Hệ thống thủy lực máy đào CATERPILLAR SERIE D - P5

SERV1852-02
August 2008

GLOBAL SERVICE LEARNING
TECHNICAL PRESENTATION

320D-336D HYDRAULIC EXCAVATORS TIER III ENGINES
MAIN HYDRAULIC PUMPS AND PUMP CONTROL
VALVE GROUPS

Service Training Meeting Guide
(STMG)


320D-336D HYDRAULIC EXCAVATORS TIER III ENGINES
MAIN HYDRAULIC PUMPS AND PUMP CONTROL
VALVE GROUPS
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 main hydraulic pumps and pump control valve groups. 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 components and explain the operation of the 320D-336D hydraulic

excavators main hydraulic pumps and controls, and
2. diagnose problems in the main hydraulic pumps and controls.

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: 22
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
Main Pumps

TABLE OF CONTENTS
INTRODUCTION ........................................................................................................................5
320D - 329D MAIN HYDRAULIC PUMP GROUP ................................................................11
Pump Control Valve Group ..................................................................................................16
330D / 336D MAIN HYDRAULIC PUMP GROUP ................................................................21
Pump Control Valve Group ..................................................................................................27
CONCLUSION...........................................................................................................................36


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Text Reference
Main Pumps

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
Main Pumps

MAIN HYDRAULIC PUMPS AND PUMP CONTROL VALVE GROUPS
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 section of the presentation will cover the main hydraulic pumps and pump controls for the
300D Hydraulic Excavators.
The main pump group consists of a variable displacement piston drive pump and a variable
displacement piston idler pump. The drive pump and the idler pump are part of an integral
housing. The drive pump and the idler pump are identical in construction and operation.
The pumps are sometimes referred to as S.B.S. (side by side) pumps. The main difference
between all of the pumps is the maximum pump flow for each model.
Both the drive pump and the idler pump have individual pump control valve groups to control
the pump flow.
The 320D through the 329D use the same type of pump control valve group. The 330D/336D
pump control valve group is the same as the pump control valve group used on the 345C pump.


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Text Reference

Main Pumps

POWER SHIFT PRESSURE
SYSTEM
Idler
Pump

Pump Control
Valve
Power Shift
PRV Solenoid

Engine Speed
Sensor

Drive
Pump

Output
Pressure
Sensor

Engine
ECM

Machine
ECM

Pilot
Pump

Engine
Speed Dial

Monitor

OK

2

Power shift pressure is controlled by the Machine ECM, and assists in pump regulation. Power
shift pressure is one of three pressures to control the pump.
The pilot pump supplies the power shift PRV solenoid with pilot oil. The Machine ECM
monitors the selected engine speed (from the engine speed dial), the actual engine speed (from
the engine speed sensor and Engine ECM), and the pump output pressures (from the output
pressure sensors). The power shift PRV solenoid valve regulates the pressure of the power shift
oil depending upon the signal from the Machine ECM to the pump control valve groups.
When the engine speed dial is in position 10, the Machine ECM varies the power shift pressure
in relation to the actual speed of the engine.
The power shift pressure is set to specific fixed values dependent upon the position of the
engine speed dial. The fixed power shift pressures assist cross sensing pressure (not shown)
with constant horsepower control.


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Text Reference

Main Pumps

When the engine speed dial is on position 10 and a hydraulic load is placed on the engine, this
condition causes the engine speed to decrease below the engine's target rpm.
When this decrease occurs, the Machine ECM signals the power shift PRV solenoid valve to
send increased power shift pressure to the pump control valve groups. The increased power
shift signal causes the pumps to destroke, and reduce the horsepower demand placed on the
engine. With a decreased load from the hydraulic pumps the engine speed increases. This
function is referred to as engine underspeed control.
Engine underspeed control prevents the engine from going into a "stall" condition where engine
horsepower cannot meet the demands of the hydraulic pumps. The power shift signal to the
pump control valve groups enables the machine to maintain a desired or target engine speed for
maximum productivity.
Power shift pressure has the following effect on the main hydraulic pumps:
- As power shift pressure decreases, pump output increases.
- As power shift pressure increases, pump output decreases.
Power shift pressure ensures that the pumps can use all of the available engine horsepower for
the hydraulic system at all times without exceeding the output of the engine.
NOTE: The target rpm is the full load speed for a specific engine "no load" rpm.
Engine target rpm is determined by the opening of one of the implement, swing, and/or
travel pressure switches at the end of an operation. The Machine ECM then waits 2.5
seconds and records the engine speed. This specific rpm is the "new" no load rpm.
The Machine ECM then controls the power shift pressure to regulate pump flow to
maintain the full load (target) rpm for the recorded no load rpm.
Target rpm can change each time the pressure switches open for more than 2.5 seconds.


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Text Reference
Main Pumps

PROPORTIONAL REDUCING
SOLENOID VALVE
PWM SIGNAL INCREASE

Solenoid

Plunger
Spring

Tank
Power Shift Pressure
Pilot Pressure

3

The proportional reducing solenoid valve (PRV) for the power shift pressure is located on the
drive pump control valve group. The proportional reducing solenoid valve receives supply oil
from the pilot pump.
The solenoid receives a pulse width modulated signal (PWM signal) from the Machine ECM.
The PWM signal sent from the Machine ECM causes the proportional reducing solenoid valve
to regulate the pilot pressure to the pump control valve groups to a reduced pressure.
This reduced pressure is called power shift pressure (PS).
The output flow of the drive pump and the idler pump is controlled in accordance with the
power shift pressure. The power shift pressure is used to control the maximum hydraulic pump
output in relation to the engine rpm.

A decrease in engine speed causes an increase in power shift pressure and a decrease in pump
flow.


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Text Reference
Main Pumps

When the speed dial is at dial position 10, if the Machine ECM senses a decrease in engine
speed below target rpm, the Machine ECM increases the PWM signal sent to the solenoid.
The magnetic force of the solenoid increases. As the magnetic force of the solenoid becomes
greater than the force of the spring, the spool moves down against the force of the spring.
The downward movement of the spool blocks the flow of oil to the tank.
More power shift pressure oil is now directed to the pump control valve group.
The increased power shift pressure acts on the drive pump control valve group and the idler
pump control valve group.
If both pumps are upstroked, then both pumps will destroke as a result of the increase in power
shift pressure. If only one pump is upstroked, only the upstroked pump will destroke.


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Text Reference

Main Pumps

PROPORTIONAL REDUCING
SOLENOID VALVE
PWM SIGNAL DECREASE

Solenoid

Plunger
Spring

Tank
Power Shift Pressure
Pilot Pressure

4

If engine speed is above the target rpm, the Machine ECM decreases the power shift pressure to
increase the pump flow.
When the Machine ECM senses an increase in engine speed above the target speed the Machine
ECM decreases the PWM signal sent to the proportional reducing solenoid valve.
As the magnetic force of the proportional reducing solenoid valve becomes less than the force
of the spring, the spool moves up.
The upward movement of the spool restricts the pilot oil flow to the power shift passage and
opens the power shift passage to the drain. The power shift pressure is reduced.
The reduced power shift pressure acts on the drive pump control valve group and the idler
pump control valve group.
Depending on which circuits are activated, the drive pump and/or the idler pump will upstroke
as a result of a decrease in power shift pressure.

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Text Reference
Main Pumps

3
5
4

1
6

2

5

320D - 329D MAIN HYDRAULIC PUMP GROUP
This illustration shows the main hydraulic pumps groups. The drive pump (1) is driven by the
engine and the idler pump (2) is driven by the drive pump. The pilot pump (3) is mounted on
the drive pump. The medium pressure pump (4) is driven by the idler pump.
The drive pump supplies oil to the right half of the main control valve group and the following
valves:
- stick 2 control valve
- boom 1 control valve
- bucket control valve
- attachment control valve

- right travel control valve


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Text Reference
Main Pumps

The idler pump supplies oil to the left half of the main control valve group and the following
valves:
- left travel control valve
- swing control valve
- stick 1 control valve
- boom 2 control valve
- auxiliary valve for tool control (if equipped)
The output of the variable-displacement piston pumps is controlled by the pump control valve
groups (5 and 6) mounted on the main hydraulic pumps.


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Text Reference
Main Pumps

5

1

6

3

4

2

6
This illustration shows the pump control valve group for the drive pump. Except for the power
shift solenoid, the components for the idler pump are identical.
The power shift PRV solenoid valve (1) provides a common power shift pressure for both
pumps. The power shift PRV solenoid valve is controlled by the Machine ECM.
The pump output pressure sensors (2) signals the Machine ECM of each pump's output
pressure. The Machine ECM uses the pump output pressure, actual engine speed, and desired
engine speed to determine the power shift pressure. The pressure sensors also signal the
Machine ECM to cancel the AEC settings if the pump pressure increases above approximately
7370 kPa (1100 psi) and the engine rpm is still at an AEC setting.
The horsepower adjusting screws (3) adjust the hydraulic horsepower output of each pump.
The maximum angle screw (4) limits the maximum flow of each pump.
The pressure tap (5) above the power shift PRV solenoid valve can be used to check the PRV
signal pressure. The pressure tap (6) just above the pressure sensor can be used to check the
drive pump supply pressure. Another pressure tap (not shown) can be used to check the idler
pump supply pressure. Cat ET can also be used to check these two pressures.

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MAIN PUMP GROUP
U

STANDBY

Text Reference
Main Pumps
Medium Pressure
Circuit

M2

Pump Control Valve

Main Control Valve
Group (Left Side)

Left NFC
Control
Orifice
PS2
Idler
Pump

Cross

Sensing
Orifice

Med Press
Pump
Pilot
Pump

M
Drive
Pump

Case Drain

Actuator

Power Shift
PRV Solenoid
Valve
Main Control Valve
Group (Right Side)
M1
Output
Pressure Sensor
U

Pilot Filter and
Manifold

Right NFC

Control
Orifice

Pilot Pump

7
This illustration shows the pumps in STANDBY condition.
The pump control valve groups will upstroke, destroke, or maintain the displacement of the
pump depending on the conditions the pump control valve group senses. The pump control
valve group controls oil pressure (stroking pressure) to the right side of the actuator, which
controls the angle of the pump swashplate.
Each pump has a pump control valve group which senses the three following control signals:
- a pump specific Negative Flow Control (NFC) signal from the main control valve group
- a common power shift signal pressure generated by the power shift PRV
- a common cross sensing signal pressure from the output of the two main pumps
NFC: NFC pressure is the most significant controlling signal in a negative flow controlled
hydraulic system. Each pump control valve group receives a specific NFC signal that is based
upon the hydraulic demand for that specific pump.


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Text Reference
Main Pumps

Flow from the drive pump supplies the right half of the main control valve group and has a
corresponding NFC signal for the drive pump. Flow from the idler pump supplies the left half

of the main control valve group and has a corresponding NFC signal for the idler pump.
The open-center valves in the main control valve group allow pump output to flow through
unrestricted. An orifice in the NFC valve creates a restriction to the pump output which
increase the NFC pressure. The NFC pressure then signals the corresponding pump control
valve group. Each pump will remain at STANDBY as long as a full NFC signal pressure is
present.
When a hydraulic control valve is shifted from the NEUTRAL position, the NFC signal
pressure to the corresponding pump is reduced, which causes the pump to UPSTROKE. Any
change in the movement of a valve in the main control valve group will effect the NFC signal
because the valves send a variable NFC signal to the pump depending on the needed pump
output.
Output of each pump is unaffected by a change in the NFC signal to the other pump. NFC
pressure has the following effect on the main hydraulic pumps:
- As NFC pressure decreases, pump output increases,
- As NFC pressure increases, pump output decreases.
NFC signal pressure overrides all other control of the main hydraulic pumps.
Cross Sensing: Cross sensing pressure is essentially an average pressure from the output of
the drive pump and the idler pump.
The output of each pump flows respectively to the left and right halves of the main control
valve group. The output of each pump also flows to the cross sensing orifices.
The cross sensing pressure compensates for the horsepower demand of each pump individually
and for the two pumps together. With cross sensing assistance, the pumps constantly regulate
the flow to effectively use all of the available engine horsepower at any given time. This
regulation is referred to as constant horsepower control.
Cross sensing pressure has the following effect on the main hydraulic pumps:
- As cross sensing pressure decreases, pump output increases,
- As cross sensing pressure increases, pump output decreases.
Given a fixed NFC signal, cross sensing signal pressure regulates the output of the main
hydraulic pumps.
NOTE: Hydraulic horsepower is a function of pump output flow and pressure. As

pump flow or pressure increases, the horsepower demand increases. As pump flow or
pressure decreases, the horsepower demand decreases.


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Text Reference
Main Pumps

MAIN PUMP CONTROL VALVE GROUP
STANDBY

D

Pin A

Actuator

D
Actuator
Pivot

Cross Sensing
Signal

Control
Linkage

Power Shift
Signal
NFC

Pin A

Control
Signal
Pivot

Pin B

Guide
Horsepower
Control Spool

Sleeve

Pin B

Shoulder

Pilot
Control

Control
Piston

Swashplate

SECTION D-D

8
Pump Control Valve Group
The above illustration shows a cross sectional view of one of the main hydraulic pump control
valve groups in STANDBY. The main pumps will be in STANDBY condition when the engine
is running and all control valves are in NEUTRAL. Under these conditions the NFC pressure
signal to the pump control valve groups is high. The pump can not upstroke until NFC signal
pressure is reduced.
The high NFC signal pressure causes the NFC control piston to move left against the force of
the NFC spring on the right. When the NFC control piston moves left the piston contacts the
shoulder on the pilot piston, which causes the pilot piston to move the horsepower control spool
against the spring force on the left end of the valve.
The passage between horsepower control spool and the sleeve is now open to tank, causing the
right end of the actuator to be open to the tank. The actuator moves to the right, moving the
swashplate to a minimum angle, which causes pump output flow to be minimum.
NOTE: With S.B.S. pumps, system pressure at STANDBY (maximum NFC signal)
destrokes the pumps to minimum. When the pump is upstroked all three signals work
together to control the angle of the pump swashplate to regulate the pump flow.


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Text Reference
Main Pumps

MAIN PUMP CONTROL VALVE GROUP

UPSTROKED - NFC SIGNAL REDUCED

D

Pin A

Actuator

D
Actuator
Pivot

Cross Sensing
Signal

Control
Linkage

Power Shift
Signal
NFC

Pin A

Control
Signal
Pivot

Pin B

Guide
Horsepower
Control Spool

Sleeve

Pin B

Shoulder

Pilot
Control

Control
Piston

Swashplate
SECTION D-D

9
The pumps must have a reduction in NFC pressure to upstroke from STANDBY. The
illustration shows the pump control valve groups upstroking the pump due to a decrease in NFC
signal pressure. As shown, there is no NFC signal pressure, indicating that at least one control
valve has been fully shifted.
When one of the joysticks or travel levers is moved from the NEUTRAL position, NFC signal
pressure decreases proportionally to the amount the joystick or travel lever is moved. When the
NFC signal pressure decreases, the spring on the control piston forces the control piston to the
right. The horsepower control springs on the left overcome the cross sensing signal pressure
and the power shift signal pressure to move the horsepower control spool to the right.
With the horsepower control spool shifted to the right, the passages between the sleeve and the

horsepower control spool are closed off to tank and pump output pressure is allowed to flow to
the right side of the actuator. Because the right side of the actuator is larger than the left side,
the greater force generated by the pressure on the right side causes the actuator to move left to
upstroke the pump.
The pump can also be upstroked by a decrease in either power shift or cross sensing pressure,
but only after a reduction in NFC pressure has caused the pump to move from the minimum
angle.


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Text Reference
Main Pumps

MAIN PUMP CONTROL VALVE GROUP
CONSTANT FLOW

D

Pin A

Actuator

D
Actuator
Pivot

Cross Sensing
Signal

Control
Linkage

Power Shift
Signal
NFC

Pin A

Control
Signal
Pivot

Pin B

Guide
Horsepower
Control Spool

Sleeve

Pin B

Shoulder

Pilot
Control

Control
Piston

Swashplate
SECTION D-D

10

As the pump upstrokes, the movement of the actuator causes the control linkage to move the
sleeve around the horsepower control spool. The sleeve moves to the right as the actuator
moves to the left. Because of the geometry of the control linkage, a large movement of the
actuator moves the sleeve a small amount (see Section D-D).
The small movement of the sleeve causes the passages between the sleeve and the horsepower
control spool to open partially to the tank and partially to the pump output. The pressure signal
sent to the right side of the actuator is now metered, which causes the actuator to reach a
balance point where the pump does not upstroke or destroke. With the actuator at a fixed
position the swashplate angle of the pump is fixed. Constant flow is now achieved.
Due to varying loading and operating conditions, this fixed output is rarely maintained for very
long. When operating conditions change, the pump will UPSTROKE or DESTROKE.


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Text Reference
Main Pumps

MAIN PUMP CONTROL VALVE GROUP
DESTROKE

D

Pin A

Actuator

D
Actuator
Pivot

Cross Sensing
Signal

Control
Linkage

Power Shift
Signal
NFC

Pin A

Control
Signal
Pivot

Pin B

Guide
Horsepower
Control Spool

Sleeve Pin B

Shoulder

Pilot
Control

Control
Piston

Swashplate
SECTION D-D

11

The three things which can cause the pumps to DESTROKE are:
- an increase in NFC pressure
- an increase in cross sensing pressure
- in increase in power shift pressure
This illustration shows the system under a heavy hydraulic load. As the supply pressure
increases due to the heavy load, the cross sensing signal pressure rises as an average of the left
and right pump delivery pressures. The cross sensing signal acts on the difference of the two
areas on the pilot piston. As the cross sensing signal increases, the pilot piston moves to the
left, which pushes the horsepower control spool left against the force of the horsepower control
springs on the left.

As the spool moves left, the large end of the actuator is opened to tank by a passage between
the horsepower control spool and the sleeve. The pressure decreases on the right end of the
actuator and the actuator moves to the right, which causes the pump to DESTROKE.


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Text Reference
Main Pumps

An increase in power shift signal pressure has a similar effect as an increase in cross sensing
signal pressure. If the hydraulic pump lugs the engine below full load speed, the Machine
ECM increases the current to the power shift PRV solenoid valve. The increased signal causes
a higher power shift signal to be sent to the pump control valve groups.
The power shift pressure acts on the right side of the pilot piston. The force generated from the
power shift pressure assists cross sensing pressure to destroke the pump. As the pump
destrokes the engine speed will increase due to the reduction in load.
An increase in NFC signal pressure will cause the pump to destroke. If all control valves were
returned to NEUTRAL, the NFC signal causes the pump to fully destroke and return to
STANDBY.


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6

Text Reference
Main Pumps

8
5

4

7
1
9

10

2

3

12

330D /336D MAIN HYDRAULIC PUMP GROUP
The 330D and the 336D uses a new Kawasaki designed main hydraulic pump group (1) rated at
2 x 280 L/Min (2 x 74 gpm). The pump group is different from the pump group used on the
330C, however it continues to use an NFC control system. This pump group is similar to the
pump group used on the 345C.
The drive pump (2) is driven by the engine via a flexible coupling. The idler pump (3) is
driven directly off the drive pump. Each pump rotating group has its own pump control valve
group. The pump control valve groups are used to adjust the output flow of the pumps. Each

pump rotating group also has its own pressure tap and pressure sensor.
A power shift PRV solenoid valve (4) is mounted on the top, center of the pump group case.
The power shift PRV solenoid valve uses pilot system oil and sends some of the pilot oil to the
main hydraulic pump control valve groups as a control signal pressure. The power shift
pressure is checked at pressure tap (5).
Additional pump components shown in this photo are: the drive pump control valve group (6),
the idler pump swashplate minimum angle adjustment (7) and the idler pump control valve
group (8). The pilot pump (9) is driven off the idler pump and the demand fan pump (10) is
driven off of the drive pump.


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Text Reference
Main Pumps

2

1

13

This is a view of the drive pump pump control valve group. The pump control valve group is
located above and behind the power shift PRV solenoid valve. This illustration shows:
- the drive pump negative flow control adjustment (1)
- the drive pump horsepower control adjustment (2)
The idler pump control valve group has similar adjustment screws.

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Text Reference
Main Pumps

330D / 336D PUMP COMPONENTS AND INPUTS
Right NFC Control Orifice

Horsepower
Control Spool

Drive Pump Cross
Sensing Signal

Torque Control
Spool

Idler Pump Cross
Sensing Signal

NFC Spool

Drive Pump Output
Pressure Sensor
Actuator

P

Destroke
Main Control Valve
(Right Side)

Drive
Pump

M

Pilot Pump

Pilot
Pump

Power
Shift (PRV)
Solenoid Valve

Idler
Pump

14

Each pump receives four different signals to control the output flow of the pumps:
- power shift pressure
- system pressure from that pump
- cross sensing pressure (from the other pump)

- Negative Flow Control (NFC) pressure
Power Shift Pressure: The power shift PRV receives a control signal from the ECM. The
ECM sends an electrical signal to the power shift PRV to regulate power shift pressure in
relation to the engine speed.
The power shift signal to the pump control valve groups enables the machine to maintain the
target engine speed for maximum productivity.


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Text Reference
Main Pumps

If the Machine ECM senses that the engine is below the target speed due to a high hydraulic
load from the main pumps, the Machine ECM will increase the power shift pressure. The
target speed is the full load for the no load engine speed. (The new no load speed is taken 2.5
seconds after the implement/swing and the travel pressure switches open when the joysticks
and the travel control pilot controls are returned to NEUTRAL). As power shift pressure
increases, the pump control valve groups destroke the main pumps accordingly. This reduces
the load on the engine, and consequently enables the engine to maintain the target engine
speed.
If the engine speed is above the target speed, the Machine ECM will decrease power shift
pressure, causing the pumps to upstroke and produce more flow.
Cross sensing Control Pressure: Each pump control valve group gets a cross sensing control
pressure from the other pump system pressure. Cross sensing pressure is essentially an average
pressure from the output of the drive pump and the idler pump.
Negative Flow Control (NFC): NFC is the primary controlling signal for the main pump

output. The NFC signal to the main pump control valve group is generated in the main control
valve group. The NFC signal is delivered to the left and right pump control valve groups from
the left and right halves of the main control valve group, respectively.
When the joysticks or travel levers are in the NEUTRAL position, the oil flows from the main
pumps through the open center bypass passages of the control valves. The oil flows to the
valves and returns to the tank by way of the NFC control orifices. The restriction of the NFC
orifices causes a pressure signal to be sent to the right and left pump control valve groups,
respectively, as an NFC signal.
When the main pump control valve groups receive a high NFC signal from the main control
valves, the pumps remain at a standby output flow at or near minimum pump displacement.
When a joystick or travel lever is moved from a NEUTRAL position, the open-center passage
of the corresponding implement/travel function is closed in proportion to spool movement.
This reduces the NFC signal to the main pump control valve and the pump output flow is
increased proportionally. When the control valve is fully shifted, the NFC pressure is reduced
to slow return check valve pressure.
The use of an NFC hydraulic system maximizes efficiency of the machine by only producing
flow from the pumps when the flow is needed.
NOTE: A high NFC signal will always overcomes the horsepower control and decrease
pump flow to minimum.


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Text Reference
Main Pumps

Right NFC Control Orifice

Torque Control
Spool

330D / 336D
HYDRAULIC PUMPS
STANDBY

Horsepower
Control Spool

NFC
Spool
Actuator

Main Control Valve
(Right Side)

Drive
Pump

Pilot
Pump

Drive Pump Output
Pressure Sensor

P

M

Power
Shift
PRV

Idler
Pump

Actuator
Pilot System

Destroke

P

Pilot Pump

Main Control Valve
(Left Side)
Idler Pump Output
Pressure Sensor

Left NFC Control Orifice

15

This illustration shows the pumps in STANDBY condition. Each pump control valve group
senses the Negative Flow Control (NFC) signal, the power shift pressure, the cross sensing
pressure, and the system pressure for that pump.
When one of more circuits are activated, the pump control valve groups will upstroke or

destroke the pumps to maintain the pump flow depending on the four signal pressures to the
pump control valve groups.
The pump control valve group controls oil pressure to the left side of the actuator. This
controls the angle of the pump swashplate.
The 330D/336D hydraulic pumps are always trying to upstroke to increase flow. The pump
control valve groups vary the oil pressure used to destroke the hydraulic pumps.