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Caterpillar hydraulic excavators serie D

320D336D HYDRAULIC EXCAVATORS

-TIER III ENGINES

MAIN CONTROL VALVE GROUP AND RETURN

TIER III ENGINES

MAIN CONTROL VALVE GROUP AND RETURN

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

of the 320D-336D main control valve group and return system Additional presentations willcover the machine walkaround, engines, pilot system, pumps and controls, swing system, travelsystem, and tool control systems in more detail This presentation may be used for self-pacedand self-directed training

OBJECTIVES

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

1 identify the components and explain the operation of the 320D-336D hydraulic

excavators main control valve group and return system, and

2 diagnose problems in the main control valve group and return system

REFERENCES

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

iTIM " '300C' Series Hydraulic Excavators-Electronic Control Systems" SERV2693iTIM "325C Hydraulic Excavators-Hydraulic Systems" SERV2701

Estimated Time: 1 Hour

Illustrations: 22

Form: SERV1852-02

Date: August 2008

© 2008 Caterpillar

TABLE OF CONTENTS

INTRODUCTION 5

Main Control Valve Group 6

Additional Components .15

Return Hydraulic System 24

CONCLUSION 29

"Fundamentals of Mobile Hydraulics Self Study Course" TEMV3002

"Fundamentals of Power Train Self Study Course" TEMV3003

"Fundamentals of Electrical Systems Self Study Course" TEMV3004

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

The main hydraulic system is a Negative Flow Control (NFC) System that supplies hydraulicpower at high pressures and high flow rates to perform work Two main hydraulic pumpssupply oil to the main control valve group The individual hydraulic circuits are controlled byvalves in the the main control valve group

The main hydraulic system supplies the following circuits:

Main Hydraulic Pumps M

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

Main Control Valve Group

The main control valve group is located in the center of the upper structure of the machine.The main control valve group receives pilot oil signals from the operator controls in the cab.Each pilot signal then causes the appropriate control valve to shift in the correct direction

When a control valve shifts, oil flows from the main hydraulic pumps to the appropriate

hydraulic cylinder or hydraulic motor to perform work The medium 320D-336D main controlvalve is similar to the medium 300C Series valve The components shown above include:

- right side NFC relief valve (1) - main relief valve (8)

- right travel (6) - auxiliary valve for tool control (13)

- straight travel valve (7)

The pilot-operated, open-center control valves are of parallel feeder design Because the maincontrol valve group uses the open-center portion of the control valve to generate a NFC signalfor the pumps, the oil must have another path to deliver oil to the work ports This is

accomplished through a parallel feeder path A parallel feeder path runs parallel to the

open-center path and supplies oil to the work port of each implement valve

When all of the joysticks and pedals are in the NEUTRAL position, drive pump oil flows

through the right pump inlet port to the right half of the main control valve group In the righthalf of the main control valve group the oil flows two directions; to the center bypass passages,and to the parallel feeder passages

Stick 2

Boom 1 Attach

Right Travel

Left Travel Swing

Stick 1

Boom 2

Drive Pump Inlet Port

Return Passage

Center Bypass Passage

Idler Pump Inlet Port

NFC Orifice Straight Travel

Valve

Bucket

NFC Signal Pressure for Drive Pump

The oil in the center bypass passages flows in series through the center bypass passage of thetravel, the attachment, the bucket, the boom 1, and the stick 2 valves to the NFC control orifice.The NFC control orifice allows the oil to return to tank with a restriction

This restriction provides an NFC signal pressure which is sent to the drive pump to maintainthe drive pump at minimum angle when the control valves are all in NEUTRAL In

NEUTRAL this NFC signal is the same as the supply pressure

The oil in the parallel feeder passage flows in parallel to the attachment, the bucket, the

boom 1, and the stick 2 valves Since all of the valves are in NEUTRAL, the oil in the parallelfeeder is blocked by the valve spools, and all oil must flow through the center bypass to thetank

The oil from the idler pump flows similarly through the left half of the control valve when allvalves are in NEUTRAL

Since the control valves are in NEUTRAL the supply oil flows through all of the valves to thetank Some of this oil becomes NFC signal oil and destrokes the two pumps.

Swing PRV

M

Bucket Valve Boom 2

Stick 1

Stick Regen Valve

Stick Unloading

Valve

Swing Left Travel

Straight Travel

Main Relief

Variable Swing Priority Valve

Straight Travel Solenoid Attachment Valve

Right Travel

Line Relief and Makeup Valve

Boom 1 Stick 2

Boom Regen Valve

NFC

Relief

Valve

NFC Relief Valve

Drive Pump Idler Pump

Pilot Pump

NFC Signal

Line (Idler Pump)

NFC Signal Line (Drive Pump)

NFC

Orifice

Pilot Oil

Heavy Lift Solenoid

MAIN CONTROL VALVE GROUP NEGATIVE FLOW CONTROL OPERATION - NEUTRAL

Drift Reduction Valve Parallel Feeder

Passage

Parallel Feeder Passage

Control valve operation is similar for all of the valves in the main control valve group Thefollowing explanation is for the basic operation of all of the valves in the main control valvegroup The variations in each individual valve will be discussed later in more detail

The control valve above is shown in NEUTRAL

The valve spool is spring centered in NEUTRAL when there is no pilot oil pressure directed toshift the spool In the NEUTRAL position, the spool blocks the oil in Port A and Port B

Oil flows from the pump to the parallel feeder passage The load check valve is seated because

of the pressure differential and spring force present on the load check valve

In NEUTRAL, the valve spool allows oil to flow unrestricted through the center bypass

passage, which directs a high NFC signal pressure to the pump control valve The high NFCsignal pressure causes the pump to destroke to a standby condition

Parallel

Feeder

Passage

Center Bypass Passage

Line Relief and Makeup Valve

Pilot

Load Check Valve

Centering Spring Full NFC

Signal

Pilot Valve

CONTROL VALVE

INITIAL MOVEMENT

Reduced NFC Signal

When the operator begins to move the joystick to shift the control valve, metered pilot pressurecauses the control valve to shift slightly

With the spool initially shifted, the center bypass passage begins to close This movementcauses NFC signal pressure to decrease, which causes the pump to begin to upstroke

The movement of the spool partially opens a passage allowing the oil from Port B to work withthe load check valve spring to keep the load check valve seated

The load check valve prevents unexpected implement movements when a joystick is initiallyactivated at a low pump supply pressure The load check valve also prevents oil loss from ahigh pressure circuit to a lower pressure circuit

The combined force of the work port pressure from Port B and the force of the spring above theload check is greater than the pump supply pressure, causing the load check valve to remainclosed

As the operator moves the joystick for a full shift, the pilot pressure on the end of the spoolincreases This increased pilot pressure causes the spool to fully shift

The center bypass passage is fully closed, which blocks the oil flow to the NFC signal passage

to the pump control valve When the NFC signal pressure is fully reduced, the pump fullyupstrokes and flow is increased The increased flow can no longer return to tank through thecenter bypass passage All oil now flows through the parallel feeder path

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 workport pressure in Port B, which causes the load check valve to unseat Oil flows out toPort B

The oil returning from Port A flows past the spool and returns to tank

NOTE: The load check valve is a loose fit in the load check seat to allow leakage past

the check valve from the spring chamber A separate spring chamber vent passage is

not required with this load check design.

Pilot Valve

Reduced NFC Signal

of the idler pump is decreased to STANDBY due to the increased NFC pressure.

The bucket control spool is fully shifted by pilot oil when the joystick is fully moved Flowfrom the drive pump flows into the right side of the main control valve and into the centerbypass passage to the bucket control valve Because the bucket control spool is fully shifted,all of the oil flow from the drive pump flows to the bucket cylinder No oil flows to the NFCcontrol orifice and no NFC signal pressure is generated Because no NFC signal pressure flows

to the pump control valve, the pump control valve moves the pump toward maximum angle.The drive pump flow output increases to maximum

The individual circuits of the main control valve group will be covered in more detail later

Swing PRV

M

Bucket Valve Boom 2

Stick 1

Stick Regen Valve

Stick Unloading

Valve

Swing Left Travel

Straight Travel

Main Relief

Variable Swing Priority Valve

Straight Travel Solenoid Attachment Valve Right Travel

Line Relief and Makeup Valve

Boom 1 Stick 2

Boom Regen Valve

NFC

Relief

Valve

NFC Relief Valve

Drive Pump Idler Pump

Pilot Pump

NFC Signal Line (Idler Pump)

NFC Signal Line (Drive Pump)

NFC

Orifice

Pilot Oil

Heavy Lift Solenoid

MAIN CONTROL VALVE GROUP NEGATIVE FLOW CONTROL OPERATION - CONTROL VALVE SHIFTED

Drift Reduction Valve

Parallel Feeder Passage

Parallel Feeder Passage

When the joystick is partially moved from the NEUTRAL position to perform a fine controloperation, reduced pilot pressure shifts the control spool slightly to the left The movement ofthe control spool partially opens a passage to Port B

The movement of the control spool also partially blocks the center bypass passage, whichdivides the flow from the one drive into two flow paths A portion of the pump output flowsthrough the center bypass passage to the NFC orifice at a reduced pressure The remainder ofthe drive pump output flows through the parallel feeder passage and internal passages to Port B

Because the oil flow from the center passage to the NFC orifice decreases, the NFC signalpressure to the drive pump control valve decreases The reduced NFC signal causes the drivepump to move toward maximum angle The drive pump output increases proportional to thereduction in NFC signal pressure

Pilot Valve

CONTROL VALVE

FINE CONTROL

Reduced NFC Signal

10 Additional Components

The main relief valve (1) is located in the left half of the main control valve group The mainrelief valve limits the maximum operating pressure of the the travel and implement hydrauliccircuits For the NACD market the 300D Series main relief valve has two settings Onesetting is for the standard maximum pressure and the other setting is for Heavy Lift In allother markets Heavy Lift is optional

When energized the heavy lift solenoid (not shown) sends a pilot signal through the line (2) atthe top of the relief valve to increase the pressure setting of the main relief valve

When heavy lift is selected, the Machine ECM limits engine speed to speed dial 6 and activatesthe heavy lift solenoid The heavy lift solenoid directs pilot oil to the main relief valve toincrease the relief valve setting At the same time the Machine ECM increases the power shiftpressure to decrease the pump output flow Decreasing the pump output flow provides

increased controlability and hydraulic smoothness during a heavy lift operation

The Heavy Lift Mode limits the pumps to a maximum of approximately 60% of the normalhydraulic horsepower Heavy Lift Specs:

- Engine rpm for Heavy Lift is the engine speed dial 6 setting

- Hydraulic horsepower is limited to 60% of full power during Heavy Lift

- Main relief maximum pressure during Heavy Lift is 36000 kPa ± 490 kPa

(5225 ± 70 psi)

1

2

Heavy lift is activated by pressing the heavy lift switch (1) on the soft switch panel (2) in theoperators station The heavy lift switch is an input to the Machine ECM

The heavy lift solenoid (3) is located near the hydraulic tank and below the main control valvegroup

11

12

3

1 2

Pilot Oil

Heavy Lift Solenoid

E

Idler Pump Drive Pump

Main Control Valve

Straight Travel

Control Valve

Travel Control Valve

Main Relief Valve

Center Bypass Right

Parallel Feeder Right

Main Relief Valve

Straight Travel Control Valve

Drive Pump

Idler Pump

Check Valves

Parallel Feeder Left

Center Bypass Right Parallel Feeder Right

Pilot Oil

Straight Travel Solenoid

Center Bypass Left

The drive pump oil flow enters the main control valve group through the upper delivery line.The idler pump oil flow enters the main control valve group through the lower delivery line.The drive pump oil and idler pump oil pressures work against the two check valves

The oil from both pumps is directed to the appropriate passages by the straight travel valve

The check valves ensure that only the higher pressure from the idler or the drive pump flows tothe main relief valve The check valves also ensure that flow from the highest supply pressurecircuit does not enter the other supply pressure circuit if the pressure is lower

For example, if the bucket was being closed at a high pressure and no other function was active,the lower check valve would close The check valve would prevent the drive pump oil fromflowing through the center bypass in the left circuit This action ensures that the higher supplypressure is always sensed at the relief valve

The relief valve will open when a circuit is stalled, limiting the maximum system pressure

unloading spool down.

As the system pressure nears the main relief valve pressure setting, the force of the systempressure in the lower spring chamber overcomes the force of the upper spring This causes thepoppet to unseat, allowing system oil to flow around the poppet to the return passage As theoil in the lower spring chamber flows around the poppet, additional system pressure oil flowsthrough the orifice into the lower spring chamber at a reduced pressure

System pressure overcomes the force of the oil pressure in the lower spring chamber and thespring, causing the unloading spool to move upward As the unloading spool moves upward,system pressure oil is allowed to flow to the return passage

Pilot Oil

Heavy Lift Solenoid

Piston

Pump Supply

HEAVY LIFT ON

Spindle Lock Nut

Lock Nut

Adjustment Nut

Pilot Oil

Heavy Lift Solenoid

Pump Supply

HEAVY LIFT OFF

Poppet Unloading

Spool Orifice

Pilot Oil

Heavy Lift Solenoid

CLOSED OPEN CLOSED

MAIN RELIEF VALVE