9Working Hydraulic System_ENGLISG-LG955N

Service Manual of RS8160 Road Roller

SERVICE MANUAL

9

Working Hydraulic System

1

Introduction

Service Manual for LG955N Wheel Loader

CONTENTS 9 Working Hydraulic System.................................................................................9-1 91 System Principle Description..............................................................................9-1 92 Description, Disassembly and Assembly of Hydraulic System Components.....9-2 921 Working Pump.............................................................................................9-2 922 Hydraulic Oil Tank......................................................................................9-8 923 Multitandem Valve....................................................................................9-15 924 Hydraulic Cylinders..................................................................................9-29 93 Service Precautions for Working Hydraulic System.........................................9-48 94 Testing and Adjusting of Working Hydraulic System Pressure........................9-51 941 Measuring and Adjusting of Main Safety Valve Pressure.........................9-51 942 Measuring and Adjusting of Overload Valve Pressure..............................9-53 95 Diagnosis and Solutions for Common Faults of Hydraulic System..................9-55 951 Unexpected Forward Tilt of Bucket..........................................................9-55 952 Boom Sinking............................................................................................9-56 953 Boom Rises Slowly...................................................................................9-58 954 Lifting Incapacity of Boom.......................................................................9-60 955 Bucket Slow Motion..................................................................................9-60 956 Working Incapacity of Bucket...................................................................9-60

1

Service Manual for LG955N Wheel Loader

9

Working Hydraulic System

91 System Principle Description

Fig. 9-1 Hydraulic principle diagram Working device hydraulic system is composed of multitandem valve, flexible shaft operating mechanism, boom cylinder, bucket cylinder, hydraulic oil tank, and pipeline accessories. The multitandem valve is a double valve, one part for bucket, one for boom. Extending, retracting and holding of bucket cylinder and boom cylinder can be realized by operate this valve to realize all kinds of operation requirements. Operate the boom operating handle to move the boom part valve element left and right to connect different oil ports, thereby lifting, lowering or floating of boom can be realized; operate the bucket operating handle, forward tilt and backward tilt of bucket can be realized.

92 Description, Disassembly and Assembly of Hydraulic System 9-1

Service Manual for LG955N Wheel Loader

Components 921

Working Pump Technical parameters Theoretical displacement

160ml/r

Rated rotating speed

2350r/min

Rated pressure

18MPa

Connecting type

Rectangular spline

Fig. 9-2 Structure of working pump 1 Retainer ring

2 Retainer ring

3 Antifriction bearing

4 Lip-type seal ring for rotating shaft

5 Front cover

6 Bearing

7 Rectangular seal ring

8 Gasket

10 Lug seal ring 11 Side plate

12 Driving gear shaft

13 Driven gear shaft

14 Rivet

16 Rear cover block

17 Bolt

15 Label

9 Lug retainer ring

Working pump is double gear pump. It is composed of front pump cover, rotating seal shaft, seal ring, O-shape seal ring, side plate, pump body, bearing, rear pump cover, driving gear and driven gear.

A

P A

Working principle When pump shaft rotates as Fig. 9-3, the gear demeshes on oil absorption chamber side, oil 9-2

T

Service Manual for LG955N Wheel Loader absorption chamber close volume (T) increases and partial vacuum will be formed, oil in the tank will

A

be pressurized into absorption chamber through the oil absorption pipe under the force of atmospheric pressure to fill up the inter-tooth space. As the gear rotates, oil in transition area A will be brought into oil extrusion chamber P, the gear meshes on the extrusion side and the volume decreases to force oil into oil circuit. Fig. 9-3 Working principle

Fault diagnosis of working pump Table 9-2 S/N 1

2 3 4

5

Fault phenomenon

Cause

Oil in hydraulic tank reduces, while oil in transmission box increases. Oil in hydraulic tank increases, while oil in transmission box reduces. Oil leakage of pump body junction surface.

Measure the pressure and Damaged oil seal. replace oil seal ring or working pump. Measure the pressure and Damaged oil seal. replace oil seal ring or working pump. Damaged O-ring or loose Replace the O-ring or fasten the bolt. bolt.

Oil leakage of pump body

Bump body crack.

Excessive wear of spline shaft. Excessive wear of side Abnormal sound produced by plate. steering pump. Out of tolerance of spine shaft. Bearing failure.

6

Insufficient output flow result in Excessive wear of side plate or gear. slow motion.

Elimination method

Check and replace the working pump. Replace the spline shaft or working pump. Replace the side plate or working pump. Replace the spline shaft or working pump. Replace the bearing or working pump. Replace the relevant parts or working pump.

Disassembly and assembly of working p[ump

 ATTENTION Before dismantling the working pump, be sure to carefully read 93 service precautions for working hydraulic system. 9-3

Service Manual for LG955N Wheel Loader Disassembly of working pump 1.

Pressure relief. Start the machine and drive it to the flat spacious place. Raise the boom to the highest position. Tilt the bucket backward, and then shut down the engine. Push the control handle of the pilot valve towards right slowly. Let the bucket tilt forward gently to drain the oil in bucket cylinder.

Fig. 9-4

After the bucket reaches its extreme position, push the handle forward gently. Let the boom fall slowly to drain the oil in boom cylinder. Keep the bucket flat on ground. Then operate the handle left and right, back and forth for 5~6 times to drain the internal oil pressure of the system.

Fig. 9-5 1 Mat

2.

Fix the loader tires with wood blocks stably.

3.

Remove the cab floor mat.

4.

Remove the fixing bolts of maintenance cover

1

plate in the cab, and then take down the plateseat assembly down.

1 Fig. 9-6 1 Maintenance cover plate

9-4

Service Manual for LG955N Wheel Loader

5.

Loosen the bolts that used to fix working pump oil absorption steel pipe on pump oil inlet port, take down the bolts, fission flange and O-ring, and then remove the steel pipe.

1 Fig. 9-7 1 Working pump oil absorption steel pipe

6.

Loosen the bolts that used to fix working pump oil outlet steel pipe on pump oil outlet port, take down the bolts, fission flange and Oring, and then remove the steel pipe.

1 Fig. 9-8 1 Working pump oil outlet steel pipe

7.

Loosen the connecting nuts between working pump and speed changer-torque converter assembly, remove the nuts and gaskets; and then take down the working pump and sealing gasket.

1 2 Fig. 9-9 1 Pump sealing gasket 2 Nut

9-5

Service Manual for LG955N Wheel Loader

Assembly of the working pump 1.

Connect the working pump to transmission box end face with four M12 nuts and gaskets and pump sealing gasket.



75±5 Nm

ATTENTION

 Before the assembly, you should clean the working pump thread holes with KESAI 1 2 Fig. 9-10 1 Pump sealing gasket 2 Nut

1755 high-efficiency cleaner, and then apply KESAI 1545 anaerobic sealant on the studs for sealing.  Be sure to tighten the studs first. 2.

Remove the protector of each oil port, put an O-ring in O-ring groove of working pump oil outlet steel pipe joint, and then fix it on the working pump oil outlet port end face with four M10×55 bolts. 52±10Nm

1 Fig. 9-11 1 Working pump oil outlet steel pipe

3.

Remove the protector of each oil port, put an O-ring in O-ring groove of working pump oil absorption steel pipe joint, and then assemble it to the working pump oil absorption port end face with four M10×55 bolts. 90±20Nm

1 Fig. 9-12 1 Working pump oil absorption steel pipe

9-6

Service Manual for LG955N Wheel Loader

4.

Install

the

maintenance

cover

plate-seat

assembly on the platform in cab with bolts.

1 Fig. 9-13 1 Maintenance cover plate

8.

Fig. 9-14 1 Mat

Reset the cab floor mat.

1

922

Hydraulic Oil Tank

It is used to provide oil to the whole hydraulic system. An oil return filter is designed in the tank to ensure the cleanliness of hydraulic oil. Hydraulic oil filters should be replaced periodically according to requirements in related manual.

9-7

Service Manual for LG955N Wheel Loader To steering pump oil absorption rubber hose

To working pump oil absorption rubber hose

To breather

To steering gear oil return rubber hose

Filter fineness: 120um

To priority valve oil return hose

To multiandem valve oil return hose

Filter fineness: 10um Opening pressure of bypass valve: 0.3MPa

Fill hydraulic oil for about 246L when oil temperature i

Fig. 9-15 Hydraulic oil tank assembly 1 Oil absorption flange assembly 2 Oil filling filter element

3 Oil return block

4 Round oil pointer

7 Oil return filter element

5 Hydraulc oil tank

6 Oil drain plug

Disassembly and assembly of hydraulic oil tank

 ATTENTION Before dismantling the hydraulic oil tank, be sure to carefully read the 93 Service Precautions for Working Hydraulic System in this chapter. Disassembly of hydraulic oil tank 9-8

Service Manual for LG955N Wheel Loader 1.

Pressure relief. Start the machine and drive it to the flat spacious place. Raise the boom to the highest position. Tilt the bucket backward, and then shut down the engine. Push the control handle of the pilot valve towards right slowly. Let the bucket tilt forward gently to drain the oil in bucket cylinder.

Fig. 9-16

After the bucket reaches its extreme position, push the handle forward gently. Let the boom fall slowly to drain the oil in boom cylinder. Keep the bucket flat on ground. Then operate the handle left and right, back and forth for 5~6 times to drain the internal oil pressure of the system. 2.

Fix the loader tires with wood blocks stably.

3.

Remove the oil drain plug on bottom of hydraulic oil tank to drain all hydraulic oil to a clean vessel. Tighten the plug after the draining.

1 1 Fig. 9-17 1 Oil drain plug

4.

1 Fig. 9-18 1 Left platform

1 9-9

Remove the six fixing bolts of left platform.

Service Manual for LG955N Wheel Loader

1 Fig. 9-19 1 Left platform

5.

Lift left platform down.

6.

Loosen the fixing clamps of working pump oil absorption rubber hose and steering pump oil absorption rubber hose respectively.

7. Loosen the fixing clamps between breather rubber hose and breather steel pipe. 8. Remove the fixing bolts of radiator oil return steel pipe, remove the fixing bolt of the steel pipe clamp, take down the bolts, clamp and O-ring.

1 2 3 4 5 Fig. 9-20 1 Radiator oil return steel pipe 2 Working pump oil absorption hose 3 Steering pump oil absorption hose 4 Breather hose5 Pipe clamp

9.

Remove the connecting bolts between oil return block and hydraulic oil tank.

1 2 Fig. 9-21 1 Oil return block2 Bolt

9-10

Service Manual for LG955N Wheel Loader

10. Hang hydraulic oil tank with lifting rope.

Fig. 9-22

11. Remove

the

connecting

bolts

between

hydraulic oil tank and frame, and lift down the hydraulic oil tank.

Fig. 9-23 1 Bolt

1 Fig. 9-24 1 Bolt

1

Assembly of hydraulic oil tank 1.

Apply suitable hydraulic oil on inner surface of working pump and steering pump oil

9-11

Service Manual for LG955N Wheel Loader absorption rubber hose end, place the hose fixing clamps for assembling, lift hydraulic oil tank and put it on left side of rear frame, connect the working pump and steering pump oil absorption rubber hoses to the tank.

2. Fig. 9-25

Apply AT262 thread locking sealant on the M16 bolts, connect the hydraulic oil tank to rear frame with the bolts and gaskets. Adjust the tank assembly to suitable position, tighten the front bolts first, and then tighten the rear bolts. 225±30Nm

1 Fig. 9-26 1 Bolt

Fig. 9-27 1 Bolt

1

3.

Adjust and tighten the fixing clamps of working pump oil absorption rubber hose and

1 2 3 4 5 Fig. 9-28 1 Radiator oil return steel pipe 2 Working pump oil absorption hose 3 Steering pump oil absorption hose 4 Breather hose5 Pipe clamp

steering pump oil absorption rubber hose. 4.

Put O-ring in O-ring groove of radiator oil return steel pipe, fix the pipe on hydraulic oil

9-12

Service Manual for LG955N Wheel Loader tank with four bolts, and tighten the pipe clamps. 78~104Nm 5.

Connect breather rubber hose and breather steel pipe, and tighten the clamps.

6.

Fix the oil return block on hydraulic oil tank with bolts.

1 2 Fig. 9-29 1 Oil return block2 Bolt

7.

Lift and connect the left platform to hydraulic oil tank, install the six M12×30 bolts

1 Fig. 9-30 1 Left platform

1

Fig. 9-31 1 Left platform

1 9-13

Service Manual for LG955N Wheel Loader

8.

Fill hydraulic oil. 1) Fill specified hydraulic oil into the tank through the oil filling port, tighten the oil filler cap until the oil level pointer points at the middle scale. 2) Start the engine, operate to lift and lower the boom, forward tilt and backward tilt the bucket, left steer and right steer the

Fig. 9-32

loader extremely for 2~3 times, in order to fill up the oil cylinders and pipe with hydraulic oil. And then run the engine idly for about 5min to bleed the air in the system out. 3) Shut down the engine, check hydraulic oil level again after the level gets stable, it is appropriate if the level is width Middle Scale±2, add if insufficient.

923

Multitandem Valve

The multiandem valve adopts unitary double-slide-valve structure, which is mainly composed of boom part reversing valve, bucket part reversing valve, safety valve, overload oil supplementary valve and check valves. Oil circuits of the two reversing valves are in series.

9-14

Service Manual for LG955N Wheel Loader

Fig. 9-33 Multitandem valve Oil port P T A1 B1

A2 B2

Component Connected with working pump oil outlet port Back to oil tank after cooling in radiator Connected with piston-side chamber of bucket cylinder Connected with rod-side chamber of bucket cylinder Connected with piston-side chamber of boom cylinder Connected with rod-side chamber of boom cylinder

9-15

1 Check valve, reduce the settlement of boom cylinder 2 Bucket part inlet check valve, prevent bucket cylinder dive 3 Bucket cylinder piston-side overload oil supplementary valve, set pressure 20MPa 4 Bucket cylinder rod-side overload oil supplementary valve, setting pressure 12MPa 5 Main safety valve, setting pressure 18.5MPa

Service Manual for LG955N Wheel Loader

Fig. 9-34 Inner structure of multiandem valve 1 Cotter pin

2 Gasket

3 Round-shoulder pin

4 Boom valve element

5 Compression plate 6 Dust ring

7 Gasket

9 O-ring

10 Plug of pressure measuring port

11 Small end cover

8 O-ring 12 O-ring

14 Check valve

15 O-ring

16 O-ring

20 Spring seat

21 Spring

22 Steel ball

23 Sealing gasket

24 End cover

25 Gasket

26 Bolt

27 Rubber plug

28 Rubber plug

29 End cover

30 Bolt

31 Sealing gasket

35 Safety valve 38 Screw plug 43 O-ring

17 Screw plug

13 Check valve spring

32 Spring pressing seat

18 Valve body

33 Return spring

36 Piston-side overload oil supplementary valve 39 O-ring

40 Bolt

41 Gasket

19 Base plate

34 Spring seat

37 Overload valve block

42 Overload oil supplementary valve block

44 Rod-side overload oil supplementary valve 45 O-ring

46 Bucket valve element

Bucket part reversing valve is a 6/3 valve, which can control the forward tilt, backward tilt and holding of the bucket. Boom part reversing valve is a 6/4 valve, which can control the lifting, holding, lowering and floating of boom. Spring in the boom return sleeve can press the steel ball to the two ends and keep the ball stuck in the V-groove of locating sleeve inwall, so the boom part slide valve element can be fixed in any action position of the four movements. A check valve is designed in inlet port of bucket part reversing valve and boom part reversing valve respectively, the check valves are pressed against the valve seat by spring. Check valve can prevent 9-16

Service Manual for LG955N Wheel Loader hydraulic oil reflux during reversing to overcome “dive” phenomenon. Besides, check valve can produce backpressure for oil returning to keep the system stable.

Working principle of multiandem valve 1) Neutral position (sealed position) The position of bucket slide valve rod and boom slide valve rod is shown in Fig. 9-35. Two both ends of bucket cylinder and boom cylinder are sealed, the two cylinders remain at a certain position, hydraulic oil from working pump flows from port P to port T through the middle oil gallery and then flows back to oil tank. At this point, safety valve is closed, and the system circulates without load.

Fig. 9-35 Cutaway view of multitandem valve 2) Bucket forward tilt Bucket slide valve moves toward right to seal oil duct IV, VI and V; connect oil duct II and III; and connect oil duct VIII and IX. Pressure oil flows from port P into oil duct III through bucket part inlet check valve, then goes through oil duct II to multitandem valve port B1, finally enters into the bucket cylinder rod-side chamber; hydraulic oil in bucket cylinder piston-side chamber flows through multitandem valve port A1, oil duct VIII and IX through port A1, returns back to oil tank, which makes the piston rod of bucket cylinder retract to realize bucket forward tilt. 9-17

Service Manual for LG955N Wheel Loader 3) Bucket backward tilt Bucket slide valve moves toward left to seal oil duct IV, VI and V; connect oil duct I and II; and connect oil duct VII and VIII. Pressure oil flows from port P into oil duct VII through bucket part inlet check valve, then goes through oil duct VIII to multitandem valve port A1, finally enters into the bucket cylinder piston-side chamber; hydraulic oil in bucket cylinder rod-side chamber flows through multitandem valve port B1, oil duct II and oil duct I, returns back to oil tank, which makes the piston rod of bucket cylinder extend to realize bucket backward tilt.

Fig. 9-36 Cutaway view of bucket part reversing valve 4) Boom lifting Boom slide valve moves toward left to seal oil duct III, V and IV; pressure oil flows into oil duct V through port P and bucket part middle oil duct, and goes through the check valve into oil duct VII, finally enters into the boom cylinder piston-side chamber through the multitandem valve port A2. 9-18

Service Manual for LG955N Wheel Loader Hydraulic oil in boom cylinder rod-side chamber flows through multitandem valve port B2, oil duct II and oil duct I, return back to oil tank through multitandem valve port T, which makes the piston rod of boom cylinder extend to realize lifting of boom. 5) Boom lowering Boom slide valve moves toward right to seal oil duct III, V and IV; pressure oil flows into oil duct III through port P and bucket part middle oil duct, finally flows from oil duct II into boom cylinder rod-side chamber through the multitandem valve port B2. Hydraulic oil in boom cylinder pistonside chamber flows through multitandem valve port A2, oil duct VII and oil duct VIII, returns back to oil tank through multitandem valve port T, which makes the piston rod of boom cylinder retract to realize lowering of boom. 6) Boom floating The oil coming from oil pump goes through neutral unload groove into oil return duct and then flows back to oil tank; while the cylinder piston-side is connected to oil return duct VIII via oil duct VII, the cylinder rod-side is connected to oil return duct via middle oil duct, and zero-pressure idle loop is formed in the system. The boom cylinder works in free floating state under the action of working device’s weight and ground acting force.

Fig. 9-37 Cutaway view of boom part reversing valve 7) Main safety valve Safety valve is used to control the system pressure, it is a cartridge valve installed on the multitandem valve, and it’s a pilot operated valve that consisting of main valve part and pilot valve part. The opening and closing of main valve are controlled by the pilot valve part. When the system pressure is low and cannot overcome the pressing force of pilot valve spring to open the pilot valve, the main valve stays in close state, and there is no oil flowing through the small damping hole in the center of main valve element, thus the oil pressure on main valve element both ends is equal. Under the action of the main valve spring, the main valve element will stay in leftmost end position to close the by-pass oil duct between the upper pressure chamber and oil return chamber on valve 9-19

Service Manual for LG955N Wheel Loader body. When the system pressure rises and overcome the pressing force of pilot valve spring to open the pilot valve, a small amount of pressure oil will flow through the small damping hole, and flows from the pilot valve opening port back to the oil return duct of oil chamber. Due to the action of small damping hole, oil pressure on the main valve element right end is less than the left end. When the right-toward acting force, which is acted on the main valve element and produced by pressure difference between the ends, is greater than the pressing force of main valve spring, main valve element will be forced right to valve port, a large amount of pressure oil will overflow back to the tank through the oil return hole, to realize the effect of overload safety protection. The set pressure of safety valve is 18MPa. When the system pressure is lower than the set pressure of safety valve, the pilot valve closes, the oil to the small damping hole stops flowing, the pressure difference disappears and the main valve element resets.

Fig. 9-38 Safety valve 1 Main valve spring

2 Main valve element

4 Pilot valve spring

5 Pressure adjusting screw

3 Pilot valve

8) Overload oil supplementary valve Overload oil supplementary valve is a combination of pilot operated relief valve and check valve. The pilot operated relief valve is installed on the multitandem valve with bolts, two oil ports are connected to the oil ducts of bucket cylinder piston-side and rod-side chamber respectively, the other two are connected to the oil return duct. The check valve is integrated in multiandem valve body, two oil ports are connected to the oil ducts of bucket cylinder piston-side and rod-side chamber respectively, the other two are connected to the oil return duct. 9-20

Service Manual for LG955N Wheel Loader When bucket part reversing valve is in neutral, both rod-side chamber and piston-side chamber of bucket cylinder are sealed. At this point, if severe impacts act on the bucket, the overload oil supplementary valve can prevent dramatic rise of local pressure.

Fig. 9-39 Overload valve 1 Valve sleeve

2 Slide valve

3 Cone valve

6 O-ring

7 Poppet valve

valve seat

11 Pressure adjusting screw

4 Spring

8 Pressure adjusting spring

5 Cone valve 9 O-ring

10 Poppet

12 Lock nut

In the process of the boom lifting, overload oil supplementary valve can conduct oil discharging and supplementing automatically. For instance, when the boom is lifted to a certain position, the piston rod of bucket cylinder will be forced to extend outward, which will make the oil pressure in the bucket cylinder rod-side chamber rise up sharply, the oil cylinder or hydraulic pipe can be damaged under such circumstance. However, because overload valve is designed in the system, it can make the oil trapped in the oil cylinder rod-side chamber return back to the hydraulic oil tank through the overload valve. The volume of oil cylinder rod-side chamber decreases, meanwhile, the volume of oil cylinder piston-side chamber increases and partial vacuum will be formed. At this moment the oil supplementary valve opens to add hydraulic oil into the bucket cylinder piston-side chamber, in order to eliminate the partial vacuum. When the loader is unloading, it can help to make the bucket tip down quickly under the action its own weight, and hits the stop block freely to dump all the materials inside the bucket. During this process, after the bucket barycenter crosses the lower hinge point, the bucket will turn increasingly under the action of gravity; but the movement velocity of bucket cylinder is limited by the oil supply rate of the hydraulic pump. In this case, oil supplementary valve can make the bucket cylinder piston-side chamber overflow timely and at the same time refills oil to the bucket cylinder 9-21

Service Manual for LG955N Wheel Loader rod-side chamber, to make the bucket tip down quickly under the action its own weight, and hits the stop block freely to dump all the materials inside the bucket.

Disassembly and assembly of multitandem valve

 ATTENTION Before dismantling multitandem valve, be sure to carefully read the 93 Service Precautions for Working Hydraulic System in this chapter. Disassembly of the multitandem valve 1

Start the machine and drive it to the front of bearing frame (Put the bearing frame on flat spacious ground in advance), adjust the location of the machine. Raise the boom to the highest position. Tilt the bucket backward to the extreme position, and then shut down the engine. Push the control handle of the pilot valve towards right gently. Let the bucket tilt forward under the action of gravity to drain the

Fig 9-40

oil in bucket cylinder. After the bucket reaches its extreme position, push the handle forward gently, to let the boom falling on the bearing frame. Then operate the handle left and right, back and forth for 5~6 times to release the internal oil pressure of the system. 2

Pull up parking brake and wedge the loader tires with wood blocks stably.

3

Remove the fixing bolts of front cover plate and take the front cover plate down.

1 Fig 9-41 1 Front cover plate

1 2 Fig 9-42 1 Boom part piston-side steel pipe 2 Boom part rod-side steel pipe

4

Loosen the connecting bolts between boom part

piston-side/rod-side

steel

pipes

and

multiandem valve, take down the bolts and Orings, disconnect the steel pipes. 9-22

Service Manual for LG955N Wheel Loader

5

Loosen the connecting bolts between oil inlet block of multiandem valve and P port of multiandem valve, take down the bolts, O-ring and oil inlet block.

1 2 Fig 9-43 1 Bolt 2 Oil inlet block

6

Loosen the connecting bolts between bucket part

piston-side/rod-side

steel

pipes

and

multiandem valve, take down the bolts and Orings, disconnect the steel pipes. 7

Loosen the connecting bolts between oil return steel pipe and multiandem valve, take down the bolts, nuts, gaskets and O-ring, disconnect the steel pipe.

1 2 3 Fig 9-44 1 Bucket part piston-side steel pipe 2 Bucket part rod-side steel pipe 3 Multiandem valve oil return steel pipe

8

Loosen the fixing clamps of bucket slide valve part rod-side and piston-side steel pipes. Loosen the U-shape fixing bolts of boom slide valve part rod-side and piston-side steel pipes. (Doesn’t need to be removed).

1 Fig 9-45 1 Pipe fixing clamp

9-23

Service Manual for LG955N Wheel Loader

1 Fig 9-46 1 Pipe fixing clamp

1 Fig 9-47 1 U-shape fixing bolt

9

Loosen the fixing bolts of the valve operating flexible shaft shield, take down the bolts, nuts, gaskets and shield.

1 2 Fig. 9-48 1 Shield2 Bolt

9-24

Service Manual for LG955N Wheel Loader

10 Remove the cotter pin in the connection between the operating flexible shaft and multiandem valve element, take down the copper pin, gasket and pin shaft.

1 Fig. 9-49 1 Operating flexible shaft

1.

Loosen the fixing bolts between multitandem valve and the valve support, and lift down the valve.

1 Fig. 9-50 1 Bolt

Assembly of the multitandem valve 1.

Install the multitandem valve on the valve support with two M12×145 bolts, gaskets and nuts.

 ATTENTION Do not tighten the bolts in this step, note that big gasket is used here. 90±15Nm

1 Fig. 9-51 1 Bolt 9-25

Service Manual for LG955N Wheel Loader 2.

Remove the protector of each oil port and put an O-ring in O-ring groove of multiandem valve oil return steel pipe, connect the pipe to multiandem valve support with M12×175, M12×145 and M10×65 bolts, nuts and gaskets, tighten these bolts and the bolts used to fix multitandem valve on the valve support (step 1). M12 bolt: 90±15Nm

1 Fig 9-52 1 Multiandem valve oil return steel pipe

M10 bolt: 52±10Nm

3.

Connect the two operating flexible shafts to multiandem valve element with pin shaft, gasket and copper pin.

 ATTENTION Keep the boom slide valve element in floating position (refer to Fig. 9-35), adjust the flexible shafts

until

they

are

coaxial

to

the

corresponding valve elements. The pin shaft 1 Fig. 9-53 1 Operating flexible shaft

should be parallel to ground.

4.

Fix the valve operating flexible shaft shield on valve support with two M8×25 bolts, gaskets and nuts.

1 2 Fig. 9-54 1 Shield2 Bolt

5.

Put O-ring in O-ring groove of bucket part piston-side/rod-side steel pipes, and then

9-26

Service Manual for LG955N Wheel Loader connect the pipes to corresponding oil ports of multiandem valve with four M10×30 bolts and fission flange respectively. 52±10Nm

1 2 3 Fig 9-55 1 Bucket part piston-side steel pipe 2 Bucket part rod-side steel pipe 3 Multiandem valve oil return steel pipe

6.

Put O-ring in O-ring groove of oil inlet block, and then connect the block to P port of multiandem valve with four M10×85 bolts. 52±10Nm

1 2 Fig 9-56 1 Bolt 2 Oil inlet block

7.

Put O-ring in O-ring groove of boom part piston-side/rod-side steel pipes, and then connect the pipes to corresponding oil ports of multiandem valve with four M10×30 bolts respectively. 52±10Nm

1 2 Fig 9-57 1 Boom part piston-side steel pipe 2 Boom part rod-side steel pipe

8.

Tighten the fixing clamps of bucket slide valve part rod-side and piston-side steel pipes. Tighten the U-shape fixing bolts of boom slide valve part rod-side and piston-side steel pipes.

1 Fig 9-58 1 Pipe fixing clamp

9-27

Service Manual for LG955N Wheel Loader

1 Fig 9-59 1 Pipe fixing clamp

1 Fig 9-60 1 U-shape fixing bolt

9.

Fix the maintenance cover plate on front frame with bolts.

1 Fig 9-61 1 Front cover plate

924

Hydraulic Cylinders

9-28

Service Manual for LG955N Wheel Loader

Fig. 9-62 Boom cylinder 1 Seat

2 Piston rod

3 Dust ring

4 Y-shape seal ring

5 Bearing ring

6 Combination seal for shaft 7 Bearing ring

8 Cylinder cover

9 O-ring

10 Cylinder block

12 O-ring

13 Bearing ring

11 Piston

14 Combination seal for hole 15 Boom cylinder sleeve

16 Bolt

17 Gasket

18 Skeleton dust ring

Fig. 9-63 Bucket cylinder 1 Piston rod

2 Dust ring 3 U-shape seal ring 9-29

4 Guide ring

5 Combination seal for shaft

Service Manual for LG955N Wheel Loader 6 Guide ring

7 O-ring

8 O-ring

9 Retainer ring

10 Cylinder cover

11 Cylinder block

12 O-ring

13 Guide ring

14 Combination seal

15 Steel ball

16 Screw

17 Contamination ring

20 Sleeve

21 Gasket

22 Screw

18 Piston

19 Skeleton dust ring

23 Grease cup

24 Sleeve

Notes for installing hydraulic cylinder seal 1

Before installing the seal, grease it properly.

2

Before installing a dust ring, crimp the ring in the way as shown in ①, install it in the way ② will very difficult and more likely to fall off after assembly.

3

When installing piston seals, the opening position of two neighboring seal should be more than 90o different.

Fig. 9-64

Inspection and clean of disassembled hydraulic cylinder 1

Check after disassembling Clean the parts first, and then check whether it is worn, crack or has other problems by visual.

2

Maintenance method Comply to the following procedures to correct the piston rod problem: Planish the axial scratch with oilstone. If the scratch is too depth that can embed a nail, replace the rod immediately. If there is smooth dent, planish the protrudent around with oilstone to adjust; if the dent is too big, replace or re-plate the rod immediately. Important! Repolish the rod after re-plating, the re-plating thickness should be at least 0.25mm. Attention! If the base metal is hurt during planishing, then the rod must be re-plated.

3

Maintenance guides

1

Clearance between piston rod and rod bush If the clearance exceeds 0.25mm, you must replace the bush.

2

Bended piston rod Maximum allowable bending for piston rod is 1mm/m. For measurement, use V-shape blocks support two parallel ends of the rod and put a dial 9-30

Service Manual for LG955N Wheel Loader indicator in the middle, rotate the piston rod and record the highest and the lowest value in the meantime.

Disassembly and assembly of boom cylinder

 ATTENTION Before dismantling the boom cylinder, be sure to carefully read the 93 Service Precautions for Working Hydraulic System in this chapter. Disassembly of the boom cylinder 1.

Start the machine and drive it to the front of bearing frame (Put the bearing frame on flat spacious ground in advance), adjust the location of the machine. Raise the boom to the highest position. Tilt the bucket backward to the extreme position, and then shut down the engine. Push the control handle of the pilot valve towards right gently. Let the bucket tilt

Fig. 9-65

forward under the action of gravity to drain the oil in bucket cylinder. After the bucket reaches its extreme position, push the handle forward gently, to let the boom falling on the bearing frame. Then operate the handle left and right, back and forth for 5~6 times to release the internal oil pressure of the system. 9-31

Service Manual for LG955N Wheel Loader

2.

Disconnect the connection between the steel pipes and rubber hoses of boom cylinder rodside and piston-side respectively.

1 2 Fig. 9-66 1 Boom cylinder rod-side rubber hose 2 Boom cylinder piston-side rubber hose

3.

Bind the cylinder body with lifting rope and lift it up a bit. Then loosen boom cylinder front pin fixing bolt, remove the bolt and gasket.

Fig. 9-67

4.

Then loosen boom cylinder front pin fixing bolt, remove the bolt and gaskets.

1 2 Fig 9-68 1 Pin2 Bolt

5.

Disassemble boom cylinder front pin, remove the adjusting gasket, and avoid scratching the

1 Fig 9-69 1 Pin

pin during the operation. 9-32

Service Manual for LG955N Wheel Loader

6.

Remove the fixing bolts of front mud fender, rotate the mud fender clockwise for a certain angle

to

assembling

make of

the boom

disassembling

and

cylinder

pin

rear

convenient.

Fig 9-70 1 Pin

1

7.

Loosen the fixing bolt of boom cylinder rear pin, take down the bolt and gasket.

1 Fig 9-71 1 Pin

8.

Remove boom cylinder rear pin, lift the cylinder away.

1 Fig 9-72 1 Pin

9-33

Service Manual for LG955N Wheel Loader

9.

Remove the fixing bolts of boom cylinder rodside steel pipe.

10. Remove the fixing bolts of boom cylinder rodside pipe clamp, take down the bolts, steel pipe and O-ring.

1 2 3 Fig 9-73 1 Pipe clamp 2 Boom cylinder rod-side steel pipe 3 Bolt

11. Remove the fixing bolts of boom cylinder rodside steel pipe, take down the bolts, steel pipe and O-ring.

1 2 3 Fig 9-74 1 Bolt 2 Boom cylinder piston-side steel pipe 3 Bolt

9-34

Service Manual for LG955N Wheel Loader

Assembly of the boom cylinder 1.

Remove the relevant protectors, put an O-ring in O-ring groove of boom cylinder rod-side steel pipe, and then fix the pipe on rod-side oil port of boom cylinder with four M10×30 bolts. 52±10Nm

2.

Fix the rod-side steel pipe on boom cylinder block with pipe clamp and two M8×20 bolts.

1 2 3 Fig 9-75 1 Pipe clamp 2 Boom cylinder rod-side steel pipe 3 Bolt

3.

Put an O-ring in O-ring groove of boom cylinder piston-side steel pipe, and then fix the pipe on piston-side oil port of boom cylinder with two M10×50 and two M10×55 bolts. 52±10Nm

4.

Fix the piston-side steel pipe on boom cylinder block with a M10×20 bolt.

1 2 3 Fig 9-76 1 Bolt 2 Boom cylinder piston-side steel pipe 3 Bolt

5.

Bind the cylinder body with lifting rope and lift it to assembling position.

Fig. 9-77

9-35

Service Manual for LG955N Wheel Loader

6.

Apply some grease on boom cylinder rear pin, and then use it to connect boom cylinder to the front frame.

 ATTENTION 1) Note that piston-side pipes should be on the outside, do not make mistakes. 2) Do not damage the grease cup when knocking the pin. 1 Fig 9-78 1 Pin

7.

Install the fixing bolt of boom cylinder rear pin. 225±52Nm

1 Fig 9-79 1 Pin

8.

Apply some grease on boom cylinder front pin, add a gasket, and then start the engine. Operate pilot handle to adjust stroke of boom cylinder piston rod, keep its connecting hole aligned with the pin joint hole on boom, and connect them with pin.

 ATTENTION Be 1 Fig 9-80 1 Pin

careful

when

assembling

the

boom

cylinder, the screw seat on piston rod head should be on outside; use proper numbers of gaskets to ensure the clearance between piston rod head end face and boom is within 0.5~1.5mm. 9-36

Service Manual for LG955N Wheel Loader 9.

Fix boom cylinder front pin on piston with bolt.

1 Fig 9-81 1 Pin

10. Remove the protectors, put an O-ring in O-ring groove of boom cylinder rubber hoses, fix the hoses on boom cylinder rod-side and pistonside steel pipes with fission flange and four M10×30 bolts respectively.

 ATTENTION 1 2 Fig. 9-82 1 Boom cylinder rod-side rubber hose 2 Boom cylinder piston-side rubber hose

The two hoses should be parallel and free of distortion. 52±10Nm

11. Reset the front mud fender and install the fixing bolts.

Fig 9-83 1 Pin

1

12. Add grease to boom cylinder front pin grease cups until there is grease squeezed out of the fitting surface. 9-37

Fig 9-84

Service Manual for LG955N Wheel Loader

13. Add grease to boom cylinder rear pin grease cups until there is grease squeezed out of the fitting surface.

Fig 9-85

Disassembly and assembly of bucket cylinder

 ATTENTION Before dismantling the bucket cylinder, be sure to carefully read the 93 Service Precautions for Working Hydraulic System in this chapter. Disassembly of the bucket cylinder 1 9-38

Fig 9-86

Pressure relief.

Service Manual for LG955N Wheel Loader Start the machine and drive it to flat spacious place. Raise the boom to the highest position. Tilt the bucket backward to the extreme position, and then shut down the engine. Push the control handle of the pilot valve towards right gently. Let the bucket tilt forward under the action of gravity to drain the oil in bucket cylinder. After the bucket reaches its extreme position, push the handle forward gently. Let the boom falling under the action of gravity to drain the oil in boom cylinder. Keep the bucket flat on ground. Then operate the handle left and right, back and forth for 5~6 times to release the internal oil pressure of the system. 2

Wedge the tires with wood blocks stably.

1.

Loosen the fixing bolts of flat fender, take down the bolts, gaskets and flat fender.

1 Fig 9-87 1 Flat fender

2.

Loosen the connecting bolts between the bucket cylinder piston-side rubber hose and piston-side steel pipe, and then remove the bolts, fission flange and rubber hose, protect the oil ports in time. During

disassembling

the

hydraulic

connections, do not loosen the connection bolt 1 Fig 9-88 1 Bucket cylinder piston-side rubber hose

rashly and completely to avoid oil bursting out 9-39

Service Manual for LG955N Wheel Loader due to incomplete pressure relief.

3.

Loosen the connecting bolts between the bucket cylinder rod-side rubber hose and rodside oil port, and then remove the bolts, fission flange and rubber hose, protect the oil port in time.

1 Fig 9-89 1 Bucket cylinder rod-side rubber hose

4.

Bind the cylinder body with lifting rope and keep the rope with a certain pretension force.

1 Fig. 9-90 1 Bucket cylinder

5.

Loosen the fixing bolt of bucket cylinder front pin, take down the bolt and gasket.

1 Fig. 9-91 1 Pin

9-40

Service Manual for LG955N Wheel Loader

6.

Remove bucket cylinder front pin.

 ATTENTION Avoid scratching the pin during the operation

1 Fig. 9-92 1 Pin

7.

Loosen the fixing bolt of bucket cylinder rear pin, take down the bolt and gasket.

1 Fig. 9-93 1 Pin

8.

Remove bucket cylinder front pin and adjusting gaskets, lift bucket cylinder down and put it on suitable support.

1 2 Fig. 9-94 1 Pin2 Grease pipe

9-41

Service Manual for LG955N Wheel Loader 9.

Remove the front-end fixing bolts of bucket cylinder piston-side steel pipe.

10. Remove the rear-end fixing bolts of bucket cylinder piston-side steel pipe, take down the bolts, steel pipe and O-ring. Take measures to protect the disconnected oil ports in time.

1 Fig 9-95 1 Steel pipe

Assembly of the bucket cylinder 1.

Remove the protector of each oil port, put an O-ring in O-ring groove of bucket cylinder piston-side steel pipe, and fix the pipe on piston-side oil port with two M10×50 and two M10×55 bolts and gaskets separately. 52±10Nm

2. 1 Fig 9-96 1 Steel pipe

Fix the piston-side steel pipe on bucket cylinder block with a M10×20 bolt.

3.

Bind the cylinder body with lifting rope and lift it to assembling position.

Fig 9-97

4.

Apply some grease on pin. Lift the cylinder up to proper position with lifting rope, use the pin to connect the cylinder to front frame.

9-42

Fig 9-98

Service Manual for LG955N Wheel Loader

 ATTENTION Put gaskets on connecting end faces, ensure the fitting clearance between two end faces is within 0.5~1.5mm by using different type and number of gaskets.

5.

Fix the rear pin on front frame with gasket and a M16×30 bolt. 225±52Nm

1 Fig. 9-99 1 Pin

1 2 Fig. 9-100 1 Pin2 Grease pipe

6.

Install the graease pipe.

7.

Start the engine and operate pilot handle to adjust stroke of bucket cylinder piston rod, keep its connecting hole aligned with the pin joint hole on rocker arm, and connect them with pin.

9-43

Fig 9-101

Service Manual for LG955N Wheel Loader

8.

Fix the front pin on rocker arm with gasket and a M16×30 bolt. 225±52Nm

Fig. 9-102 1 Pin

1

9.

Put an O-ring in O-ring groove of bucket cylinder piston-side rubber hose, fix the hoses on bucket cylinder piston-side steel pipe with fission flange and four M10×30 bolts.

 ATTENTION Do not distort the hose. 52±10Nm

1 Fig. 9-103 1 Bucket cylinder piston-side rubber hose

10. Put an O-ring in O-ring groove of bucket cylinder rod-side rubber hose, fix the hoses on bucket cylinder rod-side oil port with fission flange and four M10×30 bolts.

 ATTENTION Do not distort the hose. 52±10Nm 1 Fig. 9-104 1 Bucket cylinder rod-side rubber hose

9-44

Service Manual for LG955N Wheel Loader

11. Fix the flat fender on bucket cylinder piston rod head with two M10×20 bolts and gaskets.

1 Fig 9-105 1 Flat fender

12. Add grease to grease cup until there is grease squeezed out of the fitting surfaces.

1 Fig 9-106 1 Grease nozzle

1 Fig 9-107 1 Grease nozzle

9-45

Service Manual for LG955N Wheel Loader

93 Service Precautions for Working Hydraulic System The most common fault for high-pressure and high-precision hydraulic devices is that fouling (alien material) occurs in the hydraulic circuit. Thus, pay special attention to the cleanliness when adding hydraulic oil or removing and refitting the hydraulic devices. 1

Pay attention to working environment. Avoid adding hydraulic oil, replacing filter or repairing machine in rain or at windy and dirty place.

2

Removing

and

servicing

machine

on

outdoor site. Chances are that fouling will enter the equipment if removal and service are done on outdoor site; moreover, it is difficult to

Fig. 9-108

appraise

equipment’s

performance

after

eliminating the faults. So this is only suitable for replacing components. Removal and service of the hydraulic devices should be conducted in special dust-free workshop and the performance of the hydraulic devices should be appraised with special testing device. 3

Seal up the openings. After removing the pipes or components, all

Fig. 9-109

9-46

Service Manual for LG955N Wheel Loader openings should be sealed with cap, adhesive paper or plastic bag so as to prevent fouling or dirt from entering them. If you let the openings be exposed or clogged with rags, fouling is liable to get into them or the leaking oil will stain the surrounding places, which is not allowed to happen. Instead of draining oil on the ground, you should collect the drained oil and take it back to handle it on your own. 4

Prevent any fouling or dirt from entering the system during the oil refilling operation. Prevent any fouling or dirt from being mixed into the hydraulic oil when refilling hydraulic oil and be sure to keep the oil filler and the surrounding surface clean as well as use clean oil pump and container. Utilizing oil cleaning device will filter the fouling deposited during the storage period from the oil, which is more

Fig. 9-110

effective for refilling oil. 5

The hydraulic oil should be changed when the oil temperature is high. When the hydraulic oil or other oil is hot, their fluidity is good and the deposited sludge is easy to be flushed away by the oil. Therefore, it is recommended to change oil when the oil is hot. Discharge the old oil fully (not only the oil in the hydraulic oil tank but also the oil in the filter and plugs of the pipeline) as possible as you can when changing oil. If there is old

Rinsing oil

oil residual, the fouling and deposited sludge will be mixed with the new oil, shortening the service life of the new oil. 6

Flushing operation. The fouling, oil sludge and old oil in the hydraulic oil circuit should be flushed away

Fig. 9-111

9-47

Service Manual for LG955N Wheel Loader with rinsing oil when changing oil after the disassembly and assembly of the hydraulic devices. Normally, flushing is conducted for two times: primary flushing with rinsing oil and

secondary

flushing

with

specified

hydraulic oil.

7

Cleaning operation. Get rid of the sludge and fouling in the hydraulic oil circuit with oil cleaning device after repairing the hydraulic device (pump, control valve, etc.) or when the machine is operating. The oil cleaning device is used to remove the ultrafine granule that cannot be removed by the filter in the hydraulic device, which is a very effective cleaning tool.

Fig.8 9-112 Torque requirements.

The securing operation should be conducted in strict accordance with the torque required in this manual during the process of removal, refitting and service of the hydraulic system. Excessive or insufficient torque will lead to hydraulic oil leakage.

 ATTENTION For the torque that is not indicated, please refer to relevant requirements in chapter 0 General of this manual. 1.

Bleeding of working hydraulic system After replacement of hydraulic pump, hydraulic cylinder, hydraulic pipe, joint and all kinds of valves, bleeding operation must be done. The specific bleeding steps are as follows: 1) Open the filler cap of hydraulic tank. 2) Start the engine; run the engine at idle for 5 minutes, and then retract and extend all cylinders from bottom for about 2~3 times, keep the stroke within 50~60 mm. 3) Keep the engine run at low speed, and then retract and extend all cylinders fully for about 3~5 times to bleed the air in hydraulic circuit. 4) After the bleeding, set the machine and working device in standard position, check hydraulic oil level and tighten the filler cap. 9-48

Service Manual for LG955N Wheel Loader 5) Shut down the engine, check for leakage.

94 Testing and Adjusting of Working Hydraulic System Pressure 941 Measuring and Adjusting of Main Safety Valve Pressure Pressure measuring Required oil temperature for measurement: 45~55oC. Pressure measurement tools Pressure gauge with the measuring range of 40MPa, quick-change pressure measuring joint, piezometer tube Pressure measuring point Measuring port on multiandem valve oil inlet block Pressure measuring standard 18MPa Pressure measuring method (take boom in lowering position for example) Put the working device flat on ground, pull up

1 Fig 9-113 1 Pressure measuring port

the parking brake, and then wedge the tires with wood blocks tightly, shut down the engine. Operate the operating handle for10 times and turn steering wheel left and right for about 5 times to release residual pressure in hydraulic circuit; prepare the measurement tools. 1

Connect measuring tools  Remove the plug of pressure measuring port;  Connect the quick-change pressure measuring joint to pressure measuring port;  Connect piezometer tube to the quick-change pressure measuring joint;  Connect the pressure gauge with measuring range

Fig. 9-114

of 40MPa to the tube. 2

Start the engine, and operate the pilot operating handle to retract the bucket. After the bucket gets to its extreme position, increase the accelerator to the maximum size (2200r/min) gradually. Observe the pressure gauge and record the steady pressure value, and that is the current working pressure for working hydraulic system. 9-49

Service Manual for LG955N Wheel Loader 3

To get more accurate result, put the boom in other positions and repeat the measurement.

ATTENTION After the measurement, disassemble the measurement tools and wipe them clean.

Adjusting method Multiandem valve of LG953N wheel loader is installed on front frame and the main safety valve is on the side of oil inlet port, covered with lead seal. Remove the lead seal and loose the lock nut, rotate the adjusting screw to change main safety valve set pressure.

Fig. 9-115 Pressure adjusting of main safety valve 1 Lock nut

2 Lead seal

3Adjusting screw

 Rotate the adjusting screw clockwise to increase the set pressure.  Rotate the adjusting screw anticlockwise to decrease the set pressure.  The pressure will change 4MPa if turning the adjusting screw for one circle. So each time you adjust the pressure, it’s better to turn the adjusting screw for 1/4~1/5 circle, measure the pressure according to the method exposed in this manual and tighten the lock nut after the adjustment.  Lock nut: 35±5Nm

9-50

Service Manual for LG955N Wheel Loader

942 Measuring and Adjusting of Overload Valve Pressure Pressure measuring Required oil temperature for measurement: 45~55oC. Pressure measurement tools Pressure gauge with the measuring range of 40MPa, quick-change pressure measuring joint, piezometer tube Pressure measuring point Measuring port on bucket cylinder piston-side steel pipe Pressure measuring standard 20MPa Pressure measuring method (take boom in lowering position for example)

1 Fig 9-116 1 Pressure measuring port

Put the working device flat on ground, pull up the parking brake, and then wedge the tires with wood blocks tightly, shut down the engine. Operate the operating handle for10 times and turn steering wheel left and right for about 5 times to release residual pressure in hydraulic circuit; prepare the measurement tools. 4

Connect measuring tools  Remove the plug of pressure measuring port;  Connect the quick-change pressure measuring joint to pressure measuring port;  Connect piezometer tube to the quick-change pressure measuring joint;  Connect the pressure gauge with measuring range

Fig. 9-117

of 40MPa to the tube. 5

Start the engine, and operate the pilot operating handle to retract the bucket. After the bucket gets to its extreme position, increase the accelerator to the maximum size (2200r/min) gradually. Observe the pressure gauge and record the steady pressure value, and that is the current working pressure for working hydraulic system.

6

To get more accurate result, put the boom in other positions and repeat the measurement.

ATTENTION After the measurement, disassemble the measurement tools and clean them up.

Adjusting method Multiandem valve of LG953N wheel loader is installed on front frame. Bucket piston-side and rod9-51

Service Manual for LG955N Wheel Loader side overload valves are on the bottom of multiandem valve, the piston-side one is on bucket side, while the rod-side one is on cab side. Bothe the overload valves are covered with lead seal.

Fig. 9-118 Pressure adjusting of overload valve 1 Lock nut

2 Lead seal

3Adjusting screw

 Rotate the adjusting screw clockwise to increase the set pressure.  Rotate the adjusting screw anticlockwise to decrease the set pressure.  The pressure will change 2MPa if turning the adjusting screw for one circle.  Lock nut: 35±5Nm

ATTENTION  Because set pressure of bucket cylinder piston-side overload valve is higher than that of main safety valve, so its pressure must be adjusted on specialized test-bed other than on the machine directly.  Pressure of rod-side overload valve cannot be adjusted for now.

95 Diagnosis and Solutions for Common Faults of Hydraulic System 951

Unexpected 9-52

Forward

Tilt

of

Service Manual for LG955N Wheel Loader

Bucket Fault phenomena: When operating handle of pilot valve is in neutral position, the bucket tilt forward unexpectedly. Fault analysis: Because link mechanisms are used in working device, when the bucket is under retract state and operating handle of pilot valve is in neutral position, the bucket cylinder piston-side chamber will suffer extra force caused by self-weight. At this point, if there is leakage in piston-side chamber, it will result in unexpected forward tilt of bucket. Six situations can cause the leakage in piston-side chamber of bucket cylinder: 1

Obvious external leakage exists in pipelines, joints and fitting surfaces from the piston-side chamber to multitandem valve.

2

Multitandem valve bucket slide vale part fails to go back to neutral position (because valve element gets stuck, valve element of pilot valve cannot reset or there are faults exist in the valve body, such as sand holes and grooves that connect to piston-side chamber).

3

While inner leakage exists in bucket cylinder, leakage also exists from rod-side chamber to oil outlet port.

4

Low overload pressure for bucket cylinder piston-side overload valve (may caused by damaged pressure adjusting spring, valve element stuck in open position, dirt exists in the conical fitting surface between valve element and valve body, or there are defects exist in the valve body, such as sand holes and grooves that connect to piston-side chamber).

5

Leakage exists in bucket cylinder piston-side oil compensation valve (may caused by damaged reset spring, valve element stuck in open position, dirt exists in the conical fitting surface between valve element and valve body, or there are defects exist in the valve body, such as sand holes and grooves that connect to piston-side chamber)

6

Excessive wear of selector valve body or element, which result in fit clearance between valve body and valve element is far more than design value.

Diagnosis and solutions: 1

Six situations that cause leakage are listed above and the simplest and easiest to diagnose is the first one: Start the machine and lift the boom to a certain height, retract the bucket to its extreme position, and then observe the pipelines, joints and fitting surfaces from the piston-side chamber to multitandem valve to find out whether there are obvious external leakage phenomena exist.

2

If the first situation is being excluded, consider the second situation: Start the machine and operate pilot valve handle to lift the boom to highest position, and retract the bucket to its extreme position, and then shut down the engine, disassemble the two pilot pipes that connected to two ends of multitandem valve bucket slide vale part. At this point, if the 9-53

Service Manual for LG955N Wheel Loader unexpected forward tilt phenomenon disappeared, then we can come to a conclusion that the fault is caused by pilot valve, which causes multitandem valve bucket slide vale part fails to go back to neutral position. Disassemble and clean the pilot valve or replace it. Otherwise, check the third situation. 3

For the third situation, we can do some simple check: Start the machine and operate pilot valve handle to lower the boom to lowest position, and retract the bucket to its extreme position, and then shut down the engine, disconnect bucket cylinder piston-side rubber hose and diver it to hydraulic oil tank. Start the machine again, operate the pilot valve handle to backward tilt the bucket, observe whether there is oil comes out from piston-side oil port continually. If there is, which means server inner leakage exists in bucket cylinder, the cylinder needs to be repaired or replaced. Otherwise, check the fourth and fifth situations.

4

For the fourth and fifth situations, method of pressure detection can be used: Connect a 0250Bar pressure gauge to gauge port of bucket cylinder piston-side chamber. Start the machine and operate pilot valve handle to extend the bucket to its extreme position; step on the gas and operate pilot valve handle to lift the boom, at the same time, check whether the reading on the gauge reach the design value when the boom is lifting. If not, either situation mentioned in the first place is possible, the overload valve or oil compensation valve for bucket cylinder pistonside chamber need to be checked and cleaned.

5

If situation 1 to situation 5 have been excluded and the fault still exists, then stop the machine, low boom and bucker to lowest positions and disassemble multitandem valve bucket slide valve part, look through the valve element, valve opening and their fitting situation.

6

Excessive wear of selector valve body or element, which result in fit clearance between valve body and valve element is far more than design value.

952

Boom Sinking

Fault phenomena: When operating handle of pilot valve is in neutral position, the boom sinks automatically and exceeds allowed range. Fault analysis: When the boom is lifted and stays in a certain height, the boom cylinder piston-side chamber will suffer extra force caused by self-weight. At this point, if there is leakage in piston-side chamber, the boom will fall automatically. Four situations can cause the leakage in piston-side chamber of boom cylinder: 1

Obvious external leakage exists in pipelines, joints and fitting surfaces from the piston-side chamber to multitandem valve.

2

Multitandem valve boom slide vale part fails to go back to neutral position (because valve element gets stuck, valve element of pilot valve cannot reset or there are defects exist in the 9-54

Service Manual for LG955N Wheel Loader valve body, such as sand holes and grooves), which cause boom cylinder rod-side chamber connect to pump, or piston-side chamber connect to oil return port. 3

While inner leakage exists in boom cylinder, leakage also exists from rod-side chamber to oil outlet port.

4

Excessive wear of selector valve body or element, which result in fit clearance between valve body and valve element is far more than design value.

Diagnosis and solutions: 1

Four situations that cause leakage are listed above and the simplest and easiest to diagnose is the first one: Start the machine and lift the boom to highest height, and then observe the pipelines, joints and fitting surfaces from the piston-side chamber to multitandem valve to find out whether there are obvious external leakage phenomena exist.

2

If the first situation is being excluded, consider the second situation: Start the machine and operate pilot valve handle to lift the boom to highest position, and retract the bucket to its extreme position, and then shut down the engine, disassemble the two pilot pipes that connected to two ends of multitandem valve bucket slide vale part. At this point, if the boom sinking phenomenon disappeared, then we can come to a conclusion that the fault is caused by pilot valve, which causes multitandem valve boom slide vale part fails to go back to neutral position. Disassemble and clean the pilot valve or replace it. Otherwise, check the third situation.

3

For the third situation, we can do some simple check: Start the machine and operate pilot valve handle to lift the boom to highest position, and retract the bucket to its extreme position, and then shut down the engine, disconnect boom cylinder piston-side rubber hose and divert it to hydraulic oil tank. Start the machine again, operate the pilot valve handle to lower the boom, observe whether there is oil comes out from piston-side oil port continually. If there is, which means server inner leakage exists in boom cylinder, the cylinder needs to be repaired or replaced. Otherwise, check the fourth situation.

4

If situation 1 to situation 3 have been excluded and the fault still exists, then stop the machine, low boom and bucker to lowest positions and disassemble multitandem valve boom slide valve part, look through the valve element, valve opening and their fitting situation.

953

Boom Rises Slowly

Fault phenomena: When the diesel engine is running under rated speed, operate pilot valve handle to lift the boom from lowest to highest position, the time it needed exceeds full load lifting time. Fault analysis: Consider the characteristics of Hydraulic power units, the reason for boom lifting slowly: insufficient flow from hydraulic pump to cylinder. Nine situations are listed below that may cause insufficient flow from hydraulic pump to 9-55

Service Manual for LG955N Wheel Loader cylinder: 1

Severe external leakage exists in joints, pipelines, valves and fitting surfaces from pump to boom cylinder piston-side chamber.

2

The hydraulic oil contain a lot of bubble or turns black, or goes bad, and its viscosity has been changed.

3

Blocked oil absorption filter or oil absorption pipe, which make the working pump hard to suck oil.

4

Severe inner leakage exists in working pump.

5

Severe inner leakage exists in boom cylinder (caused by cylinder scoring or damaged sealing element).

6

Low adjusting pressure of multitandem valve main safety valve (may caused by damaged pressure adjusting spring, valve element stuck in open position, or there are defects exist in the valve body, such as sand holes and grooves that connect to oil return chamber).

7

Severe inner leakage exists between oil inlet channel an oil return channel of multitandem valve body (caused by sand hole or breakage of valve body).

8

Excessive wear of selector valve element or valve opening of multitandem valve boom slide valve part, which result in fit clearance between valve body and valve element is far more than design value.

9

Insufficient opening of multitandem valve (because selector valve element gets stuck, valve element of boom cylinder piston-side pilot valve cannot reset or there are sand holes and grooves exist in the valve body, or low setting pressure of combination valve that result in insufficient pilot pressure).

Diagnosis and solutions: 1

For all situations mentioned above, firstly, we should start the machine and lift the boom, check out whether there is obvious external leakage exists in pipelines, joints and fitting surfaces from working pump to boom cylinder piston-side chamber.

2

If there is no severe external leakage, then basic inspection should be done: Whether the hydraulic oil level is above “LOW” level, whether there is too much bubble in hydraulic oil or the oil turns black. Add hydraulic oil if necessary; if the oil turns bad, clean the tank and the whole hydraulic system, and then replace the oil.

3

If the hydraulic oil is good, then start the machine and operate pilot handle to retract the bucket, at the same time, listen carefully and check whether there is screaming in working pump. If there is, which means the pump have severe oil absorption problem, check and clean oil absorption filter and rubber hoses.

9-56

Service Manual for LG955N Wheel Loader 4

If there is no screaming phenomenon, check the forth situation: Start the machine, operate the pilot valve to load the pump for 1-2 minutes, then shut down the engine; carefully touch the shell of working pump, if it feels too hot, then we can come to a conclusion that severe inner leakage exist in working pump, which causes the oil shortage problem.

5

For the fifth to ninth situations, we need to do some simple tests first: Connect a 0-40MPa pressure gauge to gauge port of multitandem valve P port. Start the machine and operate pilot valve handle to pressurize the hydraulic system, at the same time, check whether the reading on the gauge reach the design value. If not, check situation 5 to 8 one by one.

6

For the fifth situation, start the machine and operate pilot valve handle to lower the boom to lowest position, and retract the bucket to its extreme position, and then shut down the engine, disconnect boom cylinder piston-side rubber hose and divert it to hydraulic oil tank. Start the machine again, operate the pilot valve handle to lower the boom, observe whether there is oil comes out from piston-side oil port continually. If there is, which means server inner leakage exists in boom cylinder, the cylinder needs to be repaired or replaced.

7

For situation 6: Check and clean main safety valve, if there is irreparable damage for valve element or valve body, please replace the safety valve.

8

If situation 6 and 7 are being excluded and the system pressure still fails to reach design value, then focus on situation 7 and 8. Disassemble multitandem valve boom slide valve part, look through the valve element, valve opening and their fitting situation.

9

If the hydraulic system pressure reaches design value but the boom still lifting slow, check the ninth situation: Operate pilot valve handle to lower the boom and bucket to their lowest positions, and then open the spring-free end cover (the one with short axial dimension) of multitandem valve boom slide valve part, force the valve element to do axial movement, check whether the rod can get to the right positions, whether it can return to neutral position smoothly.

954

Lifting Incapacity of Boom

Fault phenomena: When the diesel engine is running under rated speed, operate pilot valve handle to lift the boom under full load, the boom fails to be lifted. Fault analysis: The most direct reason for lifting incapacity of boom is low pressure of boom cylinder piston chamber. Primary reasons for low pressure in boom cylinder piston chamber: 1

Low overload pressure for main safety valve of multitandem valve (may be caused by damaged pressure adjusting spring, valve element stuck in open position, or there are defects exist in the valve body, such as sand holes and grooves that connect to oil return chamber). 9-57

Service Manual for LG955N Wheel Loader 2

Severe inner leakage of working pump, because that the system cannot build up pressure or the system pressure cannot reach design value.

3

Severe inner leakage exists in boom cylinder (caused by cylinder scoring or damaged sealing element ).

4

Severe inner leakage exists between oil inlet channel an oil return channel of multitandem valve body (caused by sand hole or breakage of valve body), because that the system cannot build up pressure or the system pressure cannot reach design value.

Diagnosis and solutions: Focus on the four reasons mentioned above and refer to Boom raises slowly for troubleshooting.

955

Bucket Slow Motion

Refer to Boom raises slowly for troubleshooting.

956

Working Incapacity of Bucket

Refer to Lifting incapacity of boom for troubleshooting.

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