SERV1852-02
August 2008
320D-336D HYDRAULIC EXCAVATORS -
TIER III ENGINES
BOOM, STICK, AND BUCKET CIRCUITS
Service Training Meeting Guide
(STMG)
GLOBAL SERVICE LEARNING
TECHNICAL PRESENTATION
320D-336D HYDRAULIC EXCAVATORS -
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 will
cover 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 be
used 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 hydraulic
excavators, and
2. diagnose problems in the boom, stick, and bucket circuits.
REFERENCES
320D Hydraulic Excavator Specalog AEHQ5856
323D L and 323D LN Hydraulic Excavators HEHH3327
324D Hydraulic Excavator Specalog AEHQ5663
325D Hydraulic Excavator Specalog AEHQ5665

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.
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08/08 Implements
1
INTRODUCTION
This presentation covers in more detail each implement circuit used for the 320D-336D
Hydraulic Excavators. The circuits to be covered include:
- boom
- stick
- bucket
The idler pump provides oil to the boom 2 and stick 1 control valves. The drive pump provides
flow to the bucket, boom 1, and stick 2 control valves.
The boom, stick, and bucket control valves are shifted by pilot oil from the joystick pilot valves
when they are activated.
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.
SERV1852-02 - 5 - Text Reference
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Stick Cylinder
Bucket Cylinder Boom Cylinders
Swing Motor Travel Motors
Pilot

Only one control valve is required to control the bucket. The bucket circuit is supplied with oil
only from the drive pump.
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08/08 Implements
1
2
3
4
5
3
The two joysticks in the cab are used to control the movements of the boom, stick, swing and
bucket 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)
SERV1852-02 - 7 - Text Reference
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1
2
4
Boom Circuit
The boom circuit consists of the following major components:
- boom 1 spool
- boom 2 spool
- 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))

BOOM CIRCUIT COMPONENTS
Boom
Cylinders
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 pilot
signal 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, when
active. The boom 2 spool does not operate during BOOM LOWER. The boom 2 spool has no
provisions 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 boom
will 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 to
unlock 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 more
details 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 at
the same time. The higher the boom pilot pressure to the boom priority valve the less pilot
pressure is available to shift the stick 2 control valve, resulting in more pump flow going to the
boom 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. The
boom lowering control valves prevent boom cylinder drift with valving mounted directly on

Passage
Load
Check
Valve
CONTROL VALVE

NEUTRAL
Port A Port B
Control
Spool
Line Relief
and Makeup
Valve
Pilot
Valve
Pilot
Valve
6
When the boom joystick is moved less than half of the travel distance for BOOM RAISE, low
pilot 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, the
boom 1 control valve opens and the boom 2 control valve remains closed due to the low pilot
pressure.
The drive pump supply oil flows past the boom 1 control valve and unseats the check valve in
the 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 1
control valve.
With the boom valve partially shifted less oil is directed to the NFC relief valve. Less oil to the
NFC relief valve results in a reduced NFC signal to the drive pump. The drive pump control

MAIN HYDRAULIC SYSTEM
BOOM RAISE - SLOW SPEED
NFC
Orifice
Swing
Priority
Valve
Boom
Priority
Valve
7
When the operator begins to move the joystick to shift the boom 1 control valve, metered pilot
pressure causes the control valve to shift slightly.
With the spool initially shifted, the center bypass passage is partially closed. This movement
causes NFC pressure to decrease, which signals the drive pump to begin to upstroke.
The load check valve prevents unexpected implement movements when a joystick is initially
activated at a low pump delivery pressure. The load check valve also prevents oil loss from a
high pressure circuit to a lower pressure circuit.
As the pump supply pressure increases, the load check valve opens to allow pump supply oil in
the parallel feeder passage to flow to the control spool.
The control spool meters pump supply oil to the head ends of the boom cylinders.
SERV1852-02 - 12 - Text Reference
08/08 Implements
Boom
Regen Valve
Boom
Head End
Boom
Rod End
Center

Idler Pump
Pilot Pump
NFC
Orifice
Drift
Reduction
Valve
Pilot Manifold
Heavy Lift
Solenoid
AEC Pressure
Switch
MAIN HYDRAULIC SYSTEM
BOOM RAISE
-
FAST SPEED
Swing
Priority
Valve
Boom
Priority
Valve
9
As the operator moves the joystick farther, the pilot pressure on the end of the spool increases.
The increased pilot pressure causes the boom 1 spool to shift further to the right.
The center bypass passage is now closed, which blocks the oil flow to the NFC signal port on
the right pump control valve. When the NFC signal is reduced, the pump upstrokes and flow is
increased. The increased flow can no longer return to tank through the center 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 parallel

Return oil from the rod end of boom cylinders flows to the boom 1 control valve and then to
the tank. The boom 2 control valve does not handle any of the return flow for the boom circuit.
NOTE: The swing priority valve does not affect the operation of the boom 2 control
valve.
SERV1852-02 - 15 - Text Reference
08/08 Implements
Boom Cylinder
Head End
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
11
During combined operations of BOOM RAISE and STICK IN, the boom raise pilot oil pressure
shifts the pressure reducing valve for the boom priority valve to reduce the stick in pilot
pressure for the stick 2 control valve. With the reduction in stick in pilot pressure to the stick 2
control valve, more pump flow is directed to the boom cylinders during this combined
hydraulic operation.
NOTE: For STICK IN, the stick circuit regeneration valve will shift to direct return oil

Idler Pump
Pilot Pump
NFC
Orifice
Drift
Reduction
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 from
the main pumps to the stick hydraulic circuit decreases. This change causes a greater portion of
the 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 priority
automatically activates when the joystick reaches a certain position during a BOOM RAISE
operation.
The above information describes the condition of BOOM RAISE and STICK IN. During any

Pilot Valve
Boom / Bucket
Pilot Valve
M
Boom 2
Main
Relief
Boom 1
Boom Regen
Valve
Drive Pump
Idler Pump
Pilot Pump
NFC
Orifice
Drift
Reduction
Valve
Pilot Manifold
Heavy Lift
Solenoid
AEC Pressure
Switch
MAIN HYDRAULIC SYSTEM
BOOM LOWER WITH REGENERATION
Swing
Priority
Valve
Boom
Priority

During a slow BOOM DOWN, the low pilot pressure is not able to move the regeneration valve
down so return oil from the the boom cylinder head ends is not able to flow to the boom
cylinder rod ends.
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BOOM REGENERATION VALVE

SLOW BOOM DOWN

A - A
Low Boom Down
Pilot Pressure
AA
Check
Valve
Regen Spool
From Boom
Spool
To Boom
Spool
15
When boom lower pilot pressure increases, the boom regeneration valve is pushed down, a
passage is opened allowing boom head end oil to flow to the check valve. If the boom rod end
pressure is lower than the boom head end oil pressure, then the check valve opens allowing
boom 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 oil
pressure, such as when the boom is being powered down.
SERV1852-02 - 21 - Text Reference
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BOOM REGENERATION VALVE

Line Relief Valve
Shuttle Valve
Boom 2
Boom 1
Manual Bleed
Valve
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
AA
A - A
B - B
B
B
Shuttle
Valve
BOOM DRIFT REDUCTION VALVE


A
B - B
B
B
To Tank
Shuttle
Valve
BOOM DRIFT REDUCTION VALVE

BOOM LOWER
18
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 boom
lowering 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 the
cylinders 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
smooth movement.
SERV1852-02 - 24 - Text Reference
08/08 Implements
1
2

Boom Control
Valve
Tank
Head End
Boom
Down Pilot
Boom
Down Pilot
Boom Control
Valve
Equalization
Passage
Manual
Lower