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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


Internal Components.......................................................................................................29

Main Pump Regulator.....................................................................................................30

375 PUMP CONTROL GROUP ..........................................................................................31

Standby ...........................................................................................................................31

Flow Increase .................................................................................................................33Flow Decrease.................................................................................................................35

SWING PUMP GROUP.......................................................................................................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


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


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


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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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


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


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


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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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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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

56

7

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5. Margin pressure

adjustment screw

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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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- 28 -

• Maximum angle

adjustment screws

(arrows)

18

STMG 638

1/94

The maximum angle adjustment screws (arrows) are visible in this slide.

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19

- 29 -STMG 638

1/94

• 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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20

- 30 -STMG 638

1/94

• 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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21

- 31 -STMG 638

1/94

• Pump controls

regulate flow


regulates flow during

STANDBY

MAIN PUMPREGULATOR

STANDBY

NEUTRAL BYPASSSOLENOID VALVE

MAIN CONTROL

VALVE

MINIMUM ANGLE

SERVO

CONSTANT HORSEPOWER

CONTROL SPOOL


LOAD SENSING

CONTROL SPOOL

MAXIMUM ANGLE SERVO

ACTUATOR PISTON

LEVER

POWER SHIFT

PRESSURE SIGNAL


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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- 32 -

• 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.


to minimum angle end

of servo piston

• Servo piston movesswashplate to

minimum angle

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22

- 33 -STMG 638

1/94

• Increase in flow due to

increased signal

pressure

MAIN PUMPREGULATOR

UPSTROKE


MAIN CONTROL

VALVE

MINIMUM ANGLE

SERVO

CONSTANT HORSEPOWER

CONTROL SPOOL


LOAD SENSING

CONTROL SPOOL

MAXIMUM ANGLE SERVO

ACTUATOR PISTON

LEVER

POWER SHIFT

PRESSURE SIGNAL


SECTION A-A

AA


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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- 34 -

• Balanced pumps

STMG 638

1/94

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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23

- 35 -STMG 638

1/94

MAIN PUMPREGULATOR

DESTROKE


MAIN CONTROL

VALVE

MINIMUM ANGLE

SERVO

CONSTANT HORSEPOWER

CONTROL SPOOL


LOAD SENSING

CONTROL SPOOL

MAXIMUM ANGLE SERVO

ACTUATOR PISTON

LEVER

POWER SHIFT

PRESSURE SIGNAL


SECTION A-A

AA


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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- 36 -

• Lever rotates

clockwise


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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- 37 -

• 350 swing pump

components:

1. Regulator group

24

STMG 638

1/94

SWING PUMP GROUP


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

56

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- 38 -

4. Positive flow

control signal line

STMG 638

1/94

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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- 39 -

• 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

STMG 638

1/94

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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26

- 40 -STMG 638

1/94

• 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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27

- 41 -STMG 638

1/94

• Positive flow control

and horsepower

control spools shown


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


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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28

- 42 -STMG 638

1/94

• 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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- 43 -

• 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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29

- 44 -STMG 638

1/94

• 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


PILOT PORT

SWING POWER CONTROL

PILOT PORT

MAXIMUM ANGLE

SERVO


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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- 45 -


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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30

- 46 -STMG 638

1/94

• 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


PILOT PORT

MAXIMUM ANGLE

SERVO


SPOOL




A

A

SIDE VIEW

TOP VIEW

SWING CONTROLVALVE

PILOT PRESSUREFROM SWING

CONTROL VALVE


POWER CONTROLSOLENOID

SWING POWER CONTROLPILOT PORT


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.

8/9/2019 350-375 _SESV1638_01 training


- 47 -

• Swing pilot pressure

determines amount of

positive flow control

spool movement


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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31

- 48 -STMG 638

1/94

• 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


PILOT PORT

SWING POWER CONTROL

PILOT PORT

MAXIMUM ANGLE

SERVO


SPOOL




A

ASIDE VIEW

TOP VIEW

SWING CONTROLVALVE


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.

8/9/2019 350-375 _SESV1638_01 training


32

- 49 -STMG 638

1/94

• Conditions that

decrease pump flow:

1. Increase in system

pressure

2. Decrease in swing

power control

pressure

3. Decrease in positiveflow control signal

pressure


spool shifted to right

SWING PUMPREGULATOR

DESTROKE

SECTION A-A

LEVER

ACTUATORPISTON

MINIMUN ANGLE SERVO


PILOT PORTSWING POWER CONTROL

PILOT PORT

MAXIMUM ANGLE

SERVO


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.

8/9/2019 350-375 _SESV1638_01 training


- 50 -

• Actuator piston

rotates lever

clockwise


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

STMG 638

1/94

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.

8/9/2019 350-375 _SESV1638_01 training


- 51 -

33

STMG 638

1/94

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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- 52 -STMG 638

1/94

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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1/94

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


C O N T R O

L

C O N T R O L

V A L V E


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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


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


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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


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INSTRUCTOR NOTES

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INSTRUCTOR NOTES

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350-375 _SESV1638_01 training