Manual Training Hydraulic System Caterpillar Backhoe Loaders

Service Training

MALAGA

Backhoe Loaders

Sara

MARCH 1997

VI. HYDRAULIC SYSTEM

1. Load Sensing/Pressure Compensated

2. Hydraulic System - Resolver Network

3. Hydraulic Pump

4. Torque Limiter

5. Steering System

6. Loader Valve Control

7. Backhoe Valve control

CHAPTER : Hydraulic System

BACKHOE LOADERS

VI-1 Page:

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

CHAPTER : Hydraulic System

BACKHOE LOADERS

VI-2

QUIZ

LOAD SENSING/PRESSURE COMPENSATING

TWO VALVE OPERATION

A

CHAPTER : Hydraulic System

BACKHOE LOADERS

QUIZ

2.-If two valves are operated at the same time and at valve A the work port pressure (sig-nal 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

If two valves are operated at the same time and at valve A the work port pressure (sig-nal 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

CHAPTER : Hydraulic System

BACKHOE LOADERS

428C AND 438C BACKHOE LOADER

HYDRAULIC SYSTEM

DUAL TILT CYLINDERS

Hydraulic System Component Checklist

CHAPTER : Hydraulic System

BACKHOE LOADERS

428C, AND 438C BACKHOE LOADERS

HYDRAULIC SYSTEM

DUAL TILT CYLINDERS

STICK END COVER BOOM SWING BUCKET E-STICK LEFT STABILIZER RIGHT STABILIZER PUMP TANK INLET MANIFOLD

CHAPTER : Hydraulic System

BACKHOE LOADERS

428B, AND 438B BACKHOE LOADER HYDRAULIC

SYSTEM

CHAPTER : Hydraulic System

BACKHOE LOADERS

VI-7

Page:

BOOM

SWING

BUCKET

STICK

PRIMARY

RESOLVER

SECONDARY

RESOLVER

LOADER

TILT

LOADER

LIFT

HMU

RIGHT

STABILIZER

LEFT

STABILIZER

TO PUMP CONTROL VALVE

CHAPTER : Hydraulic System

BACKHOE LOADERS

VI-8

_{416B-438B SIGNAL NETWORK}

BOOM

SWING

BUCKET

STICK

PRIMARY

RESOLVER

SECONDARY

RESOLVER

LOADER

TILT

LOADER

LIFT

HAND METERING

UNIT

STABILIZER

STABILIZER

CHAPTER : Hydraulic System

BACKHOE LOADERS

B

D

C

F

A

IMPLEMENT AND STEERING PUMP

LOW PRESSURE STANDBY

E

"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

CHAPTER : Hydraulic System

BACKHOE LOADERS

SIGNAL

PUMP

OUTPUT

LARGE ACTUATOR

SMALL ACTUATOR

AND BIAS SPRING

SWASHPLATE

TORQUE

LIMITER

PRESSURE

CUTOFF

IMPLEMENT AND STEERING PUMP

LOW PRESSURE STANDBY

MARGIN

SPOOL

CHAPTER : Hydraulic System

BACKHOE LOADERS

416B-438B HYDRAULIC PUMP

ENGINE OFF

FLOW

COMPENSATOR

PRESSURE

COMPENSATOR

SIGNAL

PUMP

OUTPUT

LARGE ACTUATOR

SMALL ACTUATOR

& BIAS SPRING

SWASH PLATE

DRIVE

SHAFT

YOKE PAD

PISTON &

BARREL ASSEMBLY

CHAPTER : Hydraulic System

BACKHOE LOADERS

VI-12

TORQUE LIMITER

SIGNAL SIGNAL ADJUSTMENT SCREW SLEEVE SPOOL ACTUATOR PISTON SPRING

NORMAL

REDUCED

FLOW

CHAPTER : Hydraulic System

BACKHOE LOADERS

VI-13

Page:

416B - 438B HYDRAULIC PUMP

TORQUE LIMITER - OPEN

FLOW

COMPENSATOR

PRESSURE

COMPENSATOR

PUMP

OUTPUT

TORQUE

LIMITER

SIGNAL

CHAPTER : Hydraulic System

BACKHOE LOADERS

VI-14 Page:

¥ Torque limiter opera-tion

- Destrokes pump as pressure increases - Spring force varies

with swashplate angle SIGNAL PUMP OUTPUT LARGE ACTUATOR SMALL ACTUATOR AND BIAS SPRING TORQUE

LIMITER MARGIN

SPOOL

IMPLEMENT AND STEERING PUMP

TORQUE LIMITER REDUCES FLOW

PASSAGE TO TANK

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 dis-charge 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 pres-sure 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.

CHAPTER : Hydraulic System

BACKHOE LOADERS

VI-15 Page:

¥ Maintains input torque setting

TORQUE LIMITER

NORMAL

REDUCED

FLOW

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.

CHAPTER : Hydraulic System

BACKHOE LOADERS

VI-16 Page:

¥ Maintains input torque setting

416B - 438B HYDRAULIC PUMP

TORQUE LIMITER - OPEN

FLOW COMPENSATOR PRESSURE COMPENSATOR PUMP OUTPUT TORQUE LIMITER SIGNAL

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 sig-nal line which results in a slight loss of the actual sigsig-nal 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.

CHAPTER : Hydraulic System

BACKHOE LOADERS

E

N

G

I

N

E

R

P

M

TORQUE LIMITER

SETTING

A

B

ENGINE RPM VS. THE TORQUE

LIMITER SETTING

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.

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.

CHAPTER : Hydraulic System

BACKHOE LOADERS

VI-18 Page:

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, maxi-mum 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 adjust-ment 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 cor-rectly.

CHAPTER : Hydraulic System

BACKHOE LOADERS

VI-19 Page:

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.

CHAPTER : Hydraulic System

BACKHOE LOADERS

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 stand-by. When performing the margin pressure test, follow the Service Manual Procedures with the follow-ing 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 pres-sure 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

pres-sure because the steering circuit prespres-sure is below maximum system prespres-sure. 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 differ-ence between the pump supply pressure and the steering signal is margin pressure.

CHAPTER : Hydraulic System

BACKHOE LOADERS

VI-21 Page:

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. Recheck cycle times and margin pressure.

Test One Test Two Test Three Average Cycle time

Margin Pressure

CHAPTER : Hydraulic System

BACKHOE LOADERS

VI-22 Page:

BACKHOE LOADER HYDRAULIC TESTS

DATE _______________________________ DEALER _______________________________ MACHINE MODEL ___________________ CUSTOMER ______________________________ NAME/CODE ________________________ JOB ______________________________________ MACH S/N (PIN) _____________________ APPLICATION ____________________________ S.M.U. _______________________________ SERVICEMAN ___________________________ TEST 4TH AVG. CYCLE TIMES SPEC 1ST 2ND 3RD L O A D E R Bucket Dump (Leveler Off) Tilt Back (Leveler Off) Raise (Leveler Off)

Raise (Leveler On, Full Bucker Dump))

B A C K H O E Bucket Dump Bucket Load Stick In Stick Out Swing (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

RUN ALL TESTS AT MAX. RPM

MACHINE AT NORMAL OPERATING

TEMPERA-TURES

LOW PRESSURE STANDBY___________________

MARGIN PRESSURE ___________________

MAXIMUM SYSTEM PRESSURE _________________

ENGINE LOW IDLE SPEED ___________________