PDF Shop Manual Komatsu WA320-6 Wheel Loader - 6 MB
This comprehensive shop manual provides complete service and repair information for the Komatsu WA320-6 Wheel Loader.
It is the definitive guide for technicians, containing step-by-step instructions, specifications, and troubleshooting charts.
From the engine to the hydraulics, this manual covers every aspect of the machine, ensuring repairs are done to factory standards.
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--- Page 1 ---
FOREWORD
CEBM019402
Shop
Manual
WA430-6
WHEEL LOADER
SERIAL NUMBERS WA430-6 A41001 and UP
This material is proprietary to Komatsu America Corp. and is not to be reproduced, used, or disclosed except in accordance
with written authorization from Komatsu America Corp.
It is our policy to improve our products whenever it is possible and practical to do so. We reserve the right to make changes or
add improvements at any time without incurring any obligation to install such changes on products sold previously.
Due to this continuous program of research and development, periodic revisions may be made to this publication. It is
recommended that customers contact their distributor for information on the latest revision.
WA430-6 00-1 c
--- Page 3 ---
FOREWORD SAFETY
Preparations for Work 00
6. When removing components, be careful not to break or
damage the wiring, Damaged wiring may cause
1. Before adding oil or making repairs, park the machine electrical fires.
on hard, level ground and block the wheels to prevent
the machine from moving. 7. When removing piping, stop the fuel or oil from spilling
out. If any fuel or oil drips on the floor, wipe it up
2. Before starting work, lower blade, ripper, bucket, or any immediately. Fuel or oil on the floor can cause you to
other work equipment to the ground. If this is not slip, or can even start fires.
possible, insert the safety pin or use blocks to prevent
the work equipment from falling. In addition, be sure to 8. Gasoline or other fuels should never be used to clean
lock all the control levers and hang warning signs on parts. Clean parts with appropriate solvents.
them.
9. Be sure to assemble all parts again in their original
3. When disassembling or assembling, support the places. Replace any damaged parts or parts that must not
machine with blocks, jacks, or stands before starting be reused.
work. • When installing hoses and wires, be sure that they
can not be damaged by contact with other parts
4. Remove all mud and oil from the steps or other places when the machine is being operated.
used to get on and off the machine. Always use the
handrails, ladders, or steps when getting on or off the 10. When installing high pressure hoses, make sure that
machine. Never jump on or off the machine. If it is they are not twisted. Damaged tubes are dangerous. Be
impossible to use the handrails, ladders, or steps, use a extremely careful when installing tubes for high
stand to provide safe footing. pressure circuits. Check that connecting parts are
correctly installed.
Precautions During Work 00
11. When assembling or installing parts, always use the
1. When removing the oil filler cap, drain plug, or specified tightening torques. When installing protective
hydraulic pressure measuring plugs, loosen them slowly parts such as guards, or parts which vibrate violently or
to prevent the oil from spurting out. Before rotate at high speed, be particularly careful to check that
disconnecting or removing components of the oil, water, they are installed correctly.
or air circuits, first release the pressure completely from
12. When aligning two holes, never insert your fingers or
the circuit.
hand. Be careful not to get your fingers caught in a hole.
2. The coolant and oil in the circuits are hot when the
13. When measuring hydraulic pressure, check that the
engine is stopped; be careful not to get burned. Wait for
measuring tool is correctly assembled before taking any
the oil and coolant to cool before carrying out any work
measurements.
on the oil or water circuits.
14. Take care when removing or installing the tracks of
3. Before starting work, remove the leads from the battery.
track-type machines. When removing the track, the
ALWAYS remove the lead from the negative (-)
track separates suddenly; never let anyone stand at
terminal first.
either end of the track.
4. When raising heavy components (in excess of 25 kg
15. When jump-starting the machine, only use a machine of
(55 lb)), use a hoist or crane. Check that the wire rope,
similar size and voltage. Never use an arc welder or
chains, and hooks are free from damage. Always use
other electrical generating equipment to jump-start the
lifting equipment which has ample capacity. Install the
machine. Carefully review the safety procedures for
lifting equipment at the correct places. Use a hoist or
jump-starting the machine.
crane and operate slowly to prevent the component from
hitting any other part. Do not work with any part still 16. Before starting work, stop the engine. When working on
raised by the hoist or crane. or around a rotating part, stop the engine. When
checking the machine without stopping the engine
5. When removing a cover which is under internal pressure
(measuring oil pressure, revolving speed, temperature,
or under pressure from a spring, always leave two bolts
etc.), be extremely careful not to get rolled or caught in
in position on opposite sides. Loosen the bolts gradually
rotating or moving parts.
and alternately to release the pressure, and then remove
the cover. 17. If the engine is operated for a long time in a place which
is not ventilated well, you may suffer from gas
poisoning. Before starting the engine, open the windows
and doors so that the area is well ventilated.
00-4 ➀
--- Page 4 ---
FOREWORD HANDLING ELECTRIC AND HYDRAULIC EQUIPMENT
★ Injection pressure control valve of fuel supply pump: PCV
(SUMITOMO-2)
★ Speed sensor of fuel supply pump: G (SUMITOMO-3)
★ Pull the connector straight up.
Turn-housing Type (Round Green Connector) 00
★ 140 engine
★ Intake air pressure sensor in intake manifold (CANNON-04):
PIM etc.
1. Disconnect connector (6) according to the following procedure.
A. Turn housing (H1) in the direction of the arrow.
★ When the connector is unlocked, housing (H1) becomes
heavy to turn.
B. Pull out housing (H1) in the direction of the arrow.
★ Housing (H1) is left on the wiring harness side.
2. Connect the connector according to the following procedure.
A. Insert the connector to the end, while setting its groove.
B. Turn housing (H1) in the direction of the arrow until it clicks.
WA430-6 00-23 b
--- Page 5 ---
FOREWORD CONVERSION TABLES
12
Temperature: Fahrenheit Centigrade Conversion
A simple way to convert a Fahrenheit temperature reading into a Centigrade temperature reading or vise versa is to look at the
center or boldface column of figures in this table. These figures refer to the temperature in either Fahrenheit or Centigrade
degrees. If you want to convert from Fahrenheit to Centigrade degrees, consider the center column as a table of Fahrenheit
temperatures and read the corresponding Centigrade temperature in the column at the left. If you want to convert from
Centigrade to Fahrenheit degrees, consider the center column as a table of Centigrade values, and read the corresponding
Fahrenheit temperature on the right.
°C °F °C °F °C °F °C °F
-40.4 -40 -40.0 -11.7 11 51.8 7.8 46 114.8 27.2 81 117.8
-37.2 .35 -31.0 -11.1 12 53.6 8.3 47 116.6 27.8 82 179.6
-34.4 -30 -22.0 -10.6 13 55.4 8.9 48 118.4 28.3 83 181.4
-31.7 -25 -13.0 -10.0 14 57.2 9.4 49 120.2 28.9 84 183.2
-28.9 -20 -4.0 -9.4 15 59.0 10.0 50 122.0 29.4 85 185.0
-28.3 -19 -2.2 -8.9 16 60.8 10.6 51 123.8 30.0 86 186.8
-27.8 -18 -0.4 -8.3 17 62.6 11.1 52 125.6 30.6 87 188.6
-27.2 -17 1.4 -7.8 18 64.4 11.7 53 127.4 31.1 88 190.4
-26.7 -16 3.2 -7.2 19 66.2 12.2 54 129.2 31.7 89 192.2
-26.1 -15 5.0 -6.7 20 68.0 12.8 55 131.0 32.2 90 194.0
-25.6 -14 6.8 -6.1 21 69.8 13.3 56 132.8 32.8 91 195.8
-25.0 -13 8.6 -5.6 22 71.6 13.9 57 134.6 33.3 92 197.6
-24.4 -12 10.4 -5.0 23 73.4 14.4 58 136.4 33.9 93 199.4
-23.9 -11 12.2 -4.4 24 75.2 15.0 59 138.2 34.4 94 201.2
-23.3 -10 14.0 -3.9 25 77.0 15.6 60 140.0 35.0 95 203.0
-22.8 -9 15.8 -3.3 26 78.8 16.1 61 141.8 35.6 96 204.8
-22.2 -8 17.6 -2.8 27 80.6 16.7 62 143.6 36.1 97 206.6
-21.7 -7 19.4 -2.2 28 82.4 17.2 63 145.4 36.7 98 208.4
-21.1 -6 21.2 -1.7 29 84.2 17.8 64 147.2 37.2 99 210.2
-20.6 -5 23.0 -1.1 30 86.0 18.3 65 149.0 37.8 100 212.0
-20.0 -4 24.8 -0.6 31 87.8 18.9 66 150.8 40.6 105 221.0
-19.4 -3 26.6 0 32 89.6 19.4 67 152.6 43.3 110 230.0
-18.9 -2 28.4 0.6 33 91.4 20.0 68 154.4 46.1 115 239.0
-18.3 -1 30.2 1.1 34 93.2 20.6 69 156.2 48.9 120 248.0
-17.8 0 32.0 1.7 35 95.0 21.1 70 158.0 51.7 125 257.0
-17.2 1 33.8 2.2 36 96.8 21.7 71 159.8 54.4 130 266.0
-16.7 2 35.6 2.8 37 98.6 22.2 72 161.6 57.2 135 275.0
-16.1 3 37.4 3.3 38 100.4 22.8 73 163.4 60.0 140 284.0
-15.6 4 39.2 3.9 39 102.2 23.3 74 165.2 62.7 145 293.0
-15.0 5 41.0 4.4 40 104.0 23.9 75 167.0 65.6 150 302.0
-14.4 6 42.8 5.0 41 105.8 24.4 76 168.8 68.3 155 311.0
-13.9 7 44.6 5.6 42 107.6 25.0 77 170.6 71.1 160 320.0
-13.3 8 46.4 6.1 43 109.4 25.6 78 172.4 73.9 165 329.0
-12.8 9 48.2 6.7 44 111.2 26.1 79 174.2 76.7 170 338.0
-12.2 10 50.0 7.2 45 113.0 26.7 80 176.0 79.4 175 347.0
00-42 b WA430-6
--- Page 6 ---
STRUCTURE, FUNCTION AND
MAINTENANCE STANDARD TABLE OF CONTENTS
ELECTRICAL SYSTEM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-317
Machine Monitor System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-317
System Circuit Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-319
Monitor Display Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-322
Speedometer Specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-322
List of Items Displayed on Monitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-324
Machine Monitor Operation Switches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-333
Setting the Machine Monitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-334
Troubleshooting Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-335
Character Display Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-335
Operator Mode Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-336
Service Mode Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-339
Input And Output Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-344
Transmission Controller System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-352
Transmission Controller Gearshifting Control Function . . . . . . . . . . . . . . . . . . . . . 10-352
Cooling Fan Control Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-376
ECSS Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-386
Electric Emergency Steering Function (if equipped) . . . . . . . . . . . . . . . . . . . . . . . 10-388
Power Train Pump Bypass Control Function (if equipped) . . . . . . . . . . . . . . . . . . 10-391
Directional Selector Switch Control Function (if equipped) . . . . . . . . . . . . . . . . . . 10-392
Multi-Function Mono Lever Function (if equipped) . . . . . . . . . . . . . . . . . . . . . . . . 10-395
Joystick Steering Function (if equipped) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-398
Transmission Controller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-405
Work Equipment Controller System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-409
Work Equipment Controller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-415
ELECTRONIC TRANSMISSION CONTROL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-418
Combination Switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-420
Kickdown and Hold Switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-422
Multi-Function Knob (if equipped) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-423
Joystick Steering Knob (if equipped) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-424
KOMTRAX Terminal System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-425
Engine Starting Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-428
Engine Stopping Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-430
Preheating Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-431
Engine Power Mode Selector Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-432
Engine Output Derating Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-433
Automatic Warm-up Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-433
Parking Brake Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-434
Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-436
Speed Sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-436
Torque Converter Oil Temperature Sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-437
Hydraulic Oil Temperature Sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-437
Transmission Oil Temperature Sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-437
Brake Oil Temperature Sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-437
Work Equipment Pump Oil Pressure Sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-438
Steering Pump Oil Pressure Sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-438
Transmission Cutoff Oil Pressure Sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-439
Coolant Level Sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-440
Fuel Level Sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-441
WA430-6 10-5 2
--- Page 7 ---
STRUCTURE, FUNCTION AND
MAINTENANCE STANDARD ENGINE AND COOLING SYSTEM
Suction Valve
Function
• If the fan pump stops, the pressurized oil does not flow into the
motor. Since the motor continues to revolve because of the force of
inertia, the pressure on the outlet side of the motor rises.
• When the oil stops flowing in from inlet port (P), suction valve (1)
sucks in the oil on the outlet side and supplies it to port (MA)
where there is not sufficient oil to prevent cavitation.
Operation
When the pump is started
• If the pressurized oil from the pump is supplied to port (P) and the
pressure on motor inlet (MA) side rises and starting torque is
generated in the motor, the motor starts to revolve.
• The pressurized oil on the motor outlet (MB) side of the motor
returns through port (T) to the tank.
When the pump is stopped
• If the engine is stopped and the input revolution of the fan pump
lowers to 0 rpm, the pressurized oil from the pump is no longer
supplied to port (P). As the pressurized oil is not supplied to (MA)
side of the motor, the motor speed lowers gradually to stop.
• If the motor shaft is revolved by the force of inertia while the oil
flow in (P) is reducing, the oil in port (T) on the outlet side is sent
by suction valve (1) to (MA) side to prevent cavitation.
10-24 1 WA430-6
--- Page 8 ---
STRUCTURE, FUNCTION AND
MAINTENANCE STANDARD POWER TRAIN SYSTEM
A. To power train oil cooler 1. Steering pump and cooling fan pump mounting port
B. To power train pump 2. Power train pump and work equipment pump mounting port
C. Oil pressure pickup port at torque converter outlet 3. Oil level gauge
D. From power train pump 4. Speed sensor
E. Transmission lubricating oil pressure pickup port 5. Breather
F. From power train oil cooler 6. Transmission case (rear)
7. Transmission control valve
8. Transmission case (front)
9. Oil filler pipe mounting port
10. Transmission oil filter
11. Transmission oil temperature sensor
12. Drain plug
13. Torque converter oil temperature sensor
14. Flow control valve
Torque Values
Item N•m lbf ft lbf in
G 98 – 123 72.28 – 90.72 –
H 98 – 123 72.28 – 90.72 –
J 12.7 – 13.7 – 112.40 – 121.26
K 34.3 – 63.7 25.30 – 46.98 –
L 265 – 363 195.45 – 267.73 –
M 49.0 – 68.6 36.14 – 50.60 –
N 44.1 – 53.9 32.53 – 39.75 –
P 34.3 – 63.7 25.30 – 46.98 –
Q 29.4 – 39.2 21.68 – 28.91 –
R 29.4 – 49.0 21.68 – 36.14 –
S 9.8 – 12.7 – 86.74 – 112.40
T 9.8 – 12.7 – 86.74 – 112.40
U 29.4 – 49.0 21.68 – 36.14 –
V 34.3 – 63.7 25.30 – 46.98 –
W 58.8 – 78.5 43.37 – 57.90 –
Outline
• The transmission employed consists of the counter-shaft constant gear mesh mechanism and disc clutch that provides four
forward gear speeds and four reverse gear speeds.
WA430-6 10-43 1
--- Page 9 ---
STRUCTURE, FUNCTION AND
MAINTENANCE STANDARD POWER TRAIN SYSTEM
Forward 2nd Speed
10-62 1 WA430-6
--- Page 10 ---
STRUCTURE, FUNCTION AND
MAINTENANCE STANDARD POWER TRAIN SYSTEM
★ Propulsion force: Hydraulic pressure characteristics of
proportional solenoid
ECMV and Fill Switch
★ For each ECMV, one fill switch is installed.
• If the clutch is filled with oil, the fill switch is turned ON by the
pressure of the clutch. The oil pressure is built up according to this
signal.
Operation of ECMV
• ECMV is controlled with the command current sent from the
controller to the proportional solenoid and the fill switch output
signal.
• The relationship between the proportional solenoid command
current of ECMV, clutch input pressure, and fill switch output
signal is shown in the graph to the right.
• Range A: Before shifting gear (when draining)
• Range B: During filling
• Range C: Pressure regulation
• Range D: During filling (during triggering)
• Point E: Start of filling
• Point F: Finish of filling
★ The logic is that the controller does not recognize completion of
filling even if the fill switch is turned ON during triggering
(Range D).
WA430-6 10-81 1
--- Page 11 ---
STRUCTURE, FUNCTION AND
MAINTENANCE STANDARD DRIVE AXLE SYSTEM
Rear Axle
1. Plate 6. Bevel pinion
2. Disc 7. Shaft
3. Pinion (Teeth: 12) 8. Pressure ring
4. Washer 9. Bevel gear (Teeth: 41)
5. Side gear (Teeth: 24) 10. Case
10-100 1 WA430-6
--- Page 12 ---
STRUCTURE, FUNCTION AND
MAINTENANCE STANDARD STEERING SYSTEM
Servo Valve
P1: Pump discharge pressure port
PE: Control pressure output port
T: Drain port
WA430-6 10-119 1
--- Page 13 ---
STRUCTURE, FUNCTION AND
MAINTENANCE STANDARD STEERING SYSTEM
Turning Right
• If the steering wheel is turned to the right, the output pressure from the Orbitrol valve enters port (Pb) and steering
spool (1) is pushed to the left.
• The oil from the steering pump flows in port (P), and then flows through flow control spool (2) to steering spool (1).
• Load check valve (4) is pushed to the right and opened, conducting the oil flow to the head side of the right steering
cylinder and to the bottom side of the left steering cylinder to turn the machine to the right.
• The oil returning from the right and left steering cylinders is drained through load check valve (3) and port (T1).
10-138 1 WA430-6
--- Page 14 ---
STRUCTURE, FUNCTION AND
MAINTENANCE STANDARD SERVICE BRAKING SYSTEM
SERVICE BRAKING SYSTEM
Brake Piping Diagram
1. Brake valve 7. Parking brake solenoid valve
2. Accumulator (for rear) 8. Parking brake
3. Accumulator (for front) 9. Emergency parking brake release valve
4. Cooling fan pump 10. Charge valve
5. Hydraulic tank 11. Front brake
6. Rear brake
WA430-6 10-157 1
--- Page 15 ---
STRUCTURE, FUNCTION AND
MAINTENANCE STANDARD SERVICE BRAKING SYSTEM
Operation
When brake is operated
• When the brake pedal is pressed, oil pressure (P) supplied through
the hydraulic tank, pump, and brake charge valve to the oil passage
in the brake cylinder, presses piston (2) to the left.
• Accordingly, rotation of discs (4), installed between piston (2),
inner rings (3), and outer ring (5), is stopped and the machine is
braked.
When brake is released
• If the oil pressure is released, piston (2) is returned to the original
position by the reactive force of springs (8) and clearance is made
between inner rings (3) and discs (4), and discs (4) become free.
• The linings bonded to discs (4) have crosshatch grooves in them.
While discs (4) are rotating, oil flows in these grooves to cool the
linings.
10-176 1 WA430-6
--- Page 16 ---
STRUCTURE, FUNCTION AND
MAINTENANCE STANDARD HYDRAULIC SYSTEM
HYDRAULIC SYSTEM
Hydraulic Piping Diagram
WA430-6 10-195 1
--- Page 17 ---
STRUCTURE, FUNCTION AND
MAINTENANCE STANDARD HYDRAULIC SYSTEM
Control of Delivery
• If swash plate angle (a) is increased, the difference between
volumes (E) and (F) is increased and pump delivery (Q) increases.
• Servo piston (11) is used to change swash plate angle (a).
• Servo piston (11) reciprocates straight according to the signal
pressure of the PC and LS valves.
• This straight-line motion is transmitted to rocker cam (3).
• Rocket cam (3), supported on case (2) through ball (9), is tilted
toward the axial direction.
LS Valve
Function
• The LS valve controls the pump delivery according to the stroke of the control lever, or the demand flow for the actuator.
• The LS valve detects the demand flow for the actuator from
differential pressure (ΔPLS) between control valve inlet pressure
(PPLS) and control valve outlet pressure (PLS) and controls main
pump delivery (Q). PPLS is called the LS pump pressure; PLS the
LS pressure; and ΔPLS is the LS differential pressure.
• The pressure loss caused by flow of oil through the opening of the
control valve spool (= LS differential pressure ΔPLS) is detected,
and then pump delivery (Q) is controlled to keep that pressure loss
constant and supply the pump delivery according to the demand
flow for the actuator.
• Main pump discharge pressure (PP), LS pump pressure (PPLS),
and LS pressure (PLS) are led to the LS valve. The relationship
between LS differential pressure (ΔPLS) and pump delivery (Q) changes as shown in this chart.
10-214 1 WA430-6
--- Page 18 ---
STRUCTURE, FUNCTION AND
MAINTENANCE STANDARD HYDRAULIC SYSTEM
1. Suction valve
2. Safety suction valve
3. Spool (lift arm)
4. Pressure compensation valve R
5. Pressure-compensation valve F
6. Safety suction valve
7. Safety suction valve
8. Spool (bucket)
9. Shuttle valve
10. Pressure compensation valve R
11. Pressure compensation valve F
F: Flow control valve
R: Pressure-reducing valve
Torque Values
Item N•m lbf ft lbf in
AA 19.6 – 24.5 14.46 – 18.07 –
BB 9.8 – 14.7 – 86.74 – 130.11
WA430-6 10-233 1
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STRUCTURE, FUNCTION AND
MAINTENANCE STANDARD HYDRAULIC SYSTEM
LS Bypass Plug
1. LS bypass plug
T: Tank circuit (pressure)
PLS: LS circuit
Function
• LS bypass plug releases residual LS pressure (PLS).
• The LS bypass plug lowers the rising speed of LS pressure (PLS) and creates pressure loss in the spool and shuttle valve
with the discarded throttle flow to lower the effective LS differential pressure, and increases the stability.
Operation
The pressurized oil in LS circuit (PLS) flows through clearance filter (a) formed by the clearance between LS bypass plug (1)
and valve body, and then flows through orifice (b) to tank circuit (T).