECK VALVES
47
7
1
4
8
9
10
11
12
13
14
22
23
24
26
25
29
30
31
33
34
35
36
37
38
41
42
43
44
45
46
4849
50
51
52
67 66
68
69
72
73
74
76
77
78
85
81
82
83
84
86
87
88
89
90
91
92
A
B
C
D
E
F
G
H
J
K
LM
39
I
COMPONENT AND TAP LOCATIONS
The service brake valve (46) is located below the right brake pedal. The left and
right brake pedals are mechanically connected, allowing the service brake valve to
be actuated by either brake pedal. Also, front service brake oil pressure can be
checked at the front service brake pressure tap (L) and rear service brake oil
pressure can be checked at the rear service brake pressure tap (M).
46
M
L
A hydraulically engaged, multiple disc service brake is located between the
planetaries and the differential at each axle. Each brake contains a piston, discs
and plates. When either brake pedal is depressed, pressure oil moves the piston which
compresses the discs against the plates. The heat from brake friction is removed
by the oil in the differential housing.
Service
Brake
SERVICE BRAKE/VALVE
32
19
27
40
75
70
71
53
54
55
56
57
58
59
60
61
62
63
64
65
80
RENR6219-02
36 Page, (Dimensions: 48 inches x 35 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: 225-5542, CHANGE: 04, VERSION: -
MEDIA NUMBER: RENR6219-02
THIS SCHEMATIC IS FOR THE 988H WHEEL LOADER TIER 3 HYDRAULIC SYSTEM
SCHEMATIC PART NUMBER: 260-0866, CHANGE: 00, VERSION: -
SCHEMATIC PART NUMBER: 259-3116, CHANGE: 04, VERSION: -
1
2
3
4
5
6
7
8
A
B
C
D
E
F
A
C
D
E
F
1
23
4
56
7
8
B
DRAIN / RETURN LINE
LINES GROUP COLOR DESCRIPTIONS
MAIN PUMP OUTPUT
STEERING CIRCUIT
COOLING FAN CIRCUIT
LIFT CIRCUIT
SUPPLY LINE
AXLE COOLING CIRCUIT
BRAKE CIRCUIT
AXLE COOLING PUMP
PILOT/BRAKE PUMP OUTPUT
IMPLEMENT VALVE LOCK CONTROL CIRCUIT
TILT CIRCUIT
AUXILLARY CIRCUIT
SUPPLEMENTAL STEERING
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
VALVE GP
CHECK
104-7108
PUMP GP
IMPLEMENT
216-8978
VALVE GP
SOLENOID
151-7455
VALVE
CHECK
9T-5134
PUMP GP
260-3160
VALVE GP
SHUTTLE
4T-1860
VALVE GP
PRESSURE CONT
6E-4286
VALVE GP
CONTROL
212-8712
212-8746
212-8721
SENSOR GP
143-9176
VALVE GP
BALL
112-1817
VALVE GP
RELIEF
117-0161
VALVE GP
RELIEF
125-9349
VALVE GP
RELIEF
117-0161
CYLINDER GP
LIFT : 173-8613
LIFT (LOGGER) : 168-6943
MOTOR GP
FAN
178-1602
VALVE GP
RELIEF
117-0160
VALVE GP
RELIEF
172-5481
FILTER GP
SCREEN (FRONT AXLE)
230-3633
ACTUATOR GP
217-6720
VALVE
102-4156
COIL AS
148-2350
VALVE
102-4156
ACTUATOR GP
217-6720
VALVE
102-4156
VALVE GP
RELIEF
117-0159
143-8912
PUMP GP
229-0659
VALVE GP
9T-9552
VALVE GP
CHECK
149-4617
PLUG
ORIFICE
1T-0936
VALVE GP
RELIEF
9T-7419
CYLINDER GP
LEFT
133-8173
CYLINDER GP
RIGHT
135-3288
SENSOR GP
TEMPERATURE
131-0427
SENSOR GP
TEMPERATURE
131-0427
VALVE GP
SHUTTLE
4T-1860
VALVE GP
RELIEF
6E-6188
VALVE GP
PRESS REDUCING
6E-4286
VALVE
CHECK
9T-3096
VALVE
CHECK
104-7108
TANK AS
152-3870
SCREEN GP
7J-2656
VALVE GP
SELECTOR
6E-5566
VALVE GP
STER
133-8608
133-8609
VALVE GP
200-0866
CONTROL GP
FOOT BRAKE
169-8258
ACCUMULATOR GP
220-1432
VALVE GP
BRAKE
106-1774
BRAKE GP
PARK B
174-1552
FILTER
166-4647
TUBE
BAFFLE
1U-1570
SCREEN GP
7J-2656
PUMP GP
FAN
228-3636
228-3638
VALVE GP
COMP
207-0695
VALVE GP
186-6218
VALVE GP
RELIEF
139-3544
VALVE GP
BRAKE
133-7102
SWITCH AS
PRESSURE
175-3244
COOLER
164-0058
VALVE GP
COOLER BYPASS
6E-1454
MOTOR GP
PISTON
213-5268
VALVE GP
CHECK
9T-3752
VALVE GP
FLUID SAMPLING
8C-3446
VALVE GP
189-8628
PUMP GP
BRAKE / PILOT
177-8924
VALVE GP
COMP
176-7520
VALVE GP
COMP
176-7521
IMPELLER
146-8990
VALVE GP
CHECK
3G-8607
FILTER GP
115-2129
E
D
LIFT
CYLINDER
TILT
CYLINDER
LIFT
CYLINDER
RACK
LOWER
DUMP
RAISE
A
PUMP CASE
AIR BLEED
PUMP CASE
FILL PORT
FAN SPEED
C
B
FRONT AXLE
REAR AXLE
RIDE
CONTROL
I
H
J
K
BRAKE VALVE RETURN
PUMP
CASE
AIR
BLEED
PUMP
CASE
FILL
PORT
G
STEERING
CYLINDERS
WARNING SWITCH
FRONT BRAKE SUPPLY
REAR BRAKE SUPPLY
FLUID
SAMPLING
PORT
F
STEER
LEFT
NEUTRALIZER
RIGHT
NEUTRALIZER
WARNING
SWITCH
AIR BLEED
IMPL PUMP INLET
PUMP CASE DRAIN
IMPL PILOT SUPPLY
IMPL RETURN
HYDRAULIC
ON/OFF
988H AXLE COOLING SYSTEM
FRONT AXLE
REAR AXLE
M
L
IMPLEMENT SYSTEM
STEERING AND BRAKE SYSTEM
VALVE GP
SOLENOID
149-2610
VALVE GP
CHECK
9T-3096
VALVE
FLOAT
100-6731
VALVE
6E-1291
VALVE GP
SOLENOID
149-2610
ADAPTER
204-7143
ACTUATOR GP
217-6719
ACTUATOR GP
217-6720
CORE AS
173-6753
ACTUATOR GP
217-6719
VALVE GP
SOLENOID
152-8340
FILTER
166-4647
VALVE GP
SHUTTLE
141-1481
VALVE GP
CHECK
207-1810
ORIFICE
8J-6815
ACCUMULATOR
219-7983
VALVE GP
PILOT
143-2855
VALVE GP
NEUTRALIZER
146-7571
TANK GP
153-3602
SCREEN AS
9T-9227
SCREEN AS
9T-9227
SCREEN
178-0182
PUMP GP
STEER
153-9624
SWITCH AS
PRESSURE
174-4312
VALVE GP
DIVERTER
2U-7345
VALVE GP
RELIEF
6E-3986
PUMP GP
SUPPLEMENTAL STER
150-7585
VALVE GP
BREAKER AND RELIEF
133-1963
220-0812
TANK GP
EXPANSION
220-2948
CYLINDER GP
TILT : 231-1955
TILT (LOGGER) : 191-3468
TILT (HIGH LIFT) : 152-1644
CYLINDER GP
LIFT : 173-8612
LIFT (LOGGER) : 168-6942
FILTER GP
SCREEN (REAR AXLE)
230-3633
