Manual Training Hydraulic System Caterpillar Backhoe Loaders

Service Training MALAGA

Backhoe Loaders

VI. HYDRAULIC SYSTEM 1. 2. 3. 4. 5. 6. 7.

Load Sensing/Pressure Compensated Hydraulic System - Resolver Network Hydraulic Pump Torque Limiter Steering System Loader Valve Control Backhoe Valve control

Sara MARCH 1997

BACKHOE LOADERS CHAPTER : Hydraulic System

Hydraulic System Component Checklist I Directions: Use this sheet to take notes during the presentation (i.e. location, functions) . During a lab exercise, use this as a checklist when identifying components. B Series

C Series Hydraulic tank

Hydraulic oil filter(s)

Pump

Pump control valve

Loader valve group

Backhoe valve group

Implement controls

Pump supply pressure test port

Signal pressure test port

Torque Limiter

Page:

VI-1

Page: VI-2

QUIZ LOAD SENSING/PRESSURE COMPENSATING TWO VALVE OPERATION

BACKHOE LOADERS

B

CHAPTER : Hydraulic System

A


QUIZ 1.-

If two valves are operated at the same time and at valve A the work port pressure (signal pressure) is 1800 psi and at valve B the work port pressure is 700 psi then: System pressure will be : 1800 psi + _________ psi = _________ psi CALCULATIONS : ð Valve A work port pressure = 1800 psi ÆP across pressure reducing valve = _________ psi - _________ psi = _________ psi ÆP across control spool = _________ psi - _________ psi = _________ psi ð Valve B work port pressure = 700 psi ÆP across pressure reducing valve = _________ psi - _________ psi = _________ psi ÆP across control spool = _________ psi - _________ psi = _________ psi

2.-

If two valves are operated at the same time and at valve A the work port pressure (signal pressure) is 3000 psi and at valve B the work port pressure is 1000 psi then: System pressure will be : _________ psi + _________ psi = _________ psi CALCULATIONS : ð Valve A work port pressure = 3000 psi ÆP across pressure reducing valve = _________ psi - _________ psi = _________ psi ÆP across control spool = _________ psi - _________ psi = _________ psi ð Valve B work port pressure = 1000 psi ÆP across pressure reducing valve = _________ psi - _________ psi = _________ psi ÆP across control spool = _________ psi - _________ psi = _________ psi

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VI-3

Page:

428C AND 438C BACKHOE LOADER HYDRAULIC SYSTEM DUAL TILT CYLINDERS

VI-4 END COVER

Directions: Label all valves, the tanks, filters, cooler, pump, and HMU.

BACKHOE LOADERS

Hydraulic System Component Checklist


INLET MANIFOLD

Page: VI-5

428C, AND 438C BACKHOE LOADERS HYDRAULIC SYSTEM DUAL TILT CYLINDERS PUMP

TANK END COVER E-STICK HMU STICK

SWING BOOM INLET MANIFOLD

S T E E R

L I F T

T I L T

A U X.

BACKHOE LOADERS

RIGHT STABILIZER LEFT STABILIZER


BUCKET

Page: VI-6

428B, AND 438B BACKHOE LOADER HYDRAULIC SYSTEM PUMP TANK INLET MANIFOLD EXT. STICK

HMU

STICK

BOOM RH STAB LH STAB. END COVER

S T E E R

A U X.

T I L T

L I F T

BACKHOE LOADERS

SWING


BUCKET

Page:

428C AND 438C SIGNAL NETWORK

VI-7

BOOM

SWING

LEFT RIGHT STABILIZER STABILIZER

BUCKET

STICK PRIMARY RESOLVER SECONDARY RESOLVER

HMU

TO PUMP CONTROL VALVE

BACKHOE LOADERS

LOADER LIFT


LOADER TILT

Page: VI-8

416B-438B SIGNAL NETWORK STABILIZER STABILIZER BOOM

SWING

BUCKET

STICK PRIMARY RESOLVER SECONDARY RESOLVER

TO PUMP CONTROL VALVE

BACKHOE LOADERS

LOADER HAND METERING TILT UNIT


LOADER LIFT

BACKHOE LOADERS CHAPTER : Hydraulic System "C" Series Hydraulic Pump Components Checklist Directions: Fill in the blanks next to the letters with the correct term. Use this sheet to take notes during the slide presentation.

IMPLEMENT AND STEERING PUMP LOW PRESSURE STANDBY SIGNAL

B

PUMP OUTPUT

C D

A F E A

B

C

D

E

F Page:

VI-9

Page:

IMPLEMENT AND STEERING PUMP

VI-10

LOW PRESSURE STANDBY SIGNAL

PRESSURE CUTOFF

PUMP OUTPUT

LARGE ACTUATOR

SWASHPLATE

TORQUE LIMITER SMALL ACTUATOR AND BIAS SPRING

BACKHOE LOADERS


MARGIN SPOOL

Page: VI-11

416B-438B HYDRAULIC PUMP ENGINE OFF SIGNAL

PUMP OUTPUT

LARGE ACTUATOR

YOKE PAD SWASH PLATE

PRESSURE COMPENSATOR PISTON & BARREL ASSEMBLY

SMALL ACTUATOR & BIAS SPRING

BACKHOE LOADERS

FLOW COMPENSATOR


DRIVE SHAFT

Page: VI-12

TORQUE LIMITER NORMAL ADJUSTMENT SCREW SIGNAL SPRING SLOT

PASSAGE TO TANK SIGNAL

BACKHOE LOADERS

REDUCED FLOW

SPOOL


SLEEVE

ACTUATOR PISTON

Page:

416B - 438B HYDRAULIC PUMP

VI-13

TORQUE LIMITER - OPEN

TORQUE LIMITER SIGNAL

BACKHOE LOADERS

PRESSURE COMPENSATOR


FLOW COMPENSATOR

PUMP OUTPUT


IMPLEMENT AND STEERING PUMP TORQUE LIMITER REDUCES FLOW PUMP OUTPUT

SIGNAL

MARGIN SPOOL

LARGE ACTUATOR

TORQUE LIMITER PASSAGE TO TANK

SMALL ACTUATOR AND BIAS SPRING

C Series Torque Limiter ¥ Torque limiter operation - Destrokes pump as pressure increases - Spring force varies with swashplate angle

The torque limiter monitors the pump swashplate angle and the pump signal pressure. The torque limiter will not allow the pump to go to full stroke as system pressure increases above the torque limiter setting. The allowable pump displacement is inversely proportional to the pump discharge pressure. The higher the pressure, the less pump flow is available. The pressure setting of the torque limiter varies with the swashplate angle. The greater the swashplate angle, the lower the pressure setting. If the pump is at maximum flow and the signal pressure increases above the torque limiter setting, the torque limiter opens and directs some of the signal oil to the tank through a slot in the torque limiter spool. A pressure drop occurs across the orifice in the signal line which results in a slight loss of the actual signal pressure. The margin spool then moves up and allows supply oil to the large actuator piston. The pump will then destroke.

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VI-14


TORQUE LIMITER NORMAL ADJUSTMENT SCREW SIGNAL SPRING SLEEVE

SLOT

SPOOL

ACTUATOR PISTON

REDUCED FLOW PASSAGE TO TANK SIGNAL

¥ Maintains input torque setting

The torque limiter will maintain control over the swashplate as long as the signal pressure remains the same or increases for the high flow demanded. During this condition, the torque limiter remains open and continues to meter some of the signal oil to the tank. The reduced pump flow will be at a sufficient level to maintain the input torque setting. If the cylinder pressure continues to increase, the torque limiter will again open and destroke the pump more. In summary, full pump supply pressure is always available. However, flow is regulated to maintain a required maximum input torque from the engine. Full pump flow is available when the signal pressure is below the torque limiter setting.

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VI-15


416B - 438B HYDRAULIC PUMP TORQUE LIMITER - OPEN

TORQUE LIMITER SIGNAL

FLOW COMPENSATOR

PUMP OUTPUT

PRESSURE COMPENSATOR

B Series Torque Limiter ¥ Maintains input torque setting

If the pump is at maximum flow and the signal pressure increases above the torque limiter setting, the torque limiter opens and directs some of the signal oil to the tank. A pressure drop occurs across the orifice in the signal line which results in a slight loss of the actual signal pressure. The margin spool then moves up and allows supply oil to the large actuator piston. The pump will then destroke. The torque limiter will maintain control over the swashplate as long as the signal pressure remains the same or increases for the high flow demanded. During this condition, the torque limiter remains open and continues to meter some of the signal oil to the tank. The reduced pump flow will be at a sufficient level to maintain the input torque setting. If the cylinder pressure continues to increase, the torque limiter will again open and destroke the pump more. In summary, full pump supply pressure is always available. However, flow is regulated to maintain a required maximum input torque from the engine. Full pump flow is available when the signal pressure is below the torque limiter setting.

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VI-16


ENGINE RPM VS. THE TORQUE LIMITER SETTING

E N G I N E

Engine RPM and the torque limiter setting are directly proportional to one another. At points A and B the input torque is the same; However, at the higher low idle engine speed for point B, the torque limiter setting can be set higher.

B

R P M

A

TORQUE LIMITER SETTING SYSTEM PRESSURE VS. FLOW RATE The allowable pump displacement is inversely proportional to the pump discharge pressure. For line B at 43 gpm (maximum flow) as shown here, the system pressure is less than maximum system pressure. If the system pressure increases the maximum flow rate is reduced by the torque limiter. The pump at the higher operating pressure is now in the torque limiter control range. As pressure continues to increase the flow rate is further reduced.

S Y S T E M P R E S S U R E

3000 PSI

A TORQUE LIMITER CONTROL RANGE

B

B

FLOW RATE Page:

VI-17

43 GPM

A


Torque Limiter Adjustments Adjustments to the torque limiter can be made, but are not usually required. To determine if the torque limiter is at fault or whether the engine is at fault, try the following. Check torque converter stall. If the torque stall specification is incorrect and the implement hydraulics is causing the engine to stop, then probably the engine is at fault. DO NOT ADJUST THE TORQUE LIMITER. If torque converter stall specification is correct, but the hydraulic system causes the engine to die. The torque limiter may to be adjusted. Before adjusting the torque limiter make sure that pump standby pressure, maximum system pressure and margin pressure are correct.

B Series Torque Limiter Adjustments 1) Check Low Idle and adjust to above 950 rpm. Set at least to 970. The fuel pump low idle spring tends to droop after a number of hours are put on the machine. 2) Operate boom down at low idle against the boom stop. If the hydraulic system no longer causes the engine to die, no further adjustment is required. 3) If the engine still dies. Back out the torque limiter to reduce the spring setting. 4) Operate boom down at low idle against the boom stop. Increase the torque limiter setting until the engine dies. Back out the torque limiter about a quarter of a turn. 5) Restart machine. Operate boom down at low idle against the boom stop. If the engine does not die the torque limiter has been adjusted correctly.

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VI-18


C Series Torque Limiter Adjustments 1) Check Low Idle and adjust to above 950 rpm. Set at least to 970. The fuel pump low idle spring tends to droop after a number of hours are put on the machine. 2) Operate boom down at low idle against the boom stop. The engine rpm should drop about 100 to 140 rpm from the low idle setting. If this occurs, then no further adjustment is required. 3) If the engine rpm drops lower than 100 to 140 rpm. Back out the torque limiter to reduce the spring setting until engine lug falls between 100 to 140 rpm less than low idle. 4) If engine rpm lug is less than a 100 rpm, the torque limiter setting should be increased.

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VI-19


SYSTEM TESTING System Tests The performance of the 416-446 hydraulic systems can be easily tested. Two pressure gauge fittings are installed on the hydraulic oil pump. Before performing any pump tests or making adjustments to the pump control valve, measure and record the machine cycle times. If the cycle times are within specification, checking low pressure standby or margin pressure may not be required unless the system is overheating. Cycle time checks will also indicate if all or some of the implements in the system are operating within specification. This information can be helpful in determining if the pump or the implement is at fault. If all cycle times are too slow, margin pressure may be set too low. If the machine is too responsive, the margin pressure may be set too high. Connect an 8T0859 gauge to each pressure fitting. The oil lines for the gauges should be long enough so the gauges can be observed from the operator's station.With the gauges installed, follow the testing and adjusting procedures in the Service Manual for maximum system pressure and low pressure standby. When performing the margin pressure test, follow the Service Manual Procedures with the following exceptions: 1. Using a 6V8731 Union in the tilt circuit is not required. 2. Activate any implement slowly and watch the gauges. If margin pressure needs to be adjusted, the following method is quicker and safer for the mechanic: 1. Compare margin pressure to low pressure standby. 2. Mentally add to or subtract from low pressure standby about the same amount required to set margin pressure to specification. Since both pressures are adjusted by the same screw, an adjustment to one also affects the other. This relationship, however, is not linear. 3. Make this adjustment to the flow compensator (margin spool) while the machine is in low pressure standby. 4. Recheck margin pressure after adjusting low pressure standby. NOTE: Due to the signal pressure limiter, the steering circuit is commonly used to check margin pressure because the steering circuit pressure is below maximum system pressure. When steering is stalled, a signal of approximately 14000 kPa (2050 psi) is sent to the pump. The pump increases flow due to oil being sent to tank through the signal pressure limiter. Pump supply pressure increases. The difference between the pump supply pressure and the steering signal is margin pressure.

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VI-20


B & C Series Backhoe Loader Hydraulic System Lab Sheet Perform the Following Tasks: ¥ Warm up hydraulic system. ¥ Record initial system pressures below: Low pressure standby Maximum system pressure Margin Pressure ¥ Invert front bucket fully and lower to the ground. Record cycle times for loader lift below: Loader lift cycle time specification Test One

Test Two

Test Three

Average Cycle time ¥ Adjust Low Pressure Standby to 150 psi. Record cycle times for loader lift below: Test One

Test Two

Test Three

Average Cycle time ¥ Adjust Low Pressure Standby to 450 psi. Record cycle times for loader lift below: Test One

Test Two

Test Three

Average Cycle time ¥ Reset Low Pressure Standby to 320 psi. for the B series and 350 psi for the C series. times and margin pressure. Test One Average Cycle time Margin Pressure

Describe your conclusions:

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VI-21

Test Two

Test Three

Recheck cycle

BACKHOE LOADERS CHAPTER : Hydraulic System BACKHOE LOADER HYDRAULIC TESTS DATE

_______________________________

MACHINE MODEL NAME/CODE

_______________________________

___________________

CUSTOMER ______________________________

________________________

JOB ______________________________________

MACH S/N (PIN) S.M.U.

DEALER

_____________________

APPLICATION ____________________________

_______________________________

SERVICEMAN

LOW PRESSURE STANDBY ___________________

___________________________

RUN ALL TESTS AT MAX. RPM

MARGIN PRESSURE ___________________ MAXIMUM SYSTEM PRESSURE _________________

MACHINE AT NORMAL OPERATING TEMPERATURES

ENGINE LOW IDLE SPEED ___________________ TORQUE LIMITER ENGINE SPEED ___________________

CYCLE TIMES

TEST 1ST Bucket Dump

L O A D E R

(Leveler Off)

Tilt Back (Leveler Off)

Raise (Leveler Off)

Raise (Leveler On, Full Bucker Dump))

Bucket Dump Bucket Load Stick In Stick Out Swing

B A C K H O E

(Stop to Stop)

Swing (Stop to Snubber)

E-Stick Extend E-Stick Retract Left Stab. - Raise Left Stab. - Lower Right Stab. - Raise Right Stab. - Lower Boom Pause Auxiliary 1 Auxiliary 2

Page:

VI-22

2ND

3RD

4TH

AVG.

SPEC

Manual Training Hydraulic System Caterpillar Backhoe Loaders

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