350-375 _sesv1638_01 training
TRANSCRIPT
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Service Training
Meeting Guide 638
TECHNICAL PRESENTATION
350/375 HYDRAULIC EXCAVATORS
PUMPS AND PUMP CONTROLS
SESV1638-01
January 1994
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350/375 HYDRAULIC EXCAVATORSPUMPS AND PUMP CONTROLS
MEETING GUIDE 638 SLIDES AND SCRIPT
AUDIENCE
Level II - Service personnel who understand the principles of machine systems operation, diagnostic
equipment, and procedures for testing and adjusting.
CONTENT
This presentation contains the information and visuals necessary to develop a Level II course of
instruction on the hydraulic pumps and pump controls for the 350 and 375 Hydraulic Excavators.
OBJECTIVES
After learning the information in this presentation, the serviceman will be able to:
1. locate and identify the major components in the hydraulic pumps and pump controls;2. explain the operation of each component in the hydraulic pumps;
3. trace the flow of oil through the pumps and pump controls;
4. locate and identify the test and adjust locations for the margin pressure, constant horsepower
control group, and minimum and maximum angles on the main pumps; and
5. locate and identify the test and adjust locations for the positive flow control, power control, and
minimum and maximum flow rates on the swing pump.
REFERENCES
350 Excavator Hydraulic Systems Operation SENR6116350 Excavator Hydraulic and Electronic Systems Testing and Adjusting SENR6117375 Excavator Hydraulic Systems Operation SENR6024375 Excavator Hydraulic and Electronic Systems Testing and Adjusting SENR6033350 Excavator Parts Book SEBP2250375 Excavator Parts Book SEBP2213
PREREQUISITES
Interactive Video Course "Fundamentals of Mobile Hydraulics" TEVR9001STMG 546 "Graphic Fluid Power Symbols" SESV1546STMG 585 "E/EL300B Excavator--Introduction and System Operation" SESV1585
SUPPLEMENTARY TRAINING MATERIAL
STMG 639 "350/375 Hydraulic Excavators--Hydraulic Systems Operation" SESV1639-01STMG 640 "375 Hydraulic Excavator--Electronic Control Unit" SESV1640STMG 649 "350 Hydraulic Excavator--Electronic Control Unit" SESV1649
Estimated Time: 2 HoursVisuals: 33 (2 X 2) SlidesServiceman Handouts: 5 line drawingsForm: SESV1638-01Date: 1/94
© 1994 Caterpillar Inc.
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TABLE OF CONTENTS
INTRODUCTION ..................................................................................................................5
PUMP CONTROL GROUPS.................................................................................................9
P-Q Curve Description......................................................................................................9Graphic Color Codes.......................................................................................................11
350 PUMP GROUP ..............................................................................................................13
Component Identification ...............................................................................................14
Component Location and Function.................................................................................15
350 PUMP CONTROL GROUP .........................................................................................17
Load Sensing Control .....................................................................................................17
Horsepower Control Group.............................................................................................18
Standby ...........................................................................................................................19
Flow Increase .................................................................................................................21Flow Decrease.................................................................................................................23
375 PUMP GROUP ..............................................................................................................25
Component Location and Function.................................................................................26
Internal Components.......................................................................................................29
Main Pump Regulator.....................................................................................................30
375 PUMP CONTROL GROUP ..........................................................................................31
Standby ...........................................................................................................................31
Flow Increase .................................................................................................................33Flow Decrease.................................................................................................................35
SWING PUMP GROUP.......................................................................................................37
Component Location and Function.................................................................................37
Internal Components.......................................................................................................40
Swing Pump Regulator ...................................................................................................41
SWING PUMP CONTROL OPERATION ..........................................................................42
P-Q CURVE DESCRIPTION...............................................................................................42
Standby ...........................................................................................................................44Flow Increase..................................................................................................................46
Flow Decrease.................................................................................................................49
CONCLUSION.....................................................................................................................51
SLIDE LIST..........................................................................................................................52
SERVICEMAN'S HANDOUTS...........................................................................................53
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INSTRUCTOR NOTES
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INTRODUCTION
The 350 and 375 Hydraulic Excavators are equipped with three
swashplate design, flow on demand hydraulic pumps--two for the main
hydraulic system and one separate pump for the swing system. The two
main hydraulic pumps are load sensing pumps that receive three signal pressures to regulate pump flow. The three signal pressures are:
a. Load sensing pressure from the main control valve
b. Power shift pressure signal from the PRV
c. Hydraulic system pressure
The two main hydraulic pumps on each machine operate similarly but the
pump groups are mechanically and physically different. When all
hydraulic control valves are returned to NEUTRAL, the load sensing
pressure decreases and pump flow is reduced to minimum. When one or more hydraulic control valves are activated, the load sensing pressure
increases and pump flow is regulated in direct proportion to the amount of
pilot control valve (joystick) movement.
• 350 pumps similar to
375 pumps
• Flow on demand
system
• Three signal
pressures regulate
pump flow
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• Swing pump has dual
power setting
• Pump flow controlled
by ECU
• ECU signals PRV
• PRV sends PS signal
to both pumps
• PS signal decrease
destrokes pumps
• PS signal increase
upstrokes pumps
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The swing pump on each machine is identical in operation and physical
appearance. The swing pumps differ from the main hydraulic pumps
because the swing pump is not a load sensing pump, but is a positive
flow pump with dual power settings. In low power, the swing pump
flow output is less. In high power, the swing pump flow output isincreased to provide a more aggressive swing system. The power
settings are controlled automatically. When the power mode selector is
in Power Mode III and the governor speed dial is at 10, the pumps are in
HIGH power. When the power mode selector or the governor speed
dial is in any other position, the swing pump is in LOW power setting.
The two main hydraulic pumps are also controlled by an Electronic
Control Unit (ECU), or controller, as on the 325. Input signals from a
power mode switch (located on the monitor panel in the cab) and an
engine speed pickup (located on the engine flywheel housing) are sentto the controller. The controller processes these input signals and then
sends an electrical signal to a Proportional Reducing Valve (PRV). The
PRV is a solenoid operated pressure reducing valve that sends a
hydraulic signal, called Power Shift (PS) pressure, to both pumps to
help regulate their output. PS pressure works with system pressure to
regulate pump flow. A decrease in PS pressure causes the pumps to
destroke at a lower system pressure, and an increase in PS pressure
causes the pumps to destroke at a higher system pressure.
NOTE TO THE INSTRUCTOR: Only the pumps and pumpcontrols for the 350 and 375 Hydraulic Excavators are discussed in
this presentation. For additional information on the 350 and 375,
refer to STMG 639 "350/375 Hydraulic Excavators--Hydraulic
Systems Operation" (Form SESV1639-01), STMG 649 "350
Hydraulic Excavator--Electronic Control Unit" (Form SESV1649)
and STMG 640 "375 Hydraulic Excavator--Electronic Control
Unit" (Form SESV1640).
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• Hydraulic pump
features
• Independent Pump Controls
• Constant Horsepower Control
• Maximum Angle Stop
• Minimum Angle Stop
• No Negative Flow Control
HYDRAULIC PUMP FEATURES
This slide shows the features of the three hydraulic pumps on the 350 and
375 Hydraulic Excavators. The 350 and 375 main pump groups are
swashplate design, load sensing hydraulic pumps. The pump groups have
the following features:
• Independent pump controls
• Constant horsepower control
• Maximum angle stop
• Minimum angle stop
• No negative flow control
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• Pump differences
• Horsepower Control Follow-up Sleeve inConstant Horsepower Control Group
• Two Springs in the Horsepower Control Group
HYDRAULIC PUMP DIFFERENCES
The 350 main pump groups are different from the 375 main pump groups.
The major differences are:
• Addition of the horsepower control follow-up sleeve in the
constant horsepower control group
• Two springs in the horsepower control group
These differences will be explained later in this presentation.
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• 350 and 375 have
three Power Modes
F L O W
( Q )
PRESSURE (P)
Power Mode III
Power Mode II
Power Mode I
Constant Horsepower Control
Load Sensing Control
MAIN PUMP P-Q CURVE
LS (P-Q)
PUMP CONTROL GROUPS
P-Q Curve Description
The 350 and 375 main pumps operate within three power levels as shown
on this P-Q curve. The operator selects the power level with the Power
Mode switch on the monitor panel. The controller establishes the correct
power mode by electronically modulating a pilot signal which is directed
to the pump controls. In Power Mode III, the system operates withmaximum hydraulic horsepower as shown by the upper P-Q curve. Power
Mode II provides medium hydraulic horsepower as shown by the center
curve. Power Mode I provides low hydraulic horsepower as shown by the
lower portion of the curve.
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• Main pumps contain
load sensing controls
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The main pumps also contain load sensing controls which allow the
pumps to operate at flow rates less than the constant horsepower control
range. The load sensing region on the P-Q curve is illustrated by the
shaded gray area below the constant horsepower control lines. The point
LS (P-Q) illustrates one of the possible pressure and flow ratecombinations during load sensing control.
While pump flow is regulated by the load sensing control, pump flow is
controlled in direct proportion to the amount of implement or travel
function demand. Load sensing control is accomplished through the load
signal signal generated in the main control valve.
The implement load signal generated in the control valves is directed to
the load sensing control valve in the pumps. The load sensing control
valve uses the load signal pressure to regulate pump system pressure to1960 kPa (285 psi) more than the load signal pressure.
The flow rate from the pumps is determined by the control valve
movement as long as system pressure is less than the constant horsepower
regulation pressure.
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• Color codes
Graphic Color Codes
The graphic symbol and sectional view schematics that follow show
different signal pressures, pump system pressures, and conditions. The
color codes for the various pressures are as follows:
Red - Main pump system
pressure (system pressure
between the main pump andthe control valve)
Red and White Stripes - Load sensing signal
pressure
Red Dots - Constant horsepower control
pressure or pressure directed
to the destroke servo piston
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Orange - Pilot pump system pressure
Orange and White Stripes - Reduced pilot pump system
pressure (power shift
pressure from the proportional reducing valve)
Green - Suction, return, and case
drain oil
Yellow - Moving parts and activated
valve envelopes
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• Component locations:
1. Main pumps
2. Swing pump
3. Pilot pump
• Flow from main
pumps regulated by
load sensing control
• Independent pump
operation
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350 PUMP GROUP
The main pump group consists of two main hydraulic system pumps (1),
mounted in tandem, which supply flow to all of the implement and travel
circuits. The pumps are identical in performance. This discussion refers
to the pumps as the front pump (nearest the engine) and the rear pump(farthest from the engine). The front pump is driven by a flexible
flywheel coupling and the rear pump is driven off the rear of the front
pump. The swing pump (2) is mounted at the top and is driven off the
pump drive group. The pilot pump (3) is located on the rear of the swing
pump and is driven off the swing pump drive shaft.
The flow from the main hydraulic pumps is controlled by the load sensing
signal pressure from the hydraulic control valve. The load sensing signal
pressure enters the load sensing control valve on the pump controls. Each
of the pumps has a separate pump control that operates independently.
1
2
3
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• Four adjustment
locations
• Three adjustment
locations shown:
1. Minimum angle
adjustment screw
2. Horsepower control
adjustment screws
3. Load sensing
control adjustment
screw
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Component Identification
This slide shows the main hydraulic pump groups as viewed from the right
rear corner of the machine. Each pump has four adjustment locations to
control flow during different operating conditions:
a. Load sensing control adjustment
b. Constant horsepower control adjustment
c. Minimum angle adjustment
d. Maximum angle adjustment
Three different adjustment locations are shown on the rear pump: The
minimum angle adjustment screw (1) controls the minimum angle of the
swashplate. Turning the screw in (CW) increases the minimum flow and
turning the screw out (CCW) decreases the minimum flow. The maximum
angle adjustment screws are not visible in this slide, but they are located
between the two pump control groups directly in line with the minimumangle adjustment screw.
The constant horsepower control adjustment screw (2) adjusts the point
where the pump starts to destroke. Turning the adjustment screw in (CW)
causes the pump to start destroking at a higher system pressure. The load
sensing control adjustment screw (3) adjusts the margin pressure of the
pumps. Margin pressure is the difference between pump supply pressure
and implement pressure. Turning the screw in (CW) decreases the margin
pressure while turning the screw out (CCW) increases the margin pressure.
1
2
3
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• Pump components
• Two sections of pump
control group
• Load sensing
regulator group
• Constant horsepower
regulator group
HORSEPOWER
DJUSTMENT SCREW
MINIMUM ANGLE
DJUSTMENT SCREW
FRONT
PUMP
CHARGE
PUMP
REAR
PUMP
SWASHPLATE
SERVO PISTON
PUMP CONTROLGROUP
MAXIMUM ANGLE
ADJUSTMENT SCREWS
MINIMUM ANGLE
ADJUSTMENT SCRE
LOAD SENSING
DJUSTMENT SCREW
PUMP AND PUMP CONTROL GROUP
Component Location and Function
This sectional view shows the components of the main hydraulic pump
group. The front and the rear pumps operate identically. The front pump
is driven off the engine flywheel through a flexible coupling. The rear
pump is driven off the front pump.
Each pump control group consists of two separate sections. The load
sensing regulator group uses the load sensing signal pressure from the
hydraulic system to regulate margin pressure. Margin pressure is thedifference in pressure between pump system pressure and the load or
working pressure of the hydraulic system.
The constant horsepower regulator group works with the load sensing
regulator group to control the pump swashplate angle. The horsepower
regulator group uses a load signal pressure, system pressure and power
shift pressure to regulate the pump swashplate angle. Power shift pressure
is generated by a proportional reducing valve as in the 325 excavator.
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• System pressure
upstrokes pumps
• Horsepower control
group directs signal
pressure to minimumangle end of servo
• Servo piston
connected to
swashplate
• Servo piston
connected to
horsepower control
sleeve
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The system pressure is constantly pushing on the maximum angle servo
piston to upstroke the pumps. To regulate the pump flow, the constant
horsepower control group directs a signal pressure (generated from the
system pressure) to and from the minimum angle end of the servo piston.
The servo piston is connected to the swashplate with a pin. The servo piston is also connected to the horsepower control sleeve with a lever and
two pins. The movement of the servo piston moves the swashplate. The
lever then moves the horsepower sleeve in a follow-up arrangement.
The slides that follow show the pumps and pump controls during
operation.
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• Load sensing control
regulates margin
pressure
• Load sensing control
and horsepower
control group regulate
pump flow
CONTROL
VALVE
LOAD SENSING
CONTROL
ADJUSTMENT
LOAD SENSING
PRESSURE SIGNAL
LOAD
SENSING
SPOOL
LOAD
SENSING
SLEEVE
SYSTEM
PRESSURE
PISTON
LOAD SENSING
PRESSURE
PISTON
350 LOAD SENSING CONTROLSTANDBY
350 PUMP CONTROL GROUP
Load Sensing Control
The pump control group consists of two separate control groups. The load
sensing control group regulates the margin pressure while the constant
horsepower control group regulates the point that the pump starts to
destroke.
This sectional view shows the components of the load sensing portion of the pump control group. The load sensing control valve maintains the
margin pressure [2000 kPa (285 psi)] difference between the system
pressure and the implement load pressure. The system pressure enters the
control on the right side. The load sensing pressure signal is generated in
the main control valve and enters the control on the left side. The load
sensing control valve works in conjunction with the constant horsepower
control valve to regulate pump flow.
The load sensing control adjustment screw adjusts the margin pressure.
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• Power shift and
system pressures
regulate pump flow
• Horsepower control
sleeve and servo
piston mechanically
connected
POWER SHIFT
PRESSURE
HYDRAULIC
PUMP AND
CHARGE PUMP
CONTROLVALVE
HORSEPOWER
CONTROL
ADJUSTMENT
HORSEPOWER
CONTROL
SPOOL
HORSEPOWER
CONTROL
SLEEVE
LEVER
POWER SHIFT
PRESSURE
PISTON
TORQUE
CONTROL PISTON
350 HORSEPOWER CONTROL GROUPSTANDBY
Horsepower Control Group
This sectional view shows the components of the horsepower control
portion of the pump controls. The horsepower control group uses the
power shift pressure and system pressure to upstroke or destroke the pump
after a specific system pressure is reached. The horsepower control
adjustment screw adjusts the point that the pump starts to destroke.
The lever in the control is pinned at the top and pivots on the pin. Thelower end of the lever is connected to the servo piston. The horsepower
control sleeve is pinned to the lever. When the servo piston moves, the
sleeve moves in a follow-up arrangement.
In this control, the power shift pressure works against system pressure
during flow regulation. An increase in the power shift pressure means the
system pressure must also increase to destroke the pumps.
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• Pump controls
regulate flow
• Load sensing control
regulates flow during
STANDBY
350 PUMP CONTROLSSTANDBY
POWER SHIFT
PRESSURE
PILOT
PUMP
HYDRAULIC
PUMP AND
CHARGE
PUMP
MINIMUM
ANGLE STOPMAXIMUM
ANGLE STOPSERVO PISTON SWASHPLATE
HORSEPOWER
CONTROL
LOAD SENSING
CONTROL
CONTROL
VALVE
SERVO
PISTON
Standby
This slide shows the components of the pump control group during
STANDBY. The controls work together to regulate the pump flow
according to the demand and hydraulic horsepower requirements. The
pump servo pistons are connected to the swashplate. Pump system
pressure is directed to the maximum angle end of the servo piston at all
times. The load sensing control directs pilot pressure to the minimum
angle servo piston to move the swashplate to the minimum angle for decreased pump flow.
The minimum angle stop screw adjusts the minimum angle of the
swashplate while the maximum angle stop screw adjusts the maximum
angle.
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• Standby pressure
moves load sensing
spool to the left
• Pilot pressure directed
to minimum angle end
of servo piston
• Servo piston movesswashplate to
minimum angle
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When all hydraulic control valves are in NEUTRAL, no signal pressure is
directed to the left side of the load sensing control group. With no signal
pressure on the left end of the load sensing control, standby pressure
moves the load sensing spool to the left.
With the implement and travel controls in NEUTRAL, the electronic
controller sets the power shift pressure to a standby value of
approximately 1725 kPa (250 psi). The controller also energizes the
neutral bypass solenoid valves on the main control valve which allow the
small amount of flow generated by the pumps to return to the tank.
The increased power shift pressure works with the horsepower control
spring to move the horsepower control spool to the right. The left land on
the horsepower control spool blocks the passage to drain. The pilot
pressure is directed around the load sensing spool, through the loadsensing sleeve to the minimum angle servo piston. The servo piston
moves the swashplate to minimum angle.
NOTE: Throughout the discussion of the pump controls operation, it
is assumed that the power shift pressure remains constant. Changes
in power shift pressure can cause an upstroke or destroke of the
pumps.
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• Load sensing spool
drains minimum angle
end of servo piston
• System pressureupstrokes swashplate
• Pump upstrokes
according to flow
demand
PILOT
PUMP
POWER SHIFT
PRESSURE
HYDRAULIC
PUMP AND
CHARGE
PUMP
CONTROL
VALVE
HORSEPOWER
CONTROL
ADJUSTMENT
LOAD SENSING
CONTROL
ADJUSTMENT
LOAD SENSING
SIGNAL PRESSURE
350 PUMP CONTROLSLOAD SENSING PRESSURE INCREASE
START OF UPSTROKE
MINIMUM
ANGLE STOPMAXIMUM
ANGLE STOPSERVO PISTON SWASHPLATESERVO
PISTON
Flow Increase
This slide shows the pump controls at the start of an upstroke condition
that is caused by an increase in the load sensing pressure. When one or
more of the hydraulic control valves are ACTIVATED, a load sensing
pressure signal equal to the implement system pressure is directed to the
left end of the load sensing control group. The signal pressure moves the
load sensing control spool to the right to drain the minimum angle end of
the servo piston.
System pressure on the maximum angle end of the servo piston moves the piston to the right. The servo piston moves the swashplate toward
maximum angle to increase pump flow. The pumps upstroke in direct
relation to the amount of the load sensing pressure signal from the control
valve. The signal pressure is controlled by the amount of the pilot control
valve (joystick) movement.
NOTE TO THE INSTRUCTOR: For more information on the
generation of the load sensing pressure signal, see STMG 639
"350/375 Hydraulic Excavators--Hydraulic Systems Operation"
(Form SESV1639-01).
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• Horsepower control
sleeve meters flow to
and from minimum
angle end of servo
POWER SHIFT
PRESSURE
PILOT
PUMP
HYDRAULIC
PUMP AND
CHARGE
PUMP
CONTROL
VALVE
HORSEPOWER
CONTROL
ADJUSTMENT
LOAD SENSING
CONTROL
ADJUSTMENT
350 PUMP CONTROLSLOAD SENSING PRESSURE INCREASE
END OF UPSTROKE
MINIMUM
ANGLE STOPMAXIMUM
ANGLE STOPSERVO PISTON SWASHPLATESERVO
PISTON
This slide shows the pump controls at the end of UPSTROKE caused by
an increase in the load sensing pressure signal. As the servo piston moves
toward the upstroke position, the lever turns counterclockwise with the
upper pin as the pivot point. The lever moves the horsepower control
sleeve to the right until the horsepower control spool meters flow to and
from the minimum angle end of the servo piston. The horsepower control
spool maintains the pump flow until one or more of the signal pressures
change.
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• Three conditions
cause pumps to
destroke:
a. Load sensing
pressure increase
b. Power shift
pressure decrease
c. System pressure
increase
• System pressure
moves servo to
destroke pump
PILOT
PUMP
POWER SHIFT
PRESSURE
HYDRAULIC
PUMP AND
CHARGE
PUMP
CONTROL
VALVE
HORSEPOWER
CONTROL
ADJUSTMENT
LOAD SENSING
CONTROL
ADJUSTMENT
MINIMUM
ANGLE STOPMAXIMUM
ANGLE STOPSERVO PISTON SWASHPLATESERVO
PISTON
350 PUMP CONTROLSSYSTEM PRESSURE INCREASE
START OF DESTROKE
Flow Decrease
This slide shows the pump controls at the start of DESTROKE caused by
an increase in system pressure.
Three conditions that cause the pumps to destroke are:
a. Load sensing pressure increase
b. Power shift pressure decrease
c. System pressure increase
When system pressure increases, it pushes on the shoulder area of the
torque control piston to move the piston to the left. The power shift
pressure spool and the horsepower control spool also move to the left.
System pressure is directed through the check valve to the right orifice in
the horsepower control sleeve. System pressure goes around the
horsepower control spool, through the center orifice in the horsepower
control sleeve and around the load sensing spool to the minimum angle
end of the servo piston. The increase in system pressure moves the servo
piston and the swashplate toward the destroke position.
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• Servo piston moves
horsepower control
sleeve to left
• Horsepower control
sleeve meters flow to
and from minimum
angle piston
This slide shows the pump controls at the end of DESTROKE caused by
an increase in system pressure. When the servo piston moves to the left,
the lever moves the horsepower control sleeve to the left. The
horsepower sleeve moves to the left until the sleeve reaches a metering
position. The pump flow will remain constant until one of the three signal
pressures going to the pump controls changes.
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• Component locations:
1. Main pump (front)
2. Main pump (rear)
3. Swing pump
4. Pilot pump
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375 PUMP GROUP
The 375 main hydraulic pumps are located behind an access door on the
right rear of the machine. The main pumps, front (1) and rear (2), are
mounted in tandem and driven through a coupling directly off the engine
flywheel. The swing pump (3) is driven by a gear located in the rear gear group of the engine. The pilot pump (4) is mounted in tandem with the
swing pump and is driven by a coupling connected to the swing pump
drive shaft.
1
2
3
4
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• Component locations:
17
STMG 638
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Component Location and Function
This slide shows the main hydraulic pumps on the 375. The major
components visible in this view are:
Regulator groups (1): Contain a load sensing control spool and a
horsepower control spool which are used to control the flow rate of the
pumps. Each main pump has one regulator group which functions
independently.
Pump outlet (2): The front pump (closest to the engine) outlet supplies
oil to the boom and both travel control valves. The rear pump (farthest
from the engine) outlet supplies oil to the stick, bucket and attachment
control valves.
Minimum angle stop adjustment screw (3): The minimum angle stop
adjustment screw for the rear pump is shown. The minimum angle stop
for the front pump is in the same location on the front pump.
Load signal pressure tap (4): The load signal (cylinder or travel
pressure) is supplied by the main control valve and is used by the load
sensing control to establish the correct flow rate depending on demand.
The load sensing control regulates pump flow so that pump output
pressure is held constant at 1960 kPa (285 psi) above the load signal
pressure. This difference between the load signal pressure and the pump
output pressure is called "margin pressure."
1. Regulator groups
2. Pump outlet
3. Minimum angle stop
adjustment screw
4. Load signal
pressure tap
1
2
3
4
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7
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5. Margin pressure
adjustment screw
STMG 638
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Margin pressure adjustment screw (5): The margin pressure
adjustment screw is used to adjust the margin pressure. The margin
pressure adjustment screw is in the same location on the front pump.
Power shift pressure tap (6): The power shift pressure can be measuredat this location.
Pilot pressure tap (7): The pilot pressure can be measured at this tap
(partially visible). Pilot pressure is supplied to the regulator of the main
pumps to destroke the pumps when main system pressure decreases below
pilot system pressure (standby).
Horsepower control adjustment screws: The horsepower adjustment
screws (not visible) for each pump are located on the rear of the regulator
below the power shift pressure test port.
NOTE TO THE INSTRUCTOR: The unpainted valve visible below
the rear pump outlet hose is called the "differential pressure relief
valve." This valve drains the load signal to the tank to destroke the
pump if the difference between the pump output pressure and the
load signal pressure is too high. For more information on the
differential pressure relief valve and the generation of the load
sensing signal, see STMG 639 "350/375 Hydraulic Excavators--
Hydraulic Systems Operation" (Form SESV1639-01). For more
information on the power shift pressure signal and the underspeedcontrol, see STMG 640 "375 Hydraulic Excavator--Electronic
Control Unit" (Form SESV1640) and STMG 649 "350 Hydraulic
Excavator--Electronic Control Unit" (Form SESV1649).
6. Power shiftpressure tap
7. Pilot pressure tap
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• Maximum angle
adjustment screws
(arrows)
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STMG 638
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The maximum angle adjustment screws (arrows) are visible in this slide.
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• Internal components
REGULATOR
MINIMUM ANGLE STOP
DRIVE
SHAFT
SWASHPLATE
MAXIMUM
ANGLE STOP
ROTARY
GROUP
CHARGE
PUMP
DESTROKE
SERVO
UPSTROKE
SERVO
MAIN PUMPINTERNAL COMPONENTS
Internal Components
This slide shows the internal components of the front main pump. The
pump contains a centrifugal charge pump which pressurizes the suction
side of the rotary group to reduce the possibility of cavitation. The pump
generates flow when the pistons in the rotary group (which is connected
by splines to the drive shaft) ride on the inclined surface of the
swashplate. The minimum and maximum angle stops determine the
minimum and maximum pump flows. The regulator controls the amountof pump flow by regulating the oil pressure supplied to the minimum
angle servo and the maximum angle servo.
NOTE: The 375 main hydraulic pumps are similar in operation to
the 994 Wheel Loader steering pump.
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• Two views of main
pump regulator group
shown
MINIMUM
ANGLE SERVO
CONSTANT HORSEPOWER
CONTROL SPOOL
SLOW RETURN CHECK VALVE
MARGIN PRESSURE
ADJUSTMENT
PILOT
PUMP
LOAD SENSING CONTROL SPOOL
LOAD SENSING SIGNAL
MAXIMUM ANGLE SERVO
ACTUATOR PISTON
LEVER
POWER SHIFT
PRESSURE SIGNAL
CONSTANT HORSEPOWER CONTROL SPOOL
MAIN PUMPREGULATORCOMPONENTS
MAINCONTROL
VALVE
SECTION A-A
AA
Main Pump Regulator
This slide shows two sectional views of the main pump regulator. The
upper view shows the regulator looking from the side and the lower view
shows the regulator group from the top.
The upper view shows the maximum angle servo which contains a piston
that acts on a pinned lever. The pinned lever acts on the left end of the
constant horsepower control spool. The constant horsepower controlspool limits the maximum horsepower available from the pump.
In the lower view (Section A-A), the constant horsepower control spool is
shown from a different angle and the load sensing control spool is visible.
A slow return check valve is located between the constant horsepower
control spool and the load sensing control spool. The slow return check
valve allows the pump to destroke freely but restricts the flow of signal oil
to upstroke the pump. The charge pump, main pump and minimum angle
servo are shown as graphic symbols.
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• Pump controls
regulate flow
• Load sensing control
regulates flow during
STANDBY
MAIN PUMPREGULATOR
STANDBY
NEUTRAL BYPASSSOLENOID VALVE
MAIN CONTROL
VALVE
MINIMUM ANGLE
SERVO
CONSTANT HORSEPOWER
CONTROL SPOOL
SLOW RETURN CHECK VALVE
LOAD SENSING
CONTROL SPOOL
MAXIMUM ANGLE SERVO
ACTUATOR PISTON
LEVER
POWER SHIFT
PRESSURE SIGNAL
CONSTANT HORSEPOWER CONTROL SPOOL
SECTION A-A
AA
LOAD SENSINGPRESSURE
SIGNAL LINE
SIDE VIEW
TOP VIEW
375 PUMP CONTROL GROUP
Standby
This slide shows the components of the pump control group during
STANDBY. The controls work together to regulate the pump flow
according to the demand and hydraulic horsepower requirements. The
pump servo pistons are connected to the swashplate. Pump system
pressure is directed to the maximum angle end of the servo piston at alltimes. The load sensing control directs pilot pressure to the minimum
angle servo piston to move the swashplate to the minimum angle for
decreased pump flow.
The minimum angle stop screw adjusts the minimum angle of the
swashplate while the maximum angle stop screw adjusts the maximum
angle.
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• Standby pressure
moves load sensing
spool to the right
STMG 638
1/94
When all hydraulic control valves are in NEUTRAL, no signal pressure is
directed to the right side of the load sensing control group. With no signal
pressure on the right end of the load sensing control, standby pressure
moves the load sensing spool to the right.
With the implement and travel controls in NEUTRAL, the electronic
controller sets the power shift pressure to a standby value of
approximately 1300 kPa (190 psi). The controller also energizes the
neutral bypass solenoid valves on the main control valve which allow the
small amount of flow generated by the pumps to return to the tank.
The increased power shift pressure moves the horsepower control spool to
the left until the center land on the horsepower control spool moves past
the passage to the minimum angle piston. Pilot pressure is directed
around the load sensing spool and around the horsepower control spool tothe minimum angle servo piston. The servo piston moves the swashplate
to minimum angle.
NOTE: Throughout the discussion of the pump controls operation, it
is assumed that the power shift pressure remains constant. Changes
in power shift pressure can cause an upstroke or destroke of the
pumps.
• Pilot pressure directed
to minimum angle end
of servo piston
• Servo piston movesswashplate to
minimum angle
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• Increase in flow due to
increased signal
pressure
MAIN PUMPREGULATOR
UPSTROKE
NEUTRAL BYPASSSOLENOID VALVE
MAIN CONTROL
VALVE
MINIMUM ANGLE
SERVO
CONSTANT HORSEPOWER
CONTROL SPOOL
SLOW RETURN CHECK VALVE
LOAD SENSING
CONTROL SPOOL
MAXIMUM ANGLE SERVO
ACTUATOR PISTON
LEVER
POWER SHIFT
PRESSURE SIGNAL
CONSTANT HORSEPOWER CONTROL SPOOL
SECTION A-A
AA
LOAD SENSINGPRESSURE
SIGNAL LINE
SIDE VIEW
TOP VIEW
Flow Increase
Three conditions that can cause an increase in flow from main pumps are:
1. An increase in the load sensing signal
2. An increase in power shift pressure
3. A decrease in pump output pressure
This slide shows a pump flow increase due to an increase in the load
sensing signal pressure. When the load signal increases, the load signal
pressure plus the spring force on the right end of the load sensing spool
exceed the force of the pump output pressure on the left end of spool. The
combined forces on the right end of the spool move the load sensing spool
to the left, connecting the passage from the slow return check valve to the
tank.
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• Balanced pumps
STMG 638
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When the pump is in balance, the horsepower control spool is positioned
so that the passage to the slow return check valve is slightly open to the
passage to the minimum angle servo. Since these passages are connected,
shifting the load sensing control spool to the left allows the oil in the
minimum angle servo to return to the tank through the slow return check valve and load sensing control spool.
With the minimum angle servo open to the tank, pump output pressure (or
pilot pressure, whichever is higher) acting on the maximum angle servo
rotates the swashplate counterclockwise to upstroke the pump. When the
maximum angle servo shifts to the left, the mechanical advantage of the
actuator piston against the lever increases and the lever rotates clockwise.
When the lever rotates clockwise, the horsepower control spool shifts
back to the right, which restricts the oil in the minimum angle servo from
returning to the tank and stops the swashplate from moving.
When implement or travel circuit approaches full operation and the
difference between the load signal pressure and the pump output pressure
decreases below the margin pressure setting, the load sensing spool then
becomes “disabled” (remains fully shifted to the left). When the load
sensing spool is disabled, the horsepower control spool regulates pump
flow by alternately pressurizing the oil in the minimum angle servo or
returning the oil to the tank. With the load sensing regulator disabled,
either an increase in power shift pressure or a decrease in pump output
pressure will upstroke the pump.
• Full operation of
implement or travel
• Load sensing spool
disabled when system
pressure is lower than
margin pressure
• Minimum angle servo
open to tank
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MAIN PUMPREGULATOR
DESTROKE
NEUTRAL BYPASSSOLENOID VALVE
MAIN CONTROL
VALVE
MINIMUM ANGLE
SERVO
CONSTANT HORSEPOWER
CONTROL SPOOL
SLOW RETURN CHECK VALVE
LOAD SENSING
CONTROL SPOOL
MAXIMUM ANGLE SERVO
ACTUATOR PISTON
LEVER
POWER SHIFT
PRESSURE SIGNAL
CONSTANT HORSEPOWER CONTROL SPOOL
SECTION A-A
AA
LOAD SENSINGPRESSURE
SIGNAL LINE
SIDE VIEW
TOP VIEW
Flow Decrease
Three conditions that can cause a decrease in the main pump flow are:
1. An increase in the system pressure
2. A decrease in the load sensing control pressure
3. A decrease in the power shift control signal pressure
This slide shows a decrease in flow due to an increase in system pressure.
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• Lever rotates
clockwise
• Horsepower control
spool moves to the
right• System pressure
directed to minimum
angle servo
• Mechanical advantage
changes as actuator
piston moves toward
lever pivot point
STMG 638
1/94
When system pressure increases, the upward force on the shoulder area of
the actuator piston increases and the piston rotates the lever clockwise.
The lever forces the horsepower control spool to the right against the
force of the horsepower control spring and the power shift pressure.
Shifting the horsepower control spool to the right connects the minimumangle servo to system pressure in the internal passage to the left of the
horsepower control spool. Since the area of the minimum angle servo is
larger than the maximum angle servo, the swashplate rotates clockwise to
destroke the pump. When the swashplate rotates clockwise, the
maximum angle servo moves to the right. Moving the servo to the right
decreases the mechanical advantage of the actuator piston on the lever.
The reduction in mechanical advantage allows the horsepower control
spool to shift back to the left, blocking the maximum angle servo
connection to system pressure. At this point, the swashplate stops
rotating and balances.
If the power shift signal pressure decreases, moving the horsepower
control spool to the right becomes easier and the pump begins to destroke
at a lower system pressure. If the power shift signal pressure increases,
moving the horsepower control spool to the right becomes more difficult
and the pump begins to destroke at a higher system pressure.
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• 350 swing pump
components:
1. Regulator group
24
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SWING PUMP GROUP
Component Location and Function
This slide shows the swing pump on the 350. The major components
visible in this view are:
Regulator group (1): The regulator group contains the positive flow
control and horsepower control spools.
Swing power control signal line (2): The swing power control solenoid
valve provides a pilot pressure signal during swing operation in Power
Mode III for maximum swing horsepower. In Power Modes II and I, the
swing power control solenoid allows oil in this signal line to return to the
tank.
Horsepower control adjustment (3): The horsepower control regulates
swing pump flow according to swing output pressure. The adjustment
screw is located behind the fitting where the swing power control pilot
signal hose is connected to the regulator group.
3. Horsepower control
adjustment
2. Swing power
control signal line
1 2
3
4
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4. Positive flow
control signal line
STMG 638
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Positive flow control signal line (4): Swing pilot control pressure is
directed to the swing pump through this line (near the drive end of the
pump). The positive flow control function reduces swing pump flow to
minimum when the swing circuit is not operating. During fine swing
operation, the positive flow control system increases fine swingcontrollability by increasing the swing pump flow in direct proportion to
swing pilot lever movement. The positive flow control adjustment screw
is on the rear of the regulator group and is not visible in this slide.
Pump outlet (5): Swing pump flow is directed through this line to the
swing control valve on the rear swing motor.
Maximum angle adjustment (6): The maximum angle adjustment
screw is located on top of the swing pump and is not visible in this slide.
The maximum flow rate from the swing pump can be adjusted with thisscrew. The minimum flow rate adjustment screw is on the bottom of the
pump and is also not visible in this slide.
6. Maximum angle
adjustment
5. Pump outlet
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• 375 Swing pump
components:
1. Regulator group
2. Swing power
control signal line
3. Horsepower controladjustment
4. Positive flow
control signal line
5. Pump outlet
6. Maximum angle
adjustment
25
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This slide shows the swing pump on the 375. The major components
have the same functions as previously described for the 350.
12
3
4
5
6
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• Swing pumps on 350
and 375 are similiar
• Swing pump different
from main pumps
DRIVE
SHAFT
MINIMUM ANGLE STOP
MAXIMUM ANGLE SERVO
SWASHPLATE
MAXIMUM ANGLE STOP ROTARY GROUP MINIMUM ANGLE SERVO
CHARGE PUMP
COUPLING
REGULATOR
SWING PUMPINTERNAL COMPONENTS
Internal Components
The internal components of the swing pumps used on the 350 and 375 are
very similar. The swing pump has a coupling on the rear end of the drive
shaft that is used to drive the pilot pump. The swing pump and the swing
pump regulator are completely different from the main hydraulic pumps
and the pump regulator groups.
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• Positive flow control
and horsepower
control spools shown
• Pilot pressure directed
to both servo pistons
• Swashplate moves to
minimum angle
SWING PUMPREGULATORCOMPONENTS
SECTION A-A
LEVER
ACTUATOR PISTON
MINIMUN ANGLE SERVO
POSITIVE FLOW CONTROL
PILOT PORT
SWING POWER CONTROL
PILOT PORT
MAXIMUM ANGLE
SERVO
POSITIVE FLOW CONTROL
SPOOL
HORSEPOWER CONTROL SPOOL
HORSEPOWER CONTROL SPOOL
POSITIVE FLOW CONTROL SPOOL
A
A
SWING CONTROLVALVE
SIDE VIEW
TOP VIEW
Swing Pump Regulator
This slide shows the components of the swing pump regulator group. The
upper view shows the regulator from the side. The lower view (Section
A-A) shows the regulator from the top. The positive flow control and
horsepower control spools are visible in both views.
In STANDBY, pilot system pressure is directed to the maximum angle and
minimum angle servo pistons. Since the minimum angle servo piston islarger than the maximum angle servo, the mechanical advantage pushes
the swashplate to minimum angle.
NOTE: The adjustment screw above the swing horsepower control
adjustment is turned completely in and is not functional on the swing
pump regulator group.
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• Graph on left shows
positive flow control
characteristics
• Graph on right shows
horsepower control
flow characteristics
• Swing pump
upstrokes in
proportion to swing
pilot pressure
F L O W
( Q )
SYSTEM PRESSURE (P)
POWER MODE III
CONSTANT HP CONTROL
F L O W
( Q )
PFC SIGNAL PRESSURE (P)
POSITVE FLOW CONTROL
SWING PUMP P-Q CURVES
POWER MODESI AND II
SWING PUMP CONTROL OPERATION
P-Q Curve Description
This slide shows the P-Q curves for the swing pump. The graph on the
left shows the flow characteristics of the positive flow control function
and the graph on the right shows the flow characteristics of the
horsepower control.
The vertical axis on the positive flow control curve is swing pump flow.
The horizontal axis is the positive flow control pilot signal pressure
(swing pilot pressure). The curve shows when the swing pilot controls are
in NEUTRAL and the swing pilot pressure is at STANDBY pressure
[approximately 400 kPa (60 psi)], the swing pump flow is reduced to
minimum. When the swing pilot control pressure increases to
approximately 900 kPa (130 psi), the swing pump starts to upstroke. As
the swing pilot pressure increases to more than 900 kPa (130 psi), the
swing pump upstrokes proportionally until the swing pilot pressure
increases to approximately 1760 kPa (255 psi). At this pressure, the
swing pump flow is maximum.
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• Two power levels for
swing pump
STMG 638
1/94
The vertical axis on the constant horsepower control curve is the swing
pump flow. The horizontal axis is the swing pump system pressure. The
curve shows two separate power levels for the swing pump. The upper
power level curve is obtained in Power Mode III, while the lower power
level curve is for Power Modes I and II.
The following slides illustrate how the swing pump regulator controls the
swing pump flow.
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• STANDBY condition
• Pilot pressure more
than swing system
pressure
• In STANDBY pilot
pressure controls
swing pump flow
SWING PUMPREGULATOR
STANDBY
SECTION A-A
LEVER
ACTUATOR PISTON
MINIMUN ANGLE SERVO
POSITIVE FLOW CONTROL
PILOT PORT
SWING POWER CONTROL
PILOT PORT
MAXIMUM ANGLE
SERVO
POSITIVE FLOW CONTROL
SPOOL
HORSEPOWER CONTROL SPOOL
HORSEPOWER CONTROL SPOOL
POSITIVE FLOW CONTROL SPOOL
A
A
SWING CONTROLVALVE
SIDE VIEW
TOP VIEW
Standby
This slide shows the swing pump regulator in the STANDBY position
when the swing pilot control valve (joystick) is in NEUTRAL.
In STANDBY, the pilot system pressure is more than the swing system
pressure. Pilot pressure is directed through the resolver to the end of the
maximum angle servo piston. The pilot pressure flows through the center
of the maximum angle piston to the center section of the actuator piston.The pilot pressure pushes up on the shoulder area of the actuator piston,
but the force is not enough to compress the spring on the horsepower
control spool. The spring force holds the horsepower control spool to the
left.
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• Positive flow control
signal line open to
tank
• Pilot pressure holds
swashplate at
minimum angle
STMG 638
1/94
When the swing pilot controls are in NEUTRAL, the positive flow control
signal line is open to the tank. The force of the spring on the right end of
the positive flow control spool shifts the spool to the left. With the spool
shifted to the left, the pilot pressure flows through the internal passages,
around the positive flow control spool and around the horsepower controlspool to the minimum angle servo piston. The minimum angle piston is
larger than the maximum angle piston. The mechanical advantage of the
minimum angle piston moves the swashplate to the minimum angle to
reduce pump flow.
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• Conditions that
increase pump flow:
1. Positive flow
control pressure
increase
2. Swing system
pressure decrease
3. Swing power control pressure
increase
• Increase in pilot
activation pressure
upstrokes pump
SWING PUMP REGULATORUPSTROKE
HIGH POWER MODE
SECTION A-A
LEVER
ACTUATORPISTON
MINIMUN ANGLE SERVO
POSITIVE FLOW CONTROL
PILOT PORT
MAXIMUM ANGLE
SERVO
POSITIVE FLOW CONTROL
SPOOL
HORSEPOWER CONTROL SPOOL
HORSEPOWER CONTROL SPOOL
POSITIVE FLOW CONTROL SPOOL
A
A
SIDE VIEW
TOP VIEW
SWING CONTROLVALVE
PILOT PRESSUREFROM SWING
CONTROL VALVE
PILOT PRESSUREFROM SWING
POWER CONTROLSOLENOID
SWING POWER CONTROLPILOT PORT
PILOT PRESSUREFROM SWING
POWER CONTROLSOLENOID
Flow Increase
Three conditions which cause an increase in flow are:
1. An increase in the positive flow control pilot pressure
2. A decrease in the swing system pressure
3. An increase in the swing power control pressure
This slide shows an increase in pump flow caused by an increase in the
positive flow control pilot pressure when the swing power control is in the
LOW power mode. When the swing pilot control valve is activated, the
pilot pressure is directed to shift the swing control valve. The same pilot
signal pressure is directed to the positive flow control signal port in the
swing pump regulator group. The increase in the pilot pressure pushes the
positive flow control spool to the right. When the positive flow control
spool moves to the right, the minimum angle servo piston is opened to
case drain through the horsepower control spool and the positive flow
control spool. The system pressure oil pushes the maximum angle servo
to the left to upstroke the pump.
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• Swing pilot pressure
determines amount of
positive flow control
spool movement
• Positive flow control
spool fully shifted at
255 psi pilot pressure
• Pump flow regulatedby constant
horsepower control
• Actuator piston movesalong lower side of
lever changing
mechanical advantage
• Swashplate reaches
balance point
STMG 638
1/94
When the servo moves to the left, the actuator piston housing increases
the spring force on the right end of the positive flow control spool. The
positive flow control spool shifts to the left closing the passage from the
minimum angle servo to the tank. The swashplate stops rotating. The
amount of positive flow control spool movement to the right is in direct proportion to the amount of swing system pilot activation pressure on the
left end of the spool.
When the swing pilot pressure exceeds approximately 3100 kPa (255 psi),
the positive flow control spool is fully shifted to the right allowing the oil
in the minimum angle servo piston to drain (depending on the horsepower
control spool position). In this condition, the pump is free to upstroke to
maximum flow.
When the positive flow control spool is fully shifted to the right, the pumpflow is regulated by the horsepower control spool. If the system pressure
decreases, the force from the actuator piston pushing up on the lever
decreases. The spring force pushes the horsepower control spool to the
left, rotating the lever counterclockwise. When the horsepower control
spool shifts to the left, the oil from the minimum angle servo drains
through the positive flow control spool. The system pressure acting on
the maximum angle servo then forces the servo to the left to upstroke the
pump.
When the servo moves to the left, the actuator piston moves along thelower side of the lever. This movement changes the mechanical
advantage of the actuator piston acting on the lever. The lever then
rotates clockwise pushing the horsepower control spool back to the right.
The center land on the horsepower control spool meters flow to and from
the minimum angle servo piston. The swashplate is balanced at this
position until one or more of the separate control pressures changes.
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• HIGH power mode
• Increase in power
control pressure
increases system
pressure
• Swing power control
pilot pressure equal to
positive flow pilot
pressure
SWING PUMPREGULATOR
UPSTROKELOW POWER MODE
SECTION A-A
LEVER
ACTUATORPISTON
MINIMUN ANGLE SERVO
POSITIVE FLOW CONTROL
PILOT PORT
SWING POWER CONTROL
PILOT PORT
MAXIMUM ANGLE
SERVO
POSITIVE FLOW CONTROL
SPOOL
HORSEPOWER CONTROL SPOOL
HORSEPOWER CONTROL SPOOL
POSITIVE FLOW CONTROL SPOOL
A
ASIDE VIEW
TOP VIEW
SWING CONTROLVALVE
PILOT PRESSUREFROM SWING
CONTROL VALVE
This slide shows the swing pump regulator in the HIGH power mode
during upstroke. While the swing pump flow is being regulated by the
horsepower control, an increase in the swing power control signal
pressure will increase the spring force on the horsepower control spool,
push the horsepower control spool to the left, and upstroke the pump as
previously described.
The pilot pressure from the swing power control solenoid is equal to the
pilot pressure going to the positive flow control pilot port. When swing pilot activation pressure increases to approximately 3100 kPa (255 psi),
the positive flow control spool is fully shifted to the right and the swing
power control mechanism is fully shifted to the left. The swing system
pressure must then increase before the pump starts to destroke.
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• Conditions that
decrease pump flow:
1. Increase in system
pressure
2. Decrease in swing
power control
pressure
3. Decrease in positiveflow control signal
pressure
• Positive flow control
spool shifted to right
SWING PUMPREGULATOR
DESTROKE
SECTION A-A
LEVER
ACTUATORPISTON
MINIMUN ANGLE SERVO
POSITIVE FLOW CONTROL
PILOT PORTSWING POWER CONTROL
PILOT PORT
MAXIMUM ANGLE
SERVO
POSITIVE FLOW CONTROL
SPOOL
HORSEPOWER CONTROL SPOOL
HORSEPOWER CONTROL SPOOL
POSITIVE FLOW CONTROL SPOOL
A
ASIDE VIEW
TOP VIEW
SWING CONTROLVALVE
Flow Decrease
Three conditions which cause a decrease in swing pump flow are:
1. An increase in the system pressure
2. A decrease in the swing power control pressure
3. A decrease in the positive flow control signal pressure
This slide shows a decrease in flow due to an increase in the swing system
pressure. The pilot control pressure is more than 1760 kPa (255 psi) and
the positive flow control spool is fully shifted to the right.
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• Actuator piston
rotates lever
clockwise
• Horsepower control
spool directs systempressure to minimum
angle piston
• Mechanical advantage
changes as actuator
piston moves along
lever
• Swashplate reaches a
balance point
• Less power control
signal destrokes
pump sooner
• Pump flow decreases
as swing pilot
pressure decreases
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As the swing system pressure increases, the upward force on the actuator
piston increases and rotates the lever clockwise. The horsepower control
spool moves to the right against the force of the horsepower control
spring and the swing power control signal pressure. The horsepower
control spool connects the minimum angle servo to the system pressure.Since the area of the minimum angle servo is larger than the area of the
maximum angle servo, the swashplate rotates clockwise to destroke the
pump. When the swashplate rotates clockwise, the maximum angle servo
moves to the right. Moving the servo to the right decreases the
mechanical advantage of the actuator piston on the lever. The reduction
in the mechanical advantage allows the horsepower control spool to shift
back to the left, blocking the maximum angle servo connection to the
system pressure. At this point, the swashplate stops rotating and balances.
If the swing power control signal pressure decreases, moving thehorsepower control spool to the right becomes easier and the pump begins
to destroke at a lower pressure.
During positive flow control, pump flow will decrease when the positive
flow control signal pressure (swing pilot pressure) decreases. Destroking
the pump by positive flow control occurs when the positive flow control
spool shifts to the left due to a decrease in swing pilot pressure. When
shifted to the left, the spool connects the left internal passage above the
spool to the system pressure in the right internal passage. System
pressure pushes on the minimum angle servo and horsepower controlspool as previously described.
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CONCLUSION
This presentation has discussed the operation of the pumps and pump
controls for the 350 and 375 Hydraulic Excavators. When used in
conjunction with the Service Manual, the information in this package
should permit the serviceman to do a thorough job of analyzing problemsin these pumps and pump controls.
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SLIDE LIST
1. Model View
2. Pump Similarities to 375
3. Pump Differences from 3754. Pump P-Q Curve
5. Graphic Color Codes
6. 350 Pump Group
7. 350 Pump Group Close View
8. 350 Pump Group Sectional View
9. 350 Load Sensing Control Sectional
View
10. 350 Horsepower Control Sectional
View
11. 350 Pump Controls (Standby)12. 350 Pump Controls (Start of Upstroke)
13. 350 Pump Controls (End of Upstroke)
14. 350 Pump Controls (Start of Destroke)
15. 350 Pump Controls (End of Destroke)
16. 375 Pump Group
17. 375 Pump Components
18. 375 Pump Max. Angle Screws
19. 375 Pump Internal Components
20. 375 Pump Regulator 21. 375 Pump Controls (Standby)
22. 375 Pump Controls (Upstroke)
23. 375 Pump Controls (Destroke)
24. 350 Swing Pump View
25. 375 Swing Pump View
26. Swing Pump Sectional View
27. Swing Pump Regulator Components
28. Swing Pump P-Q Curves
29. Swing Pump Controls (Standby)
30. Swing Pump Controls (Upstroke) LowPower
31. Swing Pump Controls (Upstroke)
High Power
32. Swing Pump Controls (Destroke)
33. Model View
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H O R S E P O W E R
A D J U S T M E N T
S C R E W
M I N I M U M A N G L E
A D J U S T M E N T
S C R E W
F R O N T
P U M P
C H A R G E
P U M P
R E A R
P U M P
S W A S H P L A T E
S E R V O P I S
T O N
P U M P
C O N T R O L
G R O U P
M
A X I M U M A N G L E
A D J U S T M E N T
S C R E W S
M I N I M
U M A N G L E
A D J
U S T M E N T
S
C R E W
3 5 0
P U M P A N D P
U M P C O N T R O
L G R O U P
L O A D S E N S I N G
A D J U S T M E N T
S C R E W
Serviceman's Handout No. 1
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3 5 0 P U M
P C O N T R O L S
S T A N D B Y
P O W E R S H I F
T
P R E S S U R E
P I L O T
P U M P
H Y D R A U L I C
P U M P
A N D
C H A R G E
P U M P
M I N I M U M
A N G L E
S T O P
M A X I M U M
A N G L E
S T O P
S E R V O
P I S T O N
S W A S H P L A T E
H O R S E P O W E R
C O N T R O L
L O A D S E N S I N G
C O N T R O
L
C O N T R O L
V A L V E
Serviceman's Handout No. 2
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M A I N P U M P R E G U L A T O R
S T A N D B Y
N E U T R A L B Y P A S S
S O L E N O I D V A L V E
M A I N H Y D R A U L I C
C O N T R O L
V A L V E
M I N I M U M A N G L E
S E R V O
C O N S T A N T H O R S E P O W E R
C O N T R O L S P O O L
S L O W R
E T U R N C H E C K V A L V E
L
O A D S E N S I N G C O N T R O L S P O O L
M
A X I M U M A N G L E S E R V O
A
C T U A T O R P I S T O N
L
E V E R
P O W E R S H I F T
P R E S S U R E S I G N A L
C O N S T A N T H O R S E P O W E R C O N T R O L
S P O O L
S E C T I O N
A - A
A
A
L O A D S E N S I N G
P R E S S U R E
S I G N A L L I N E
S I D E
V I E W
T O P V I E W
Serviceman's Handout No. 4
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S W I N G
P U M P R E G U L A T O R
S T A N D B Y
S E C T I O N A - A
L E V E R
A C T U A T O R P I S T O N
M I N I M U N A N G L E S E R V O
P O S I T I V E F L O W C
O N T R O
L
P I L O T P O R T
S W I N G P O W E R
C O N T R O L
P I L O T P O R T
M A X I M U M
A N G L E S E R V O
P O S I T I V E
F L O W C
O N T R O L
S P O O L
H O
R S E P O W E R C O N T R O L S P O O L
H O R S E P O W E R C O N T R O L S P
O O L
P O S I T I V E F L O W C
O N T R O L S P O O L
A
A
S W I N G C O N T R O L
V A L V E
S I D E V I E W
T O P V I E
W
Serviceman's Handout No. 5
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INSTRUCTOR NOTES
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INSTRUCTOR NOTES
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