Woodward UG40 Guide

B03575.C
UG40 GOVERNOR WITH DIGITAL INTERFACE (UG40-DI)
Software versions 3.07/3.08/4.01/4.02
INSTALLATION AND COMMISSIONING MANUAL

!
WARNING
Read this entire manual and all other publications pertaining to the work to be
performed before installing, operating, or servicing this equipment. Practice all plant
and safety instructions and precautions. Failure to follow instructions can cause
personal injury and/or property damage.
!
WARNING
The engine, turbine, or other type of prime mover should be equipped with an
overspeed (overtemperature, or overpressure, where applicable) shutdown device(s),
that operates totally independently of the prime mover control device(s) to protect
against runaway or damage to the engine, turbine, or other type of prime mover with
possible personal injury or loss of life should the mechanical-hydraulic governor(s) or
electric control(s), the actuator(s), fuel control(s), the driving mechanism(s), the
linkage(s), or the controlled device(s) fail.
!
CAUTION
To prevent damage to a control system that uses an alternator or battery-charging device,
make sure the charging device is turned off before disconnecting the battery from the system.
!
CAUTION
Electronic controls contain static-sensitive parts. Observe the following precautions to prevent
damage to these parts.
• Discharge body static before handling the control (with power to the control turned off,
contact a grounded surface and maintain contact while handling the control).
• Avoid all plastic, vinyl, and Styrofoam (except antistatic versions) around printed circuit
boards.
• Do not touch the components or conductors on a printed circuit board with your hands
or with conductive devices.
• When not installed in a control, modules should be kept in a protective antistatic bag.
☞Revisions in this manual are marked by a vertical line in the margin.
Woodward reserves the right to update any portion of this publication at any time.
Information provided by Woodward is believed to be correct and reliable. However,
no responsibility is assumed by Woodward unless otherwise expressly
undertaken.
© Woodward, 2001
All Rights Reserved

Manual B03575.C UG40-DI Manual
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Table of Contents
1. GENERAL INFORMATION......................................................................................................1
1.1 INTRODUCTION............................................................................................................................1
1.2 DESCRIPTION..............................................................................................................................1
1.3 SYSTEM COMPLIANCE .................................................................................................................1
1.4 GENERAL SAFETY PRECAUTIONS .................................................................................................1
1.5 NOTES, WARNINGS AND CAUTIONS..............................................................................................1
1.6 IDENTIFICATION PLATE.................................................................................................................2
1.7 TECHNICAL DATA ........................................................................................................................2
1.8 SOFTWARE VERSIONS .................................................................................................................2
2. ESD PROTECTION AND HANDLING.....................................................................................6
3. DESCRIPTION..........................................................................................................................7
3.1 INTRODUCTION............................................................................................................................7
3.2 DI CONTROL PANEL AND GOVERNOR DIAL PLATE.........................................................................7
3.3 MECHANICAL GOVERNOR.............................................................................................................7
3.3.1 Introduction...................................................................................................................7
3.3.2 Component description ................................................................................................7
3.3.3 Operation of the UG40-DI Mechanical Part .............................................................. 12
3.4 DIGITAL INTERFACE .................................................................................................................. 14
3.4.1 Introduction................................................................................................................ 14
3.4.2 Component Description............................................................................................. 15
3.4.3 Operation................................................................................................................... 15
4. INSTALLATION..................................................................................................................... 16
4.1 INTRODUCTION......................................................................................................................... 16
4.2 INSTALLATION REQUIREMENTS.................................................................................................. 16
4.3 UNPACKING.............................................................................................................................. 16
4.4 STORAGE................................................................................................................................. 16
4.5 MOUNTING THE GOVERNOR ...................................................................................................... 16
4.6 LINKAGE ATTACHMENTS ........................................................................................................... 17
4.7 OIL SUPPLY ............................................................................................................................. 18
4.8 ELECTRICAL CONNECTIONS ...................................................................................................... 21
5. GOVERNOR MECHANICAL OPERATION AND ADJUSTMENTS ..................................... 22
5.1 INTRODUCTION......................................................................................................................... 22
5.2 CHECK THE MAXIMUM SPEED SETTING...................................................................................... 22
5.3 INITIAL OPERATION FOR A NEW GOVERNOR – MECHANICAL ....................................................... 22
5.3.1 Adjustments............................................................................................................... 22
5.3.2 Compensation Adjustments ...................................................................................... 22
5.4 READING SETTINGS FROM MECHANICAL GOVERNOR ON THE ENGINE.......................................... 24
5.4.1 Procedure.................................................................................................................. 24
6. CALIBRATION OF THE DIGITAL INTERFACE................................................................... 25
6.1 INTRODUCTION......................................................................................................................... 25
6.1.1 Calibration on test bench........................................................................................... 25
6.1.2 Calibration on engine ................................................................................................ 25
6.2 FUNCTIONS OF UG40-DI DURING CALIBRATION......................................................................... 25
6.2.1 Introduction................................................................................................................ 25
6.2.2 Explanation of the UG40-DI panel during calibration................................................ 25
6.3 CALIBRATION ON TEST BENCH .................................................................................................. 27
6.3.1 Procedure.................................................................................................................. 27
6.4 CALIBRATION ON ENGINE.......................................................................................................... 28
6.4.1 Procedure.................................................................................................................. 28
6.5 CALIBRATION FLOW CHART....................................................................................................... 28

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7. ADJUSTMENT OF THE DIGITAL INTERFACE ...................................................................31
7.1 INTRODUCTION .........................................................................................................................31
7.1.1 Adjustment.................................................................................................................31
7.1.2 Fine tuning.................................................................................................................31
7.2 FUNCTIONS OF UG40-DI DURING ADJUSTMENT......................................................................... 31
7.2.1 Introduction................................................................................................................31
7.2.2 Explanation of the UG40-DI panel during calibration and adjustment ......................31
7.2.3 Displaying values on the Dial Panel speed setting knob and speed indicator..........34
7.3 ADJUSTMENT............................................................................................................................34
7.3.1 Procedure..................................................................................................................35
7.4 FINE-TUNING............................................................................................................................35
7.4.1 Procedure..................................................................................................................35
7.5 ADJUSTMENT FLOW CHART.......................................................................................................35
7.6 FINE-TUNING FLOW CHARTS.....................................................................................................41
7.6.1 Speed Setting fine-tuning..........................................................................................41
7.6.2 Fuel limit fine tuning...................................................................................................42
7.6.3 Clutch fuel limit fine tuning.........................................................................................43
8. ALARMS, DIAGNOSTICS AND SERIAL COMMUNICATIONS...........................................44
8.1 INTRODUCTION .........................................................................................................................44
8.1.1 Alarm indication and operation..................................................................................44
8.1.2 Serial interface........................................................................................................... 44
8.2 UG40-DI ALARM INDICATION AND OPERATION........................................................................... 44
8.2.1 Introduction................................................................................................................44
8.2.2 Explanation of the UG40-DI panel for alarms and diagnostics .................................44
8.2.3 Alarm flash codes...................................................................................................... 45
8.3 UG40-DI SERIAL INTERFACE ....................................................................................................46
8.3.1 Serial link with PC - alarm page ................................................................................46
8.3.2 Serial link with PC - parameter page.........................................................................46
8.3.3 Serial link with PC - uploading software.................................................................... 47
9. TROUBLESHOOTING AND REPAIRS.................................................................................49
9.1 INTRODUCTION .........................................................................................................................49
9.2 TROUBLESHOOTING (MECHANICAL AND ELECTRICAL) .................................................................49
9.2.1 Preliminary inspection ...............................................................................................49
9.2.2 Oil ..............................................................................................................................50
9.2.3 Compensating adjustment and needle valve ............................................................50
9.3 TROUBLESHOOTING CHART.......................................................................................................50
9.3.1 Definitions.................................................................................................................. 50
9.3.2 Trouble-shooting chart...............................................................................................51
9.4 GOVERNOR FIELD REPAIRS.......................................................................................................55
9.4.1 Removal of governor from engine.............................................................................55
9.5 RETURNING THE UG40-DI TO WOODWARD................................................................................56

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Table of Figures
FIGURE 1.1 OUTLINE DRAWING OF UG40-DI GOVERNOR.......................................................................4
FIGURE 3.1 DI CONTROL PANEL AND GOVERNOR DIAL PLATE................................................................7
FIGURE 3.2 SCHEMATIC DIAGRAM OF THE UG40-DI ..............................................................................9
FIGURE 4.1 RECOMMENDED OUTPUT SHAFT TRAVEL ADJUSTMENT...................................................... 17
FIGURE 4.2 OIL CHART...................................................................................................................... 19
FIGURE 4.3 OIL DRAIN PLUG.............................................................................................................. 20
FIGURE 4.4 UG40-DI ELECTRICAL CONNECTIONS.............................................................................. 21
FIGURE 8.1 EXAMPLE ALARM AND DIAGNOSTICS PAGE ....................................................................... 46
FIGURE 8.2 EXAMPLE UG40-DI PARAMETERS PAGE .......................................................................... 47
FIGURE 8.3 TYPICAL TERMINAL PROGRAM UPLOAD MESSAGES........................................................... 48
FIGURE 8.4 CHECKSUM FAILED MESSAGE .......................................................................................... 48

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Manual B03575.C UG40-DI Manual
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1. GENERAL INFORMATION
1.1 Introduction
This manual is applicable to the UG40-DI Governor and describes its mechanical and
electrical installation, operation and set-up. It is arranged in ten chapters:
- GENERAL INFORMATION
- ESD PROTECTION AND HANDLING
- DESCRIPTION
- INSTALLATION
- GOVERNOR MECHANICAL OPERATION AND ADJUSTMENTS
- CALIBRATION OF THE DIGITAL INTERFACE
- ADJUSTMENT OF THE DIGITAL INTERFACE
- ALARMS, DIAGNOSTICS AND SERIAL COMMUNICATIONS
- TROUBLESHOOTING AND REPAIRS.
Mechanical operation and adjustment of the UG40-DI is similar to that for the UG40
mechanical governor.
1.2 Description
The UG40-DI is a mechanical-hydraulic governor with a digital interface for controlling diesel
engines. The UG40-DI uses a 250 PSI oil supply and is mechanically linked to the fuel racks.
The maximum travel of the output (terminal) shaft is 38°, and the recommended travel of the
output shaft is 25° from no load to full load (refer to Section 4.5 for more details).
Normally, the UG40-DI operates isochronously (constant speed) regardless of load on the
engine, except during operation as described in Chapter 3. DESCRIPTION.
Speed droop is incorporated in the UG40-DI to divide and balance load between units driving
the same shaft or paralleled in an electrical system.
A load limit control is also a standard feature on the UG40-DI. It limits the amount of fuel
supplied by restricting the travel of the governor output shaft. An indicator dial shows the
governor output shaft limit position.
The load limit control may also be used for manually shutting down the engine.
1.3 System Compliance
This equipment complies with the relevant industry specifications and regulations.
1.4 General Safety Precautions
Obey the following safety precautions when you install the unit:
- Obey all cautions or warnings given in the procedures.
- Never bypass or override machine safety devices.
- Always use sufficient personnel and/or lifting equipment to move the UG40-DI.
1.5 Notes, Warnings and Cautions
The following examples show how notes, warnings and cautions are used in this manual:
☞Notes are used in the text to provide useful information or hints. This is a note.

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!
WARNING
Warnings are used when a procedure or action is dangerous and injury or death
might occur. This is a warning.
!
CAUTION
Cautions are used when a procedure or action can cause damage to equipment. This is a
caution.
1.6 Identification Plate
The identification plate is installed on the front of the governor. It contains the following
information:
- Part Number
- Serial number
- Manufacturing date
- Speed range
- Customer part number (if applicable).
Always give the part number and serial number in any correspondence with Woodward.
1.7 Technical Data
Governor pressure 1724 kPa (250 psi)
Weight Approx. 50 kg (110 lbs)
Work capacity 78 J (57.5 ft-lb)
Drive power requirement 0.37 kW (0.5 hp)
Output 38º
Oil capacity 7 liters
Speed range 350 - 1050 rpm (low speed), 550 - 1300 rpm (high speed)
Start Fuel Limit Duration Adjustable from 0-20 sec
Operating Temperature Range -20 to 93°C (-4 to 200°F)
Storage Temperature Range -40 to 100°C (-40 to 212°F)
Vibration Qualification Test
Specification Woodward RV2 (0.1 G2/Hz Random, 10-2000 Hz, 12.8 Grms, 3 hr per axis).
Shock Qualification Test
Specification 40 G, 11 msec saw-tooth pulse
Humidity Qualification Test
Specification Woodward H2 (60°C, 95% RH, 5 days)
IP level IP54
Steady state speed band 0.25 % of rated speed (under normal operating conditions)
Speed setting linearity 1 % over full range
Speed setting bandwidth 0.5 Hz for full range step (4 to 20mA and 20 to 4mA)
Power supply 24 Vdc nominal (18 - 32 Vdc), 25 watts (fused by 3A, slow)
Shutdown power 18 - 31 Vdc, 12 watts
Alarm signal output 17-31 Vdc, 100 mA, sourcing only
Standard governer drive shaft 1.125” diameter shaft with 48 SAE serrations
Optional governer drive shaft 0.625” diameter shaft with keyway 0.187” wide x 0.094” deep x 1.500” long for
gear held by 0.625”-18 castle nut
Terminal (output) shaft 0.750” diameter with 48 SAE serrations
1.8 Software Versions
At power-up for one time, the yellow Mode LED indicates the UG40-DI software version
using long flash pulses for the integer digit, and short flash pulses for the decimal digits. The
differences between the software versions are as follows:

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Software
version Description Mode LED flash pulse
3.07 Start fuel limit time = fixed 10 seconds. I….I….I….l.l.l.l.l.l.l
3.08 Start fuel limit time = fixed 20 seconds. I….I….I….l.l.l.l.l.l.l.l
4.01 I….I….I….l….l.l
4.02 Alarm and diagnostics functions.
Start fuel limit time = adjustable 0 to 20 seconds. I….I….I….l….l.l.l
I = 1 flash of Mode LED
…. = pause between flash pulses

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Figure 1.1 Outline Drawing of UG40-DI Governor (sheet 1 of 2)

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Figure 1.1 Outline Drawing of UG40-DI Governor (sheet 2 of 2)

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2. ESD PROTECTION AND HANDLING
!
CAUTION
All electronic equipment is static-sensitive, some components more than others. To protect
these components from static damage, you must take special precautions to minimize or
eliminate electrostatic discharges.
Follow these precautions when working with or near the control.
1. Before doing maintenance on the digital interface, discharge the static electricity on
your body to ground by touching and holding a grounded metal object (pipes,
cabinets, equipment, etc.).
2. Avoid the build-up of static electricity on your body by not wearing clothing made of
synthetic materials. Wear cotton or cotton-blend materials as much as possible
because these do not store static electric charges as much as synthetics.
3. Keep plastic, vinyl, and Styrofoam materials (such as plastic or Styrofoam cups, cup
holders, cigarette packages, cellophane wrappers, vinyl books or folders, plastic
bottles, and plastic ash trays) away from the control, the modules, and the work area
as much as possible.
4. Do not open the digital interface unless absolutely necessary. If you must open the
digital interface, follow these precautions:
- Do not touch any part of the printed circuit board.
- Do not touch the electrical conductors, the connectors, or the components with
conductive devices or with your hands.

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3. DESCRIPTION
3.1 Introduction
This Chapter describes the mechanical and digital interface parts of the UG40-DI governor.
The mechanical part is the same as the mechanical part on the UG Dial governor series.
3.2 DI Control Panel and Governor Dial Plate
Figure 3.1 DI Control Panel and Governor Dial Plate
3.3 Mechanical Governor
3.3.1 Introduction
Basic mechanical and hydraulic operation is similar for all UG governor types.
Along with the text, a schematic diagram, Figure 3.2, is provided as a visual means of
understanding the mechanical operation of the UG40-DI. This schematic shows a basic
design and does not include any auxiliary equipment.
3.3.2 Component description
Before describing UG40-DI operation, a brief description of the components will help you
understand its operation.

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3.3.2.1 Oil pump
The oil pump (14) provides oil pressure for the governor.
The pump gets its oil from the self-contained sump (15). The oil pump is a
positive-displacement gear pump with four check valves (13) for either direction of rotation.
One pump gear is part of the rotating bushing and the other is part of the laminated drive.
The rotating bushing is driven by the governor drive shaft, which is driven by the prime
mover. As the bushing rotates, it rotates the laminated drive. The oil pump gears can be
driven either clockwise or anticlockwise.
Oil flow is directed through the check valve system into the accumulator system (11).
3.3.2.2 Accumulator
The accumulator (11) stores oil under pressure for the operation of the UG40-DI governor.
The accumulator (two cylinders) also acts as a pressure-relief valve if oil pressure increases
above a set level.
The accumulator (11) consists of two spring-loaded pistons. Oil is pumped into the cylinders
and pressure is increased as the accumulator springs are compressed. When the oil
pressure exceeds 250 PSI, oil is released back to the sump through a relief port (12) in each
cylinder.
Oil flows from the accumulator through passages to the top of the power piston and to the
pilot valve system.
3.3.2.3 Power piston
The power piston (9) rotates the governor output shaft to the increase or decrease fuel
position.
The power piston is a differential type with oil pressure on both sides of the piston. The top
end of the power piston is connected to the governor output shaft (6) through a power lever
and link assembly.

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Figure 3.2 Schematic Diagram of the UG40-DI

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The bottom of the power piston has a larger area than the top of the piston. Therefore, less
oil pressure is needed on the bottom than on the top to maintain the piston stationary. If the
oil pressure is the same on both the top and bottom of the piston, the piston moves up to
rotate the governor output shaft in the increase fuel direction. The piston moves down only
when oil under the piston is released to sump.
Oil to and from the bottom of the power piston is regulated by the pilot valve system.
3.3.2.4 Pilot valve system
The pilot valve plunger and bushing controls the flow of oil to or from the bottom of the power
piston.
The pilot valve system includes the rotating bushing (38) and the pilot valve plunger (39).
The bushing (38) is rotated by the drive shaft (36) while the pilot valve plunger is held
stationary. Because of this rotation the friction between the pilot valve and bushing is
reduced. The pilot valve plunger has a control land that regulates oil flow through ports in the
bushing.
When the pilot valve plunger (39) is lowered, high-pressure oil flows under the power piston
(9), raising it. When the pilot valve plunger is raised, oil is released to sump from under the
power piston (9), lowering it. The higher pressure on top of the power piston (9), forces the
piston down. When the pilot valve plunger (39) is in its centred position, the control land
covers the control port as shown in the schematic, Figure 3.2, and there is no movement of
the power piston.
The movement of the pilot valve plunger (39) is controlled by the ballhead system (23) and
the dashpot compensation pistons (34) and (35).
3.3.2.5 Ballhead system
The ballhead system (23) senses speed changes of the prime mover compared to the speed
setting reference given by the speeder spring (25) and positions the pilot valve plunger (39).
The ballhead system includes a ballhead (23), flyweights (24), a speeder spring (25), a thrust
bearing (30), a speeder plug (29) and a speed setting rod (21).
As the governor drive shaft (36) rotates, the gear on the laminated drive (32) turns and
rotates the ballhead gears (23). The flyweights (24) are attached to the ballhead with pivot
pins, and a thrust bearing (30) rides on the toes of the flyweights (24). The speeder spring
(25) is held in position against the thrust bearing (30) by the speeder plug (29). The speeder
plug (29) is used to set a pressure on the speeder spring (25).
As the ballhead (23) rotates, the flyweights (24) pivot outward due to the centrifugal force. At
the same time the speeder spring (25) is forcing thrust bearing (30) downward on the
flyweight toes. This downward force is opposing the centrifugal force of the flyweights.
Increasing the drive speed increases the centrifugal force. Compressing the speeder spring
(25) with the speeder plug (29) increases the downward force applied to the flyweight toes,
and in turn, increases the governor speed setting. The prime mover must run faster to
generate a centrifugal force greater than the speeder spring force to balance the system
again.
Speeder spring (25) force or speed setting is controlled manually through the synchronizer
(speed setting) adjusting knob (5). It can also be controlled from the digital interface (see
3.4 Digital Interface). The speed setting is shown on the speed setting turns indicator (4).
3.3.2.6 Compensation system
The compensation system stabilizes the governor and obtains steady-state speed control.
Also, when correctly adjusted, the compensation system effectively regulates the amount of

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fuel necessary to bring the engine to the required output to adjust to a decrease or an
increase in load.
The compensation system creates a small temporary change of speed setting with governor
output shaft movement to produce a stabilizing speed droop characteristic in the governor.
The change of speed setting is followed by a slow return of speed setting to its original value.
Compensation is simply another word for temporary speed droop characteristic.
The compensation system includes a large dashpot compensation piston (34), a small
dashpot compensation piston (35), a floating lever (31), a compensation adjusting lever (22)
with a pivotable fulcrum (18), a compensation pointer (19) and a needle valve (33). See
Figure 3.2.
The large dashpot compensation piston (34) is connected to the governor output shaft (6) by
a compensation adjusting lever (22). A pivotable fulcrum (18) rides on the compensation
adjusting lever (22). Changing the fulcrum's (18) position allows the compensation lever (22)
to control the amount of stroke available for the large dashpot compensation piston (34).
The small dashpot compensation piston (35) is connected through a floating lever (31) to the
pilot valve plunger (39) and the speeder rod (21).
Moving the large dashpot compensation piston (34) down forces oil under the small dashpot
compensation piston (35). As the small dashpot compensation piston (35) is forced upward,
it lifts the pilot valve plunger (39) to close off the control port, which stops the flow of oil to the
bottom of the power piston (9).
The needle valve (33) is a variable orifice, which controls the flow of oil between both the
large (34) and the small dashpot compensation (35) pistons, and the oil sump.
☞Compensation must be properly adjusted to the particular engine and load to provide
stable operation (see Section 5.3.2 Compensation Adjustments).
3.3.2.7 Manual load limit control
The load limit control knob on the control plate hydraulically and mechanically limits the load
that can be placed on the engine by restricting the travel of the governor output shaft in the
increase fuel direction, and consequently the amount of fuel supplied to the engine.
The load limit control is also used for manually shutting down the engine by turning it to zero,
and for manual start limiting by moving the knob from 0 – 10 during engine start.
!
CAUTION
Do not manually force fuel rack linkage to increase fuel without first turning the load limit
control knob to 10, its maximum position. Failure to do so may cause damage and/or failure
of governor internal parts.
The load limit control consists of an indicator disc (7) geared to a load limit rack (8). The
control knob is also attached to the load limit cam (16).
Load is limited mechanically by positioning the load limit knob (cam 16). When the load
indicator reaches the preset point, the pilot valve plunger (39) is lifted, stopping any further
increase in fuel.
Turning the load limit control to zero to shut down the engine turns the cam (16) forcing the
load limit (shutdown) lever (20) and shutdown strap (17) down. As the right end of the load
limit (shutdown) lever (20) is forced downward, it pivots about its fulcrum and lifts the pilot
valve plunger (39), releasing oil from under the power piston (9). Pressure oil acting on top of
the power piston (9) forces it downward, rotating the governor output shaft (6) to minimum
fuel and causing the prime mover to shutdown.

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3.3.2.8 Manual speed setting knob
The speed setting knob is the speed adjusting control, and is used to change engine speed
for a single unit. On engines paralleled with other units, it is used to change engine load.
The lower knob, "SPEED SETTING INDICATOR", has no function of its own but has an
indicator disc which shows the number of revolutions of the speed setting knob.
3.3.3 Operation of the UG40-DI Mechanical Part
3.3.3.1 General Information
Refer to Figure 3.2 with the text to better understand the operation of the UG40-DI governor.
The description that follows is based upon speed changes caused by load changes and
speed droop.
3.3.3.2 Decrease in load
When the prime mover is running on speed, the flyweights (24) are in a vertical position for
normal steady state operation. The pilot valve plunger (39) is centred over the control port of
the rotating bushing, and the control land stops the flow of pressure oil through the bushing
(38) control port. There is no movement of the power piston (9), and no movement of the
governor output shaft (6).
When a decrease in load occurs and the same fuel setting is maintained, a decrease in load
creates an increase in speed. This generates the following sequence of governor
movements:
1. As speed increases, the centrifugal force of the flyweights (24) increases and
becomes stronger than the force of the speeder spring (25).
2. The flyweights (24) tip outward and raise the speeder rod (21) and the right end of
the floating lever (31).
3. This raises the pilot valve plunger (39) opening the control port in the rotating
bushing (38). Oil is released from the bottom of the power piston (9) to sump.
4. Pressure oil on the top side of the power piston (9) moves it downward rotating the
governor output shaft in the decrease fuel direction.
5. Linkage from the governor output shaft (6) lowers the compensation adjusting lever
(22), which rotates at the fulcrum (18), raising the large dashpot compensation
piston (34).
6. Suction is thus applied to the chamber of the small dashpot compensation piston
(35), lowering the left end of the floating lever (31).
7. This towers the pilot valve plunger (39) closing the control port (37).
8. As sump oil flows through the needle valve (33) from the sump into the dashpot
compensation piston assembly (34 and 35) the small dashpot compensation piston
(35) is returned to its normal centred position by the compensation spring, at the
same rate as the speeder rod (21). This keeps the pilot valve plunger (39) in its
centred position.
9. The control port in the rotating bushing (38) is kept closed by the land on the pilot
valve plunger (39).
10. This stops the governor output shaft and power piston movement in the new
decreased fuel position. This is the position needed to run the prime mover at the
selected speed setting with the new load.
3.3.3.3 Increase in load
When the prime mover is running on speed, the flyweights (24) are in a vertical position and
the pilot valve plunger (39) is in its centred position. There is no movement of the power
piston, and no movement of the governor output shaft.

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When an increase in load occurs and the same fuel setting is maintained, an increase in load
creates a decrease in speed. This generates the following sequence of governor
movements:
1. As speed decreases, the centrifugal force of the flyweights (24) decreases and the
opposing speeder spring (25) force is now greater than the centrifugal force of the
flyweights (24).
2. The flyweights (24) tip inward and lower the speeder rod (21) and the right end of the
floating lever (31).
3. This lowers the pilot valve plunger (39) opening the control port in the rotating
bushing (38). Pressure oil is released through the control port into the lower cylinder
of the power piston (9).
4. The power piston is forced upward by the pressure oil acting on the larger lower
surface area of the power piston, and the governor output shaft is rotated in the
increase fuel direction.
5. Linkage from the governor output shaft (6) lifts the compensating adjusting lever
(22), which rotates at the fulcrum (18), lowering the large dashpot compensation
piston (34).
6. Pressure oil is applied to the bottom side of the small dashpot compensation piston
(35), raising the left end of the floating lever (31).
7. This raises the pilot valve plunger (39) closing the control port (37).
8. As pressure oil flows through the needle valve (33) from the dashpot compensation
piston assembly (34 and 35), the small dashpot compensation piston (35) is returned
to its normal centred position by the compensation spring, at the same rate as the
speeder rod (21). This keeps the pilot valve plunger (39) in its centred position.
9. The control port in the rotating bushing (38) is kept closed by the land on the pilot
valve plunger (39).
10. This stops the governor output shaft and power piston movement in the new
increased fuel position. This is the position needed to run the prime mover at the
selected speed setting with the new load.
In both cases, a decrease or an increase in load, the compensation system operates in
opposite directions.
The compensation or amount of movement of the large dashpot compensation piston (34) is
controlled by the compensation adjustment, that is, the position of the fulcrum (18).
The rate at which the small dashpot compensation piston (35) is returned to normal is
controlled by the needle valve adjustment, that is, the rate of flow of oil through the needle
valve (33).
3.3.3.4 Speed droop
Droop is used to divide and balance load between units driving the same shaft or paralleled
in the electrical system.
Droop is the decrease in speed taking place when the governor output shaft moves from the
minimum to the maximum fuel position in response to a load increase, expressed as a
percentage of rated speed.
If instead of a decrease in speed, an increase takes place, the governor is showing a
negative droop. Negative droop will cause instability in a governor. This is caused by
incorrect adjustment.
Not enough droop can cause instability in the form of hunting, surging or difficulty in
response to a load change. Too much droop can result in slow governor response in picking
up or dropping off a load.
Using an example where the governor speed is 1500 RPM at no load and 1450 RPM at full
load, droop can be calculated with the formula:

UG40-DI Manual Manual B03575.C
14 Woodward
%Droop = No load speed - Full load speed
Full load speed
%Droop = 1500 rpm - 1450 rpm
x 100
x 100
1450 rpm = 3.5%
If the decrease in speed is greater than 50 RPM when the governor output shaft moves from
the minimum to the maximum fuel position, droop greater than 3.5% is shown by the
governor. If the decrease in speed is less than 50 RPM, droop less than 3.5% is shown by
the governor.
☞If the governor output shaft does not use the full 30° of available travel from "NO LOAD” to
"FULL LOAD, " droop will also be reduced proportionally.
Marks on the droop adjustment scale on the dial panel are reference numbers only, and do
not represent droop percentages. Thus the 100 mark does not represent 100% droop. It
represents the maximum droop percentage available on that particular UG40-DI governor
model.
The speed droop control consists of a control knob, cam, and linkage (27) connected by a
sliding fulcrum (26) to the speed droop lever (3). A speeder screw (28) connects the speed
droop lever to the speeder plug (29). When speed droop is preset, the compression of the
speeder spring (25) changes as the output shaft rotates. Increasing the fuel reduces speeder
spring compression and in turn the governor speed setting. The unit gradually reduces its
speed as load is applied. This relationship between load and speed acts as a resistance to
load changes when the unit is in parallel with other engines.
Reducing droop to zero allows the unit to change load without changing speed. Normally, set
zero droop on units running alone. On in-parallel units, set the least amount of droop
possible to provide satisfactory load division.
For AC generating units tied in with other units, set droop sufficiently high (reference
numbers 30 to 50 on the dial) to prevent interchange of load between units. If one unit in the
system has enough capacity, set its governor on zero droop and it will regulate the frequency
of the prime mover system. If its capacity is not exceeded this unit will handle all load
changes.
Operate the Speed Setting Knob after setting the droop to return to the original RPM. With
parallel engines, operate the Speed Setting Knob to distribute load between units.
3.4 Digital Interface
3.4.1 Introduction
The following functions of the UG40-DI are built into the DI part:
1. Speed setting
The following speed settings are available:
- 4 – 20 mA remote speed reference
- Discrete fixed speed input
- Discrete raise/lower speed input.
2. Speed up and down ramp
There are four different ramp-rates in the DI:
- Two adjustable ramp rates for the raise and lower discrete inputs
- One adjustable ramp rate for the 4 – 20 mA raise speed setting
- One fixed ramp rate for the 4 – 20 mA lower speed setting.