SERV1852-02
August 2008

GLOBAL SERVICE LEARNING
TECHNICAL PRESENTATION

320D-336D HYDRAULIC EXCAVATORS TIER III ENGINES
SWING SYSTEM

Service Training Meeting Guide
(STMG)


320D-336D HYDRAULIC EXCAVATORS TIER III ENGINES
SWING SYSTEM
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 swing system. 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 selfdirected training.

OBJECTIVES
After learning the information in this presentation, the technician will be able to:
1. identify the correct operation of the swing system on the 320D-336D hydraulic
excavators, and
2. diagnose problems in the swing system.

REFERENCES
320D Hydraulic Excavator Specalog
323D L and 323D LN Hydraulic Excavators
324D Hydraulic Excavator Specalog
325D Hydraulic Excavator Specalog
328D Hydraulic Excavator Specalog
330D Hydraulic Excavator Specalog
Machine Monitoring System - Systems Operation
Self-study "300D Series Hydraulic Excavators, 345C Hydraulic Excavator,
and 365C & 385C Large Hydraulic Excavators
iTIM " '300C' Series Hydraulic Excavators-Electronic Control Systems"
iTIM "325C Hydraulic Excavators-Hydraulic Systems"
325D Hydraulic Schematic

Estimated Time: 1 Hour
Illustrations: 32
Form: SERV1852-02
Date: August 2008
© 2008 Caterpillar

AEHQ5856
HEHH3327
AEHQ5663
AEHQ5665
AEHQ5706
AEHQ5667
RENR8068
SERV7032
SERV2693
SERV2701

KENR6157


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Text Reference
Swing System

TABLE OF CONTENTS
INTRODUCTION ........................................................................................................................5
Swing System Components ....................................................................................................6
Swing System Operation ......................................................................................................11
Swing Motor Operation ........................................................................................................18
Swing Drive ..........................................................................................................................34
CONCLUSION ..........................................................................................................................39


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Text Reference
Swing System

PREREQUISITES
"Fundamentals of Mobile Hydraulics Self Study Course"

"Fundamentals of Power Train Self Study Course"
"Fundamentals of Electrical Systems Self Study Course"
"Fundamentals of Engines Self Study Course"

TEMV3002
TEMV3003
TEMV3004
TEMV3001

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.


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Text Reference
Swing System

SWING SYSTEM
Stick Cylinder

Bucket Cylinder
Swing Motor

Main Control Valve Group

Pilot
Control
Valves

Priority
Valves

Pilot Manifold

Pilot
Pump
Fan
Motor

Boom Cylinders

Travel Motors

Main
Hydraulic
Pumps

M
Fan
Pump


Tank

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

1

INTRODUCTION
This presentation covers the 320D-336D swing system. The swing system includes the
following components:
- swing control valve (part of the main control valve group)
- swing motor
- variable swing priority valve (part of the swing control valve)
- swing priority valve
- dual stage, swing line relief valves
- cushion crossover anti-reaction valves
- fine swing control solenoid valve (not available in EAME after October 2008)
- swing brake
- slow return check valve
The idler pump supplies flow for the swing system. The swing control valve is shifted by pilot
oil from the joystick pilot valves.


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Swing
Brake


Swing Motor
Group

Text Reference
Swing System

SWING SYSTEM

Motor
Line Relief
Valve

SWING COMPONENTS - NEUTRAL

Makeup
Valve

Anti-Reaction
Valves

Fine Swing
Valve

Swing / Stick
Pilot Valve

Out

In


R

Variable
Swing
Priority
Valve

Swing
Control
Valve
Stick 2
Control
Valve

L

Idler
Pump

M
Drive
Pump

Swing Priority
Pressure Reducing
Valve

AEC Pressure
Switch


Swing
Brake
Solenoid

Slow Return
Check Valve

Pilot
Pump

Hydraulic
Activation
Valve

Implement
Hydraulic
Lockout
Solenoid

Pilot
Manifold

2

Swing System Components
The swing circuit controls the rotation of the swing motor. The idler pump provides the pump
flow for the swing circuit.
When either one of the joysticks is moved from the NEUTRAL position, the swing parking
brake is released. The swing motor is mounted on top of the swing drive. The swing drive is

installed on the upper structure and rotates the upper structure.
When the hydraulic activation control lever is in the UNLOCKED position, pilot pump oil
flows to the swing parking brake solenoid valve in the pilot manifold and to the swing pilot
control valve. Pilot oil from the pump also flows through the swing priority pressure reducing
valve to the variable swing priority valve and moves the variable swing priority valve fully up.
With the swing control valve in NEUTRAL, pump supply oil from the idler pump flows though
the center bypass valve of the swing control valve and all other control valves shown to the
NFC valve. The return oil creates a signal used to destroke the idler pump.


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Text Reference
Swing System

The swing brake is currently on so the motor will not rotate.
Since the implement hydraulic lockout solenoid has been energized, the hydraulic activation
valve has shifted. Pilot oil is directed to the pilot joystick and to the swing brake solenoid.
Swing Priority Pressure Reducing Valve and Variable Swing Priority Valve: These two
valves work together to provide flow priority over the stick control valve when the stick and
swing are operated together.
Swing Parking Brake Solenoid Valve: When energized the swing parking brake solenoid
valve directs pilot oil to release the swing parking brake. The solenoid will energize when
either one of the joysticks is moved from the NEUTRAL position.
Dual Stage, Swing Relief Valves: These relief valves limit the maximum pressure in the left
and right swing circuits. The dual stage, swing relief valves open initially at a lower pressure
to reduce jerkiness in the swing circuits at swing start and swing stop or to handle short

duration pressure spikes. The relief valves also allow for higher swing circuit pressures to
provide increased swing force.
NOTE: The ISO symbol shown on the schematics does not reflect that the relief valves
are dual stage.
Slow Return Check Valve: The back pressure created by the slow return check valve ensures
that makeup oil is available at the swing motor and the various makeup valves in the hydraulic
system.
Anti-reaction or Cushion Relief Valves: These valves dampen pressure spikes in the swing
system whenever the swing is stopped. The valves also inhibit counter rotation of the swing
motor when the swing is stopped, which reduces swing "wag." The valves also provide for a
smooth swing start-up.
Fine Swing Control Solenoid Valve: When energized the fine swing control solenoid valve
improves the swing control during swing deceleration. This solenoid valve helps to reduce the
shock when the swing stops by connecting the supply and the return sides of the motor so the
pressures between the two sides begin to equalize.


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Text Reference
Swing System

3
1

3


2

4
4

The swing system uses one control valve (1) in the main control valve group (2) to control the
swing operation.
The slow return check valve is part of the slow return check valve and cooler bypass manifold
group (3).
The left joystick (4) in the cab is used to control the direction and speed of the swing.


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4

Text Reference
Swing System

1

2

5

3


6
7
5
6

The swing control valve directs oil to and from the swing motor (1). Additional swing motor
components shown are the:
- swing brake release pressure line (2)
- swing drive oil level dipstick (3)
- crossover relief valve (4)
- anti-reaction valve group (5)
- anti-reaction valve (6) (one of two)
- fine swing control solenoid valve (7)


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Text Reference
Swing System

1
2
7

4
3


5

8

The swing brake solenoid valve (1) is part of the pilot manifold (2). The manifold is located
directly below the main control valve. The hydraulic activation solenoid (3) must energize to
shift the hydraulic activation valve (4). If the hydraulic activation valve is not shifted there is
no pilot oil to the swing brake solenoid valve. The swing brake can not be released.
There is also no pilot oil available to the joystick pilot valves if the hydraulic activation valve is
not shifted.
The swing priority pressure reducing valve (5) is located beneath the main control valve group.
The variable swing priority valve (not shown) is located on the main control valve group near
the boom 2 spool.


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Text Reference
Swing System

SWING CONTROL VALVE
NEUTRAL

Port A

Port B


Load
Check
Valve

Parallel
Feeder
Passage

Center
Bypass
Passage

9

Swing System Operation
The swing control valve operates as previously discussed.
Line relief and makeup valves for the swing circuit are located in the swing motor instead of
the swing control valve.


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Swing
Brake

Swing Motor
Group


Text Reference
Swing System

SWING SYSTEM

Motor

FULL SWING LEFT

Line Relief
Valve
Makeup
Valve

Anti-Reaction
Valves

Fine Swing
Valve

Left Travel
Control
Valve

Swing / Stick
Pilot Valve

Out


In

R

Stick 1
Control
Valve

Variable
Swing
Priority
Valve

Swing
Control
Valve
Stick 2
Control
Valve

L

Idler
Pump

M
Drive
Pump

Swing Priority

Pressure Reducing
Valve

AEC Pressure
Switch

Swing
Brake
Solenoid

Pilot
Pump

Hydraulic
Activation
Valve

Slow Return
Check Valve

Implement
Hydraulic
Lockout
Solenoid

Pilot
Manifold

10


When the swing joystick is full shifted, pilot oil from the swing joystick flows to the swing
control valve to shift the control spool. The control valve shifts and blocks the oil in the center
passage from flowing to the idler pump. The idler pump fully upstrokes.
At the same time, the AEC switch closes due to sensing pilot pressure from swing pilot valve.
The Machine ECM senses the switch is closed and energizes the swing brake solenoid.
The swing brake solenoid directs pilot oil to release the swing brake.
The load check valve unseats and supply oil from the pump is directed to the swing motor. The
anti-reaction valves cushion the start of the swing motor. Return oil from the motor flows past
the swing control valve to the tank.
Also, when the swing joystick is fully shifted, the swing pilot oil acts on the swing priority
pressure reducing valve. The pressure reducing valve shifts to block the pilot oil to the variable
swing priority valve and opens a passage for the pilot oil at the variable swing priority valve to
flow to tank. The spring above the variable swing priority valve moves the valve fully down.
In the illustration above, swing is the only circuit in operation.


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Swing
Brake

Swing Motor
Group

Text Reference
Swing System


SWING SYSTEM

Motor
Line Relief
Valve

PARTIAL SWING LEFT / NO PRIORITY OVER STICK

Makeup
Valve

Stick
Cylinder

Stick 2
Control Valve

Anti-Reaction
Valves
Fine Swing
Valve
Left Travel
Control
Valve

Swing / Stick
Pilot Valve

Out


In

R

Stick 1
Control
Valve

Variable
Swing
Priority
Valve

Swing
Control
Valve
Stick 2
Control
Valve

L

Idler
Pump

M
Drive
Pump

Swing Priority

Pressure Reducing
Valve

AEC Pressure
Switch

Swing
Brake
Solenoid

Pilot
Pump

Hydraulic
Activation
Valve

Slow Return
Check Valve

Implement
Hydraulic
Lockout
Solenoid

Pilot
Manifold

11


The swing pilot oil pressure from the swing pilot control valve directly corresponds to the
amount of movement or position of the swing joystick. The swing pilot oil pressure from the
pilot control valve acts on the swing priority pressure reducing valve.
When the swing pilot pressure and the downstream pressure to the variable swing priority valve
is less than the the spring setting of the swing priority pressure reducing valve, the swing
priority pressure reducing valve does not shift.
The variable swing priority valve is held up to the load check valve position by the pilot oil
pressure from the pilot manifold.
If the stick 1 circuit is being operated at the same time as a partial swing, flow from the idler
pump unseats the load check valve section of the variable swing priority valve and is directed to
the stick cylinder.
The stick cylinder speed is determined by how far the stick spool shifts.
The stick 2 control valve also shifts for a full stick out. The stick 2 control valve is not affected
by the variable swing priority valve.


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Text Reference
Swing System

SWING PRIORITY PRESSURE REDUCING VALVE
AND VARIABLE SWING PRIORITY VALVE
NO SWING PRIORITY - STICK 1 FULLY SHIFTED

Boom Up
Pilot Valve

Stick In
Pilot Valve
B1

Stick 2
Stick In
Pilot

Swing
Pilot Valve

Pilot
Manifold

Stick 1
Supply

Variable Swing
Priority Valve

B2

P1

P2

A1

A2


Load Check
Valve

Swing Priority Pressure
Reducing Valve

Center Pump
Parallel Feeder
Supply Passage
Passage

Boom 2
Control Valve

12

For a partial SWING, the pilot pressure oil from the pilot manifold and from the swing pilot
valve cannot overcome the swing priority pressure reducing valve spring to move the valve
down.
Full pilot oil pressure from the pilot manifold is maintained on the variable swing priority
valve.
Pilot oil to the variable swing priority valve moves the valve up against the spring above the
valve.
With the variable priority valve held up, the swing priority valve does not restrict oil to the
stick 1 control valve.
The load check valve will unseat when the idler pump supply pressure in the parallel feeder
passages exceeds the stick workport pressure.
Unrestricted flow from the idler pump is available to the stick 1 control valve to operate the
stick.



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Swing
Brake

Swing Motor
Group

Text Reference
Swing System

SWING SYSTEM

Motor
Line Relief
Valve

FULL SWING LEFT / PRIORITY OVER STICK

Makeup
Valve

Stick 2
Control Valve
Anti-Reaction
Valves

Fine Swing
Valve
Left Travel
Control
Valve

Swing / Stick
Pilot Valve

Out

In

R

Stick 1
Control
Valve

Variable
Swing
Priority
Valve

Swing
Control
Valve
Stick 2
Control
Valve


L

Idler
Pump

M
Drive
Pump

Swing Priority
Pressure Reducing
Valve

AEC Pressure
Switch

Swing
Brake
Solenoid

Slow Return
Check Valve

Pilot
Pump

Hydraulic
Activation
Valve


Implement
Hydraulic
Lockout
Solenoid

Pilot
Manifold

13

As the swing joystick is moved farther from the NEUTRAL position, the pilot oil pressure
increases.
This gradual increase in pilot oil pressure causes a gradual change to the swing priority pressure
reducing valve. The pressure reducing valve shifts and starts to restrict more of the pilot oil
from the pilot manifold to the variable swing priority valve. For a full swing the pilot oil is
blocked and the passage to the variable swing priority valve is drained to the tank.
As the pilot oil to the variable swing priority valve is reduced, the valve moves down and
begins to restrict the idler pump flow to the stick circuit through the stick 1 control valve for
STICK OUT.
The stick slows down. The further the swing joystick is shifted, the more the stick cylinder
slows for a STICK OUT. The stick 2 control valve will fully shift and direct available drive
pump flow to the stick cylinder.
The maximum flow to the stick for STICK UP is limited by the position of the variable swing
priority valve and not by how far the stick 1 spool has shifted.


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Text Reference
Swing System

Swing priority is controlled by the position of the swing joystick. Swing priority over the stick
is hydraulically activated when the swing joystick reaches a certain position.
For STICK IN, the stick 1 control valve shifts. Due to the regeneration valve (not shown), the
stick in speed is not affected unless the stick has reached the vertical position and the stick
unloading valve is open. Without swing priority, during a full STICK IN, the stick circuit
would receive most if not all of the idler pump flow.
NOTE: The focus of this story is on the effect of the swing priority valve over the stick
circuit. For a STICK IN, there may also be flow from the stick 1 valve unless the boom
1 valve has shifted for BOOM UP.
Since swing priority increases the swing acceleration whenever the stick is also used, swing
priority is useful for loading operations. Swing priority is also useful for leveling operations
and trenching operations when higher swing force is required.


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Text Reference
Swing System

SWING PRIORITY PRESSURE REDUCING VALVE
AND VARIABLE SWING PRIORITY VALVE
SWING PRIORITY ACTIVATED


Boom Up
Pilot
Swing
Pilot

Stick In
Pilot
B1

Stick 2
Stick In
Pilot

B2

Variable Swing
Priority Valve
Spring

P1

P2

A1

A2

Boom Priority
Pressure Reducing

Valve

Stick 1
Supply

Pilot
System

Swing Priority
Pressure Reducing
Valve

Load Check
Valve

Restriction

Center Pump
Parallel Feeder
Supply Passage
Passage

Boom 2
Control Valve

14

When the swing pilot valve is fully shifted, the swing priority pressure reducing valve is moved
down to completely drain the pilot oil to the variable swing priority valve to the tank.
The variable swing priority valve moves down due to spring force.

With the variable swing priority valve held down, supply oil to the stick 1 control valve is
restricted.
The stick cylinder speed is reduced.


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Pilot Oil Supply

- 18 -

Text Reference
Swing System

Swing
Parking
Brake

SWING MOTOR

SECTIONAL VIEW - SWING RIGHT
Slow Return
Check Valve

Crossover Relief
Valve

Piston and
Barrel Assembly


Makeup
Valve

Separator
Plate

Drive
Shaft
Spring
Tank Passage to
Slow Return Check Valve

Swing Control
Valve

Swing Brake
Piston

Friction
Plate

Shoes

15

Swing Motor Operation
The swing motor may be divided into the following three groups :
- the rotary group: piston and barrel assembly, shoes, retainer plate, and drive shaft
- the parking brake: brake spring, brake piston, separator plates, and friction plates

- the relief valves and makeup valves
When a swing operation is started, pilot oil from the swing brake solenoid valve is directed to
the swing brake piston. As the pilot pressure builds, the brake piston moves against the spring
to release the swing brake. The brake separator plates and friction plates are no longer in
contact and the motor barrel assembly can rotate freely.
During a SWING RIGHT operation, the oil delivery enters the motor head from the swing
control valve and flows through a plate in the motor into the piston and barrel assembly to
cause the motor to rotate.
Return oil flows back from the motor to the motor head and back to the swing control valve to
return to the tank.


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Text Reference
Swing System

SWING
PARKING BRAKE
OFF

Swing Parking
Brake Spring
Swing Brake
Piston

Swing Brake

Solenoid Valve
Spring

Pilot
Oil

Separator
Plate

Spool

Friction Plate

Barrel

16

The swing parking brake is located in the swing motor. The swing parking brake consists of
the following components: brake spring, brake piston, separator plates, and friction plates. The
friction plates are splined to the cylinder barrel. The separator plates are splined to the motor
case.
When the joysticks are moved from the NEUTRAL position, the implement/swing (AEC)
pressure switch senses the increase in pilot oil pressure. The pressure switch closes and sends
an input signal to the Machine ECM. The Machine ECM then energizes the swing brake
solenoid valve.
When the swing brake solenoid valve is energized, the spool moves down against the spring.
Pilot oil flows to the center of the spool and out to the swing motor.
The pilot oil now enters the piston chamber. The pilot pressure causes the brake piston to move
upward against the force of the brake spring. The separator plates and friction plates are no
longer held together and the motor is able to rotate freely.



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Text Reference
Swing System

SWING
PARKING BRAKE
ON

Parking Brake
Spring
Swing Brake
Piston

Swing Brake
Solenoid Valve
Spring

Pilot
Oil

Separator
Plate

Spool


Friction Plate

Barrel

17

When the joysticks are returned to the NEUTRAL position, idler pump supply oil to the swing
motor is stopped. The implement/swing pressure (AEC) switch senses the decrease in pilot oil
pressure. The implement/swing pressure switch opens. The Machine ECM senses the change
in state of the implement/swing pressure switch and de-energizes the swing brake solenoid
valve.
The spool is moved upward by the force of the spring in the solenoid valve. The spool blocks
pilot oil flow from flowing to the brake piston. Oil in the brake piston is open to the tank
through the swing brake spool.
The parking brake spring moves the brake piston down to press the separator plates and friction
plates together to apply the swing parking brake.
Since the Machine ECM does not de-energize the swing brake solenoid valve until
approximately 6.5 seconds after the swing joystick is returned to the NEUTRAL position, the
rotation of the swing motors stops hydraulically before the swing brake is engaged.
If the solenoid is de-energized before the rotation of the swing motors stops, damage and wear
to the swing parking brake would result.