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Caterpillar hydraulic excavators serie D

320D336D HYDRAULIC EXCAVATORS

-TIER III ENGINES

BOOM, STICK, AND BUCKET CIRCUITS

Service Training Meeting Guide

(STMG) GLOBAL SERVICE LEARNING

TECHNICAL PRESENTATION

TIER III ENGINES

BOOM, STICK, AND BUCKET CIRCUITS

AUDIENCE

Level II - Service personnel who understand the principles of machine systems operation,diagnostic equipment, and procedures for testing and adjusting

CONTENT

This presentation provides an introduction and describes the components and systems operation

of the 320D-336D implement circuits - boom, stick, and bucket Additional presentations willcover the machine walkaround, engines, pilot system, main control valve group, implements,swing system, travel system, and tool control systems in more detail This presentation may beused for self-paced and self-directed training

OBJECTIVES

After learning the information in this presentation, the technician will be able to:

1 identify the correct operation of the boom, stick, and bucket on the 320D-336D hydraulicexcavators, and

2 diagnose problems in the boom, stick, and bucket circuits

REFERENCES

Self-study "300D Series Hydraulic Excavators, 345C Hydraulic Excavator,

Estimated Time: 1 1/2 Hours

Illustrations: 44

Form: SERV1852-02

Date: August 2008

© 2008 Caterpillar

TABLE OF CONTENTS

INTRODUCTION 5

Boom Circuit 8

Stick Circuit .34

Bucket Circuit 52

Cylinders 53

CONCLUSION 55

NOTES

Nomenclature Change: During the fourth quarter of 2008, the 325D and 330D

nomenclature changed The 325D became the 329D and the 330D became the 336D for most arrangements.

The exceptions are as follows:

- The nomenclature for the 325D MH and 330D MH did not change.

- The nomenclature for the 325D FM and 330D FM did not change.

- The 325D HD HW did not change into 329D HD HW This model is being discontinued However, the 330D HD HW changed to the 336D HD HW.

INTRODUCTION

This presentation covers in more detail each implement circuit used for the 320D-336D

Hydraulic Excavators The circuits to be covered include:

NOTE: The main control valve group and return system are covered in another

presentation The attachment/auxiliary circuits will be covered in the electronic or tool control section The ISO schematics were created primarily from "325D Hydraulic

Schematic" (KENR6157) Hydraulic schematics for other 320D-336D excavators

may/will have variations from illustrations shown.

Stick Cylinder

Bucket Cylinder Boom Cylinders

Pilot

Control

Valves

Priority Valves

Main Hydraulic

Pilot Pump Fan

Motor

Pilot Manifold

Main Control Valve Group

Fan Pump Tank

The Fan Motor and Pump are only used on the 330D and 336D IMPLEMENT CIRCUITS

The boom circuit uses two control valves to control the boom operation, boom 1 (1) and boom

2 (2) Both spools shift when fast boom movement is required Both pumps provide flow tothe boom for this condition Boom 1 valve provides single pump flow, whenever the boom isshifted for slow movement

The stick circuit also uses to two control valves to control the stick operation, stick 1 (3) andstick 2 (4) Both spools shift when fast stick movement is required

The boom circuit and stick circuits also use regeneration valves and drift reduction valves Theregeneration valves (not shown) provide improved efficiency and require less engine

horsepower for BOOM LOWER and STICK IN

The drift reduction valves reduce cylinder drift when the boom or stick are in NEUTRAL

Only one control valve is required to control the bucket The bucket circuit is supplied with oilonly from the drive pump

1

2

3 4

5

The two joysticks in the cab are used to control the movements of the boom, stick, swing andbucket circuits

- right joystick (1) to control the bucket and boom (SAE excavator pattern)

- left joystick (2) to control the swing and stick (SAE excavator pattern)

1 2

- two boom cylinders

- drift reduction valve

- Heavy Lift solenoid

- boom priority valve (pressure reducing)

- boom lowering control valves (if equipped - not shown))

- boom regeneration valve

- SmartBoom™ (if equipped - not shown))

NOTE: 325D Hydraulic Schematic (KENR6157) was used to develop the ISO

Boom 1

Boom Regen Valve

Pilot Manifold

Heavy Lift Solenoid

AEC Pressure

Switch

MAIN HYDRAULIC SYSTEM

BOOM CIRCUIT COMPONENTS Cylinders Boom

Boom Priority Valve

Boom 1 Spool: The boom 1 spool controls oil flow from the drive pump The boom 1 spool

receives a BOOM RAISE pilot signal on the bottom of the valve, and a BOOM LOWER pilotsignal on the top of the valve

Boom 2 Spool: The boom 2 spool controls oil flow from the idler pump The boom 2 spool

receives a BOOM RAISE pilot signal from the joystick on the top of the valve stem, whenactive The boom 2 spool does not operate during BOOM LOWER The boom 2 spool has noprovisions for return oil from the boom cylinders

Boom Cylinders: The boom cylinders work in parallel to control the raise and lower

movement of the boom When oil is supplied to the head end of the boom cylinders, the boomwill raise When oil is supplied to the rod end of the boom cylinders, the boom will lower

Boom Drift Reduction Valve: The boom drift reduction valve prevents oil from leaking from

the head end of the boom cylinders For BOOM LOWER, pilot oil from the joystick is used tounlock the lock check valve in the drift reduction valve

Heavy Lift Solenoid: The heavy lift solenoid is activated to increase the maximum system

pressure for lifting (Refer to the "Main Control Valve Group and Return Group" for moredetails on Heavy Lift operation.)

Boom Priority Valve: The boom priority valve (pressure reducing) is used to reduce the pilot

pressure to the stick 2 valve whenever both the BOOM RAISE and STICK IN are activated atthe same time The higher the boom pilot pressure to the boom priority valve the less pilotpressure is available to shift the stick 2 control valve, resulting in more pump flow going to theboom cylinders

Boom Lowering Control Valves: The boom lowering control valves are infinitely variable,

pilot operated control valves that control the movement of the boom during lowering Theboom lowering control valves prevent boom cylinder drift with valving mounted directly oneach of the boom cylinders, that controls boom cylinder head end oil flow

Because the valves are mounted directly to each of the boom cylinders, the boom loweringcontrol valves will prevent the boom from falling, even if a hose becomes defective from themain control valve to the cylinders

The boom lowering control valves also work in conjunction with the SmartBoom™ system tocontrol the boom with the function active

Regeneration Valve: The regeneration valve allows return oil from the head end of the boom

cylinders to be directed into the rod end of the cylinders when the boom is lowered fast

SmartBoom™: The SmartBoom™ attachment enhances operation of the boom function and

significantly reduces cycle times of the machine The SmartBoom™ is essentially a boom floatattachment, which allows the operator to lower the boom under its own weight or for the boom

to raise up due to stick force The SmartBoom™ attachment is typically used in EAME

As previously discussed, the control valve operation is similar for all of the valves in the maincontrol valve group including the boom, stick, and bucket valves Pump flow is provided bythe drive and/or idler hydraulic pump Which pump is used depends on the circuit

The centering spring force holds the valve spool to NEUTRAL when there is no pilot oil

pressure directed to shift the spool

In NEUTRAL the valve spool allows oil to flow unrestricted through the center bypass passage,which directs a high NFC pressure signal to the pump control valve The high NFC pressurecauses the pump to destroke to a standby condition, as explained previously

Parallel

Feeder

Passage

Center Bypass Passage

Line Relief and Makeup Valve

Pilot

When the boom joystick is moved less than half of the travel distance for BOOM RAISE, lowpilot oil pressure is supplied to the boom 1 control valve and the boom 2 control valve

The force of the centering spring in the boom 1 control valve is less than the force of the

centering spring in the boom 2 control valve When the boom is raised at a low speed, theboom 1 control valve opens and the boom 2 control valve remains closed due to the low pilotpressure

The drive pump supply oil flows past the boom 1 control valve and unseats the check valve inthe drift reduction valve and flows to the head end of the boom cylinders

Return oil from the rod end of the boom cylinders returns back to the tank through the boom 1control valve

With the boom valve partially shifted less oil is directed to the NFC relief valve Less oil to theNFC relief valve results in a reduced NFC signal to the drive pump The drive pump controlvalve causes the pump to upstroke to provide flow to operate the boom

A BOOM RAISE operation at low speed is accomplished when only the drive pump is supplied

to the head end of the boom cylinders

Swing / Stick

Boom 2

Main Relief

Boom Regen Valve

Pilot Manifold

Heavy Lift Solenoid

AEC Pressure

Switch

MAIN HYDRAULIC SYSTEM

BOOM RAISE - SLOW SPEED

NFC Orifice

Swing Priority Valve

Boom Priority Valve

As the pump supply pressure increases, the load check valve opens to allow pump supply oil inthe parallel feeder passage to flow to the control spool.

The control spool meters pump supply oil to the head ends of the boom cylinders

Boom Regen Valve

Boom Head End Rod End Boom

BOOM 1 CONTROL VALVE

BOOM RAISE PARTIAL SHIFT

Boom 1

Boom Regen Valve

Pilot Manifold

Heavy Lift Solenoid

AEC Pressure

Switch

MAIN HYDRAULIC SYSTEM

BOOM RAISE - FAST SPEED

Swing Priority Valve

Boom Priority Valve

The increased oil flow to the parallel feeder passage causes pressure to rise in the parallelfeeder passage The increased oil pressure overcomes the force of the load check spring andthe boom head end pressure, which causes the load check valve to unseat Oil flows out toboom cylinders

The oil returning from the rod end of the cylinders flows past the spool and returns to tank

NFC Signal

Boom Head End

Boom Rod End

BOOM 1 CONTROL VALVE

BOOM RAISE FULL SHIFT

Swing Priority

Pressure

Reducing Valve

Variable Swing Priority Valve

Parallel Feeder

Passage

Center Bypass

Passage

BOOM 2 CONTROL VALVE

FAST BOOM RAISE

Load Check Valve

Control Spool

NOTE: For STICK IN, the stick circuit regeneration valve will shift to direct return oil

from the rod end of the stick cylinder to the head end of the cylinders

When the joystick for the stick is moved to the STICK IN position, a portion of the pilot oilfrom the pilot control valve for the stick flows through the pressure reducing valve for theboom priority to the stick 2 control valve As the joystick for the boom is moved farther for aBOOM RAISE, pilot oil pressure from the pilot control valve for the boom increases Thisgradual increase in pilot oil pressure causes the spool in the pressure reducing valve for theboom priority to gradually shift

A portion of the pilot oil to the stick 2 control valve from the stick pilot control valve is

restricted by the boom priority valve The pilot oil pressure acting on the stick 2 control valvedecreases

Stick Unloading

Valve

Main Relief

Boom Regen Valve

Pilot Manifold

Heavy Lift Solenoid

AEC Pressure

Switch

MAIN HYDRAULIC SYSTEM

BOOM PRIORITY - BOOM RAISE AND STICK IN

Swing Priority Valve

Boom Priority Valve

The stick 2 control valve shifts toward the NEUTRAL position The amount of oil flow fromthe main pumps to the stick hydraulic circuit decreases This change causes a greater portion ofthe oil flow from the main pumps to flow to the head end of the boom cylinders.

Since the pilot oil pressure from the boom pilot control valve directly corresponds to the

amount of movement or position of the boom joystick a gradual change to boom priority

occurs

Thus, boom priority is controlled by the position of the joystick for the boom and boom priorityautomatically activates when the joystick reaches a certain position during a BOOM RAISEoperation

The above information describes the condition of BOOM RAISE and STICK IN During anycombined function of BOOM RAISE and STICK IN, the pressure reducing valve for boompriority reduces pilot pressure to the stick 2 control valve

NOTE: If the joysticks are fully shifted for BOOM RAISE and STICK IN, stick in pilot

pressure on the bottom of the boom 2 cancels the boom raise pilot pressure on top of the boom 2 spool At the same time the boom priority valve prevents stick in pilot pressure from going to the stick 2 control valve.

These two actions result in the drive pump supplying oil to the boom cylinders and the idler pump providing oil to the stick cylinder.

For BOOM LOWER only the boom 1 control valve is used The drive pump partially strokes

to provide flow to the rod end of the boom cylinders

When the joystick is shifted pilot oil moves the boom 1 control spool down, the regenerationvalve right, and unlocks the drift reduction valve When the boom 1 control spool is fullyshifted, the center bypass valve is never fully closed off By not closing off the center passage,there is an NFC signal to the drive pump The drive pump never fully upstrokes

Due to the force of gravity, with the lock valve unlocked, the weight of the boom and the load

on the boom, force the return oil out of the cylinder head ends back to the regeneration valveand the boom 1 control valve

The boom 1 control valve restricts the return oil flow Whenever the return oil pressure ishigher than the supply pressure in the rod end of the cylinders, the return oil from the boomcylinder head ends unseats the check valve above the regeneration valve

The return oil from the head end enters the supply passage to the rod end to help fill the

cylinders and prevent cylinder cavitation The regeneration valve allows the excavator tooperate more efficiently The main pump supply oil not required to lower the boom is available

to operate another circuit

Swing / Stick

Boom 2

Main Relief

Boom 1

Boom Regen Valve

Pilot Manifold

Heavy Lift Solenoid

AEC Pressure

Switch

MAIN HYDRAULIC SYSTEM

BOOM LOWER WITH REGENERATION

Swing Priority Valve

Boom Priority Valve

The boom pilot oil flow from shifts the boom control spool to the left against the force of thecentering spring Supply oil from the drive pump in the parallel feeder passage flows past theload check valve to the rod end of the boom cylinders

Some of the oil in the center bypass passage flows past the center land to provide a reducedNFC signal The reduced NFC signal causes the drive pump to only partially upstroke

Part of the return oil from the head end of boom cylinders flows to the boom drift reductionvalve

Rod End Head End

NFC Signal

BOOM 1 CONTROL VALVE

BOOM LOWER

cylinder rod ends.

BOOM REGENERATION VALVE

SLOW BOOM DOWN

Regen Spool

From Boom Spool

To Boom Spool

When boom lower pilot pressure increases, the boom regeneration valve is pushed down, apassage is opened allowing boom head end oil to flow to the check valve If the boom rod endpressure is lower than the boom head end oil pressure, then the check valve opens allowingboom head end oil to be directed to the boom rod end

The check valve closes if the boom rod end oil pressure is higher than the boom head end oilpressure, such as when the boom is being powered down

BOOM REGENERATION VALVE

FAST BOOM DOWN

Regen Spool

From Boom Spool

To Boom Spool

Boom Drift Reduction Valve: The boom drift reduction valve prevents oil from leaking from

the head end of the boom cylinders The boom drift reduction valve is located on the maincontrol valve group The boom drift reduction valve has the following components:

- shuttle valve

- lock check valve

- line relief valve

In NEUTRAL, the shuttle valve and check valve are closed by spring force Oil is blockedbetween the boom control valve and the boom cylinders

For BOOM RAISE, the shuttle valve is closed by spring force When closed, the shuttle valveallows oil from the boom control valves to act on one end of the lock check valve

Oil pressure from the boom control valves acts on the other end of the lock check valve Thelock check valve opens (due to pressure differential on check valve) to allow oil flow to the rodend of the boom cylinders

Line Relief Valve

From Boom 1 And Boom 2 Control Valves

Shuttle Valve

Line Relief Valve

Check Valve

Lock Check Valve

To Boom Cylinders Head End

BOOM DRIFT REDUCTION VALVE

BOOM RAISE

Line Relief Valve

To Boom 1 Control Valve

Shuttle Valve

Line Relief Valve

Check Valve

Check Valve

From Boom Cylinders Head End

BOOM DRIFT REDUCTION VALVE

BOOM LOWER

Boom Lowering Control Valves: The boom lowering control valves (1 and 2) are mounted on

the head end of the boom cylinders If the machines are equipped with the optional boomlowering valves, the drift reduction valve for the boom is not installed on the machine

The boom lowering control valves serve several purposes:

- prevent the boom from falling rapidly in case of hose failure

- provide BOOM LOWER control with SmartBoom™ (if equipped) activated

- prevent boom drift

The lowering control valves are equipped with head end line relief valves (3) to protect thecylinders from sudden shocks

A pilot line (4) directs pilot oil to unlock the lowering control valve so the boom can be

lowered

The tube (5) provides supply oil from the boom control valve

A hose (6) connects both lowering control valves The line provides for equalization of

pressures in the head end of the cylinders when the boom is raised or lowered to provide

When the boom circuit is equipped with boom lowering control valves (or load control valves),the lowering control valves are attached directly to each of the boom cylinders

The following major components are used in the boom lowering control valves :

- boom head end line relief

BOOM LOWERING CONTROL VALVE

NEUTRAL

Boom Control Valve Tank

Head End

Boom Down Pilot

Boom Head End Line Relief: The boom head end line relief protects the boom head end

circuit from damage if the pressure in the circuit exceeds the line relief setting

Check Valve: The check valve holds the high pressure of the boom cylinder head end

from leaking off Because the weight of the boom, stick, and work tool are always applied

to the head end of the boom cylinder, the check valve is needed to prevent the high

pressure from leaking off and allowing the boom to drift The check valve also provides

an unrestricted means for the high pressure/high flow oil from the main control valve toenter the boom cylinder head end during BOOM UP

Boom Lowering Control Valve Spool: The infinitely variable boom lowering control

valve spool controls the flow of oil exiting the boom cylinder head end The top of thespool receives pilot pressure from the boom lower joystick When the valve opens, oilflows from the head end back to the main control valve Because the valve is infinitelyvariable and controlled by boom lower pilot pressure, the speed that the boom lowers iscontrolled by the boom lowering control valve spool

Orifice: The boom lowering control valves on each cylinder are connected by a small

hose The hose ensures that pressure is always equal in the two cylinders The orifice ineach of the boom lowering control valves restricts the amount of oil that flows from onecylinder to the other The restriction created by the orifice will allow control over theboom in the event that the hose ruptures Under normal operation the orifice plays no role

in boom operation

Manual Lower: Manual lower allows the boom to be lowered if the engine will not run.

The valve allows the oil pressure in the head end of the cylinder to bleed to the tank

NEUTRAL: When no boom function is performed the boom lowering control valve is in

NEUTRAL In NEUTRAL no oil flows to or from the boom cylinders, and the boom does notmove

In NEUTRAL, the check valve is seated by the combination of the spring force and the highpressure oil in the head end of the boom cylinders The boom lowering control valve spool isseated by spring force

The boom lowering control valves have no effect on the flow of oil to/from the rod end of theboom cylinders

NOTE: Manual lower may be done differently depending on the lowering control

valves used Some machines may have a manual lowering valve separate from the

lowering control valves.

The schematic above shows the two lowering control valves and the boom circuit controlvalves in NEUTRAL

Both pumps are destroked

NOTE: The stick circuit may also be equipped with a single lowering control valve.

Operation of the stick lowering control valve will be similar With only a single stick cylinder there is no need for an equalization passage.

Boom 1 Spool

Boom 2 Spool

BOOM CIRCUIT WITH LOWERING

CONTROL VALVES

NEUTRAL

Boom Up Pilot

Boom Lowering Control Valve

Boom Regen Valve

Boom Rod End Line Relief Valve

Straight Travel

Main Relief

Pilot Oil

Heavy Lift Solenoid

Boom Down Pilot

M

Drive Idler Pump