Introduction

NOTE: For Specifications with illustrations, make reference to SPECIFICATIONS for 3304B & 3306B GENERATOR SET ENGINE ATTACHMENTS, Form No. SENR2798. If the Specifications in Form SENR2798 are not the same as in the Systems Operation and the Testing and Adjustment, look at the printing date on the back cover of each book. Use the Specifications given in the book with the latest date.

Fuel System

Fuel Ratio Control

FUEL RATIO CONTROL (Engine Started)
1. Inlet air chamber. 2. Diaphragm assembly. 3. Internal valve. 4. Oil drain passage. 5. Oil Inlet. 6. Stem. 7. Spring. 8. Piston. 9. Oil passage. 10. Oil chamber. 11. Lever.

FUEL RATIO CONTROL (Control Activated)
1. Inlet air chamber. 2. Diaphragm assembly. 3. Internal valve. 4. Oil drain passage. 5. Oil inlet. 6. Stem. 7. Spring. 8. Piston. 9. Oil passage. 10. Oil chamber. 11. Lever.

The fuel ratio control limits the amount of fuel to the cylinders during an increase of engine speed (accleration) to reduce exhaust smoke.

Stem (6) moves lever (11) which will restrict the movement of the fuel rack in the FUEL ON direction only.

With the engine stopped, stem (6) is in the fully extended position. The movement of the fuel rack and lever (11) is not restricted by stem (6). This gives maximum fuel to the engine for easier starts.

After the engine is started, engine oil flows through oil inlet (5) into pressure oil chamber (10). From oil chamber (10) oil flows through oil passage (9) into internal valve (3) and out oil drain passages in stem (6).

Stem (6) will not move until inlet manifold pressure increases enough to move internal valve (3). A line connects the inlet manifold with inlet air chamber (1) of the fuel ratio control.

When inlet manifold pressure increases, it causes diaphragm assembly (2) to move toward the right. This also causes internal valve (3) to move to the right. When internal valve (3) moves to the right, it closes oil passage (9).

When oil passage (9) is closed, oil pressure increases in oil chamber (10). Oil pressure moves piston (8) and stem (6) to the left and into the operating position. The fuel ratio control will remain in the operating position until the engine is shut off.

When the governor control is moved to increase fuel to the engine, stem (6) limits the movement of lever (11) in the FUEL ON direction. The oil in oil chamber (10) acts as a restriction to the movement of stem (6) until inlet air pressure increases.

As the inlet air pressure increases, diaphragm assembly (2) and internal valve (3) move to the right. The internal valve opens oil passage (9), and oil in oil chamber (10) goes to oil drain passage (4). With the oil pressure reduced behind piston (8), spring (7) moves the piston and stem (6) to the right. Piston and stem (8 and 6) will move until oil passage (9) is closed by internal valve (3). Lever (11) can now move to let the fuel rack go to the full fuel position. The fuel ratio control is designed to restrict the fuel until the air pressure in the inlet manifold is high enough for complete combustion. It prevents large amounts of exhaust smoke caused by an air fuel mixture with too much fuel.

FUEL RATIO CONTROL (Engine Acceleration)
1. Inlet air chamber. 2. Diaphragm assembly. 3. Internal valve. 4. Oil drain passage. 5. Oil Inlet. 6. Stem. 7. Spring. 8. Piston. 9. Oil passage. 10. Oil chamber. 11. Lever.

Woodward PSG Governors

SCHEMATIC OF LATEST PSG GOVERNOR
1. Return spring. 2. Output shaft. 3. Output shaft lever. 4. Strut assembly. 5. Speeder spring. 6. Power piston. 7. Flyweights. 8. Needle valve. 9. Thrust bearing. 10. Pilot valve compensating land. 11. Buffer piston. 12. Pilot valve. 13. Pilot valve bushing. 14. Control ports. A. Chamber. B. Chamber

Introduction

The Woodward PSG (Pressure compensated Simple Governor) can operate as an isochronous or a speed droop type governor. It uses engine lubrication oil, increased to a pressure of 175 psi (1200 kPa) by a gear type pump inside the governor, to give hydra/mechanical speed control.

Pilot Valve Operation

The fuel injection pump camshaft drives a governor drive unit. This unit turns pilot valve bushing (13) clockwise as seen from the drive unit end of the governor. The pilot valve bushing is connected to a spring driven ballhead. Flyweights (7) are fastened to the ballhead by pivot pins. The centrifugal force caused by the rotation of the pilot valve bushing causes the flyweights to pivot out. This action of the flyweights changes the centrifugal force to axial force against speeder spring (5). There is a thrust bearing (9) between the toes of the flyweights and the seat for the speeder spring. Pilot valve (12) is fastened to the seat for the speeder spring. Movement of the pilot valve is controlled by the action of the flyweights against the force of the speeder spring.

The engine is at the governed (desired) rpm when the axial force of the flyweights is the same as the force of compression in the speeder spring. The flyweights will be in the position shown. Control ports (14) will be closed by the pilot valve.

Fuel Increase

When the force of compression in the speeder spring increases (operator increases desired rpm) or the axial force of the flyweights decreases (load on the engine increases) the pilot valve will move in the direction of the drive unit. This opens control ports (14). Pressure oil flows through a passage in the base to chamber (B). The increased pressure in chamber (B) causes power piston (6) to move. The power piston pushes strut assembly (4), that is connected to output shaft lever (3). The action of the output shaft lever causes clockwise rotation of output shaft (2). This moves fuel control linkage (15) in the FUEL ON direction.

PSG GOVERNOR INSTALLED
2. Output shaft. 15. Fuel control linkage.

As the power piston moves in the direction of return spring (1) the volume of chamber (A) increases. The pressure in chamber (A) decreases. This pulls the oil from the chamber inside the power piston, above buffer piston (11) into chamber (A). As the oil moves out from above buffer piston (11) to fill chamber (A) the buffer piston moves up in the bore of the power piston. Chambers (A and B) are connected respectively to the chambers above and below the pilot valve compensating land (10). The pressure difference felt by the pilot valve compensating land adds to the axial force of the flyweights to move the pilot valve up and close the control ports. When the flow of pressure oil to chamber (B) stops so does the movement of the fuel control linkage.

Fuel Decrease

When the force of compression in the speeder spring decreases (operator decreases desired rpm) or the axial force of the flyweights increases (load on the engine decreases) the pilot valve will move in the direction of speeder spring (5). This opens control ports (14). Oil from chamber (B) and pressure oil from the pump will dump through the end of the pilot valve bushing. The decreased pressure in chamber (B) will let the power piston move in the direction of the drive unit. Return spring (1) pushes against strut assembly (4). This moves output shaft lever (3). The action of the output shaft lever causes counterclockwise rotation of output shaft (2). This moves fuel control linkage (15) in the FUEL OFF direction.

PSG GOVERNOR
6. Power piston. 8. Needle valve. 10. Pilot valve compensating land. 11. Buffer piston. 14. Control ports. A. Chamber. B. Chamber.

As power piston (6) moves in the direction of the drive unit the volume of chamber (A) decreases. This pushes the oil in chamber (A) into the chamber above buffer piston (11). As the oil from chamber (A) flows into the power piston it moves the buffer piston down in the bore of the power piston. The pressure at chamber (A) is more than the pressure at chamber (B). Chambers (A and B) are connected respectively to chambers above and below the pilot valve compensating land (10). The pressure difference felt by the pilot valve compensating land adds to the force of the speeder spring to move the pilot valve down and close the control ports. When the flow of oil from chamber (B) stops so does the movement of the fuel control linkage.

Hunting

There is a moment between the time the fuel control linkage stops its movement and the time the engine actually stops its increases or decrease of rpm. During this movement there is a change in two forces on the pilot valve, the pressure difference at the pilot valve compensating land and the axial force of the flyweights. The axial force of the flyweights changes until the engine stops its increase or decrease of rpm. The pressure difference at the pilot valve compensating land changes until the buffer piston returns to its original position. A needle valve (8) in a passage between space (A) and (B) controls the rate at which the pressure difference changes. The pressure difference makes compensation for the axial force of the flyweights until the engine stops it increase or decrease of rpm. If the force on the pilot valve compensating land plus the axial force of the flyweights is not equal to the force of the speeder spring the pilot valve will move. This movement is known as hunting (movement of the pilot valve that is not the result of a change in load or desired rpm of the engine).

The governor will hunt each time the engine actually stops its increase or decrease of rpm at any other rpm than that desired. The governor will hunt more after a rapid or large change of load or desired rpm than after a gradual or small change.

PSG GOVERNOR
8. Needle valve

NOTE: The Woodward PSG Governor is removed from the engine to show the needle valve (8). When the governor is installed on the engine, the needle valve (8) is between the governor and the cylinder block.

Speed Adjustment

PSG governors use a clutch assembly (2) driven by a 110V AC/DC or 24V DC reversible synchronizing motor (1) to move link assembly (3) up or down. The clutch assembly protects the motor if the adjustment is run against the stops. The motor is controlled by a switch that is remotely mounted. The clutch assembly can be turned manually if necessary.

PSG GOVERNOR
1. Synchronizing motor. 2. Clutch assembly. 3. Link assembly.

Speed Droop

Speed droop is the difference between no load rpm and full load rpm. This difference in rpm divided by the full load rpm and multiplied by 100 is the percent of speed droop.

The speed droop of the PSG governor can be adjusted by movement of an adjustment lever on the outside of the governor that is connected to pivot pin (2) by link (4). The governor is isochronous when it is adjusted so that the no load and full load rpm is the same. Speed droop permits load division between two or more engines that drive generators connected in parallel or generators connected to a single shaft.

PSG GOVERNOR
1. Bracket. 2. Pivot pin. 3. Output shafts.

Speed droop adjustment on PSG governors is made by movement of pivot pin (2). When the pivot pin is put in alignment with the output shafts, movement of the output shaft lever will not change the force of the speeder spring. When the force of the speeder spring is kept constant the desired rpm will be kept constant. See PILOT VALVE OPERATION. When the pivot pin is moved out of alignment with the output shafts, movement of the output shaft lever will change the force of the speeder spring proportional to the load on the engine. When the force of the speeder spring is changed the desired rpm of the engine will change.

PSG GOVERNOR
2. Pivot pin. 4. Link.

Electrical System Attachments

Instrument Panel

WIRING DIAGRAM FOR INSTRUMENT PANEL
1. Light switch. 2. Panel lights. 3. Instrument panel. 4. Ammeter. 5. Oil pressure gauge. 6. Water temperature gauge. 7. Gear oil pressure gauge (not used on Gen.Set engines). 8. Terminal strip. 9. Wire to battery. 10. Oil pressure switch with time delay. 11. Sending unit for oil pressure. 12. Sending unit for water temperature. 13. Sending unit for gear oil pressure (not used on Gen.Set engines).

GAUGES WITH RESISTORS FOR 32 VOLT SYSTEM
1. Resistor. 2. 0 to 80 psi oil pressure gauge. 3. Resistor. 4. 100° to 240°F water temperature gauge. 5. Resistor (not used on Gen.Set engines). 6. 0 to 300 psi gear oil pressure gauge (not used on Gen.Set engines).

Electrical Gauges And Sending Units

The electrical gauges and sending units operate in electrical balance. Because of this, the voltage and resistance ratings are important to get the correct indications on the gauges. The chart shows components that operate together.

Sending Unit for Water Temperature

SENDING UNIT FOR WATER TEMPERATURE
1. Connection. 2. Bushing. 3. Bulb.

The sending unit for water temperature is an electrical resistance. It changes the value of its resistance according to the temperature which the bulb (3) feels.

The sending unit is in a series circuit with the electrical gauge. When the temperature is high, the resistance is high. This makes the gauge have a high reading.

The sending unit must be in contact with the coolant. If the coolant level is too low because of a sudden loss of coolant while the engine is running or because the level is too low before starting the engine, the sending unit will not work correctly.

Sending Unit for Oil Pressure

SENDING UNIT FOR OIL PRESSURE
1. Connection. 2. Bushing.

The sending unit for oil pressure is an electrical resistance. It has a material which changes electrical resistance according to pressure which it feels.

The sending unit for oil pressure is in a series circuit with the electrical gauge. As the pressure on the sending unit changes, the reading on the gauge changes in the same way.

Electric Hour Meter

WIRING DIAGRAM FOR ELECTRIC HOUR METER
1. Electrical hour meter. 2. Pressure switch. 3. To alternator or battery.

The electric hour meter (1) measures the clock hours that the engine operates. The electric hour meter (1) activates when the pressure switch (2) closes. The pressure switch (2) closes the circuit from the positive terminal on the alternator or battery when the engine oil pressure is above approximately 6 psi (40 kPa).

Electric Tachometer Wiring

1. Magnetic pickup. 2. Terminal Connections - terminals 7 and 8 on standby governor control. 3. Tachometer. 4. Ground connection - governor control chassis ground. 5. Governor control terminal strip. 6. Wiring connections - for second tachometer circuit if needed. 7. All wire must be 22AWG shielded cable or larger. 8. Dual speed switch terminal strip. 9. Ground connection - ground to engine.

Wiring Diagram

STARTING AND CHARGING SYSTEM
1. Off, Start Switch. 2. Ammeter. 3. Fuel shutoff solenoid. 4. Starter solenoid. 5. Alternator regulator. 6. Starter motor. 7. Pressure switch (normally open). 8. Alternator. 9. Battery. 10. Hourmeter.

Automatic Start/Stop System (Non-Package Generator Sets)

AUTOMATIC START/STOP SYSTEM SCHEMATIC (Hydraulic Governor)
1. Starter motor and solenoid. 2. Shutoff solenoid. 3. Fuel pressure switch. 4. Water temperature switch. 5. Oil pressure switch. 6. Overspeed contactor. 7. Battery. 8. Low lubricating oil pressure light (OPL). 9. Overcrank light (OCL). 10. Overspeed light (OSL). 11. High water temperature light (WTL). 12. Automatic control switch (ACS).

An automatic start/stop system is used when a standby electric set has to give power to a system if the normal (commercial) power supply has a failure. There are three main sections in the system. They are: the automatic transfer switch, the start/stop control panel (part of switch gear) and the electric set.

Automatic Transfer Switch

The automatic transfer switch normally connects the 3-phase normal (commercial) power supply to the load. When the commercial power supply has a failure the switch will transfer the load to the standby electric set. The transfer switch will not transfer the load from commercial to emergency power until the emergency power gets to the rated voltage and frequency. The reason for this is, the solenoid that causes the transfer of power operates on the voltage from the standby electric set. When the normal power returns to the rated voltage and frequency and the time delay (if so equipped) is over, the transfer switch will return the load to the normal power supply.

AUTOMATIC TRANSFER SWITCH (ATS)
1. E1, E2 and E3 input to ATS from emergency source. 2. N1, N2 and N3 input to ATS from normal source. 3. T1, T2 and T3 output from ATS to the load. 4. Transfer mechanism.

Control Panel

The main function of the control panel is to control the start and shutoff of the engine.

AUTOMATIC START/STOP CONTROL PANEL
1. Overcrank light (OCL). 2. Low lubricating oil pressure light (OPL). 3. Overspeed light (OSL). 4. Automatic control switch (ACS). 5. High water temperature light (WTL).

The engine control on the automatic start/stop control panel is an automatic control switch (ACS) with four positions. The positions of switch (4) are: OFF/RESET, AUTO. MAN and STOP. Each light (1), (2), (3) and (5) goes ON only when a not normal condition in the engine stops the engine. The light for the condition in the engine that stopped the engine is ON even after the engine has stopped. Switch (4) must be moved to the OFF/RESET position for the light to go OFF. Each light will go ON, for a light test, when the light is pushed in and held in.

When the generator is to be used as a standby electric power unit, the automatic control switch is put in the AUTO position. Now, if the normal (commercial) electric power stops, the engine starts and the generator takes the electric load automatically. When the normal (commercial) electric power is ON again, for the electric load, the circuit breaker for the generator electric power automatically opens and the generator goes off the electric load. After the circuit breaker for the generator opens, the engine automatically stops.

When the automatic control switch (ACS) is moved to the MAN position, the engine starts. It is now necessary for the circuit breaker for the generator electric power to be closed manually. If the generator is a standby electric power unit and the automatic control switch (ACS) is in the MAN position when normal (commercial) electric power is ON again, the generator circuit breaker opens and the engine stops automatically the same as when the switch (ACS) is in the AUTO position.

The engine will stop with the automatic control switch (ACS) in either the AUTO or MAN positions if there is not normal condition in the engine. The not normal condition in the engine that can stop the engine is either low lubricating oil pressure, high engine coolant (water) temperature or engine overspeed (too much rpm). When any of these conditions stops the engine, the light for the not normal condition will stay ON after the engine is stopped. The fourth not normal condition light is ON only when the starter motor runs the amount of seconds for the overcrank timer (engine does not start).

Move the automatic control switch (ACS) to the OFF/RESET position and the not normal condition lights go OFF.

Electric Set

The components of the electric set are: the engine, the generator, the starter motor, the battery, the shutoff solenoid and signal switches on the engine. The electric set gives emergency power to drive the load.

An explanation of each of the signal components is given in separate topics.

Wiring Diagrams

The following wiring diagrams are complete to show the connections of the automatic start/stop components with the engine terminal strip (TS1). The diagrams show all available options for both the hydraulic governor application or the PSG Governor application.

For a more complete explanation of operation of the automatic start/stop system, refer to Floor Standing Switchgear Form No. SENR7970.

Automatic Start/Stop Wiring

Component Abbreviations

NOTE A: Terminals 13 and 14 of the generator box will be connected to terminals 13 and 14 of the control panel when the CDT is not supplied.

NOTE B: Red jumper wire from terminal strip point number 4A to 4 in control panel must be removed when the cycle cranking module (CCM) is used.

NOTE C: Auxiliary relay (ARX) contacts are to be customer wired. See Relay Contact Schematic.

NOTE D: Dotted lines shown on Control Panel Wiring Schematic show engine wiring.

NOTE E: The overcrank timer (OCT) is to be adjusted to the 30 second setpoint (red dot). When cycle cranking (CCM) is used, the overcrank timer (OCT) is to be adjusted to the 90 second setpoint 9 (white dot).

NOTE F: ACS switch contacts shown with switch in auto position.

NOTE G: Jumper wire from terminal 72 to terminal 73 must be removed when DC ammeter (A) is used.

NOTE H: Jumper wire from terminal 13 to terminal 133 to be removed if additional fault shutdowns are added. Examples: reverse power relay or remote shutdown. Insert a normally closed switch between terminal 13 and terminal 133.

CONTROL PANEL WIRING SCHEMATIC

Automatic Start/Stop Wiring For Non-Package Generator Set (Used with Hydramechanical or Woodward PSG Governors)

For wire sizes and color codes see the chart at the front of Wiring Diagrams section.

Wires and cables shown in dotted lines are customer supplied wiring.

STARTING SYSTEM WITH ONE STARTER MOTOR
1. Magnetic switch. 2. Circuit breaker. 3. Starter motor. 4. Battery. 5. Circuit breaker. 6. Terminal strip (on engine).

DUAL SPEED SWITCH
7. Magnetic pickup. 8. Dual speed switch. 9. Time delay relay. 10. Oil pressure switch. 11. Governor synchronizing motor. 12. Water temperature switch.

SHUTOFF SOLENOID
13. Circuit breaker. 14. Rack shutoff solenoid. 15. Diode.

AUTOMATIC START/STOP SYSTEM SCHEMATIC

Electric Shutoff And Alarm System

Introduction

There are three types of electrical protection systems available for the 3300 Generator Set Engines.

1. Oil Pressure and Water Temperature Protection.

2. Oil Pressure, Water Temperature and Overspeed Protection.

3. Automatic Start/Stop Systems.

a. Package Generator Set

b. Non-Package Generator Set

This manual has information for No. 1 and 2. Make reference to the Generator manual and the Switchgear manual for information for No. 3.

The electric shutoff system is designed to give protection to the engine if there is a problem or a failure in any of the different engine systems. The engine systems that are monitored are: engine overspeed, starter motor crank terminate, engine oil pressure and engine coolant temperature.

The electric protection system consists of the electronic speed switch and time delay relay. This system monitors the engine from starting through rated speed.

Dual Speed Switch (DSS) - The speed switch has controls (in a single unit) to monitor engine overspeed and crank terminate speed.

Engine Overspeed - An adjustable engine speed setting (normally 118% of rated speed) that gives protection to the engine from damage if the engine runs too fast. This condition will cause a switch to close that shuts off the fuel to the engine.

Crank Terminate (Starter Motor) - An adjustable engine speed setting that gives protection to the starter motor from damage by overspeed. This condition will cause a switch to open that stops current flow to the starter motor circuit. The starter motor pinion gear will then disengage from engine flywheel ring gear. The crank terminate can also be used to activate the time delay relay.

Time Delay Relay - This relay has special ON/OFF switches with two controls that will either make the relay activate immediately, or after a 9 second delay. The time delay relay is used to arm the shutdown system. The time delay relay has a 70 second delay to be sure of complete engine shutdown and to prevent damage to the shutoff solenoids.

Water Temperature Contacter Switch - This contactor switch is a separate unit (mounted in the water manifold) that is wired into the shutdown circuit. It has an element that feels the temperature of the coolant (it must be in contact with the coolant). When the engine coolant temperature becomes too high, the switch closes to cause the fuel to be shut off to the engine.

Engine Oil Pressure Switch - This switch is mounted at the rear of the engine and feels the pressure of the oil in the oil manifold. The oil pressure switch is used to determine low engine oil pressure and to activate the time delay relay.

Wiring Diagrams - Abbreviations, wire codes and recommended wire sizes, used with the wiring diagrams that follow, can be found at the front of the WIRING DIAGRAMS SECTION.

The notes that follow are used with the wiring diagrams shown in this section.

CUSTOMER TO FURNISH BATTERY AND ALL WIRES SHOWN DOTTED

NOTE A: Optional ground to engine may be used with grounded systems only.

NOTE B: These leads terminate at the starter motor and must be omitted when there is no starter motor. In this case customer must provide DC power at the other termination point of these two leads.

NOTE C: If 2301 Governor is used, only one magnetic pickup is required. Use magnetic pickup from overspeed group. Wire magnetic pickup to speed switch. Then wire from speed switch to the 2301 Governor. The speed switch may be installed physically near the 2301 if desired.

NOTE D: Electronic dual speed switch and electronic time delay relay can be wired to battery power continuously since the system will draw less than 40 MA current when the engine is not running.

NOTE E: If required, customer is to supply (RNS) Remote Normal Shutdown Switch. Requires a single pole N.O. switch with a minimum contact rating of 5 amps inductive at the charging system voltage. Can be a latching switch if customer prefers. Shuts off engine fuel when activated.

NOTE F: If required, customer is to supply (RESS) Remote Emergency Shutdown Switch. Requires a single pole N.O. switch with a minimum contact rating of 5 amps inductive at the charging system voltage. Can be latching switch if customer prefers. Shuts off engine air and fuel when activated. This shut-off mode must not be used for normal engine shutdown.

Water Temperature And Oil Pressure Shutoff System (With Time Delay Relay)

WIRING DIAGRAM (Fuel Shutoff Solenoid Energized to Shutoff)
1. Time delay relay. 2. Oil pressure switch. 3. Water temperature switch. 4. Switch (N.O.). 5. Circuit breaker. 6. Shutdown relay. 7. Battery. 8. Diode assembly. 9. Shutoff solenoid. 10. Starter motor.

When the engine starts, engine oil pressure will close the N.O. switch and open the N.C. switch in oil pressure switch (2). This completes the circuit to time delay relay (1). N.O. switch (4) in the time delay relay now closes and completes the circuit between shutdown relay (6) and terminal TD-7 of the time delay relay.

If the engine coolant temperature goes above the setting of water temperature switch (3), the N.O. contacts will close. This lets current flow through water temperature switch (3) and through switch (4) to activate shutdown relay (6) which in turn activates fuel shutoff solenoid (9). When the engine stops, engine oil pressure will become less than the setting of the oil pressure switch. The N.O. switch will open and stop the flow of current to the time delay relay. This will start the time delay relay timer. After 70 seconds, switch (4) will open to stop current flow through shutdown relay (6). Now, fuel shutoff solenoid (9) will no longer be activated.

If engine oil pressure gets less than the setting of the oil pressure switch, the N.C. switch will close. This will let current flow through switch (4) to activate shutdown relay (6) which in turn activates fuel shutoff solenoid (9). The N.O. switch will open and start the time delay relay timer. After 70 seconds, switch (4) will open to stop current flow through shutdown relay (6). Now, fuel shutoff solenoid (9) will no longer be activated.

Water Temperature, Oil Pressure And Electronic Overspeed Shutoff System (With Time Delay Relay)

WIRING DIAGRAM (Fuel Shutoff Solenoid Energized to Shutoff)
1. Magnetic pickup. 2. Dual speed switch. 3. Overspeed switch. 4. Crank terminate switch. 5. Water temperature switch. 6. Oil pressure switch. 7. Time delay relay. 8. Switch (N.O.). 9. Shutdown relay. 10. Battery. 11. Diode assembly. 12. Shutoff solenoid. 13. Starter motor.

The engine speed is felt by magnetic pickup (1). As the teeth of the flywheel go through the magnetic lines of force around the pickup, an AC voltage is made. Dual speed switch (2) measures engine speed from the frequency of the voltage.

Time delay relay (7) controls the operation of shutdown relay (9), which in turn, controls the operation of fuel shutoff solenoid (12). Time delay relay (7) will keep the fuel shutoff solenoid energized for 70 seconds after a fault condition. This prevents the engine from being started again before the flywheel has stopped rotation.

When the engine starts and gets to a speed just above cranking speed, the normally open contacts of crank terminate switch (4) [which is part of dual speed switch (2)] will close. This will complete the circuit to time delay relay (7) through terminal TD-2. In approximately 9 seconds N.O. switch (8) in time delay relay (7) will close and complete the circuit between shutdown relay (9) and terminal TD-7 of the time delay relay. If the engine oil pressure has not activated oil pressure switch (6) by 9 seconds, current will flow through the N.C. switch in the oil pressure switch and through the now closed N.O. switch (8) to activate shutdown relay (9) which in turn activates fuel shutoff solenoid (12). If engine oil pressure activates oil pressure switch (6), the N.O. switch will close and the N.C. switch will open. This will let current flow to terminal TD-1 of the time delay relay and immediately close N.O. switch (8). At the same time the N.C. switch in the oil pressure switch will open and prevent current flow to switch (8).

If the engine speed increases above the overspeed setting (118% of rated speed) of the dual speed switch, the overspeed switch (part of the dual speed switch) will close across terminals DSS-7 and DSS-8. This completes the circuit to shutdown relay (6) through the now closed switch (8) at terminal TD-7. Shutdown relay (9) is activated and in turn activates fuel shutoff solenoid (12) to cause the engine to shutdown.

When the engine speed gets less than the cranking speed setting, switch (4) opens. This stops the flow of current to terminal TD-2 of the time delay relay. When the engine stops, engine oil pressure will become less than the setting of the oil pressure switch. The N.O. switch will open and stop the flow of current to terminal TD-1 of the time delay relay. This will start the time delay relay timer. After 70 seconds, switch (8) will open and stop current flow to shutdown relay (9) and fuel shutoff solenoid (12) will no longer be activated.

After an overspeed shutdown, a button on the dual speed switch must be pushed to open the overspeed switch before the engine will run.

When the engine has been started and is running, the time delay relay will close switch (8). If the engine coolant temperature goes above the setting of water temperature switch (5), the N.O. contacts will close. This lets current flow through the water temperature switch and through switch (8) to activate shutdown relay (9) and in turn activates fuel shutoff solenoid (12).

When the engine speed gets less than the cranking speed setting, switch (4) opens. This stops the flow of current to terminal TD-2 of the time delay relay. When the engine stops, engine oil pressure will become less than the setting of the oil pressure switch. The N.O. switch will open and stop the flow of current to terminal TD-1 of the time delay relay. This will start the time delay relay timer. After 70 seconds, switch (8) will open and stop current flow to shutdown relay (9) and fuel shutoff solenoid (12) will no longer be activated.

When the engine has been started and is running, the time delay relay will close switch (8). If the engine oil pressure gets less than the setting of oil pressure switch (6), the N.C. switch will close. This will let current flow through switch (8) to activate shutdown relay (9) and in turn activates fuel shutoff solenoid (12). The N.O. switch will also open and stop current flow to terminal TD-1 of the time delay relay. When the engine speed gets less than the cranking speed setting, switch (4) opens. This stops the flow of current to terminal TD-2 of the time delay relay and starts the time delay relay timer. After 70 seconds, switch (8) will open and stop current flow to shutdown relay (9) and fuel shutoff solenoid (12) will no longer be activated.

Electronic Overspeed Shutoff System (With Time Delay Relay)

WIRING DIAGRAM (Fuel Shutoff Solenoid Energized to Shutoff)
1. Magnetic pickup. 2. Crank terminate switch. 3. Dual speed switch. 4. Time delay relay. 5. Switch (N.O.). 6. Shutdown relay. 7. Battery. 8. Diode assembly. 9. Shutoff solenoid. 10. Starter motor.

The engine speed is felt by magnetic pickup (1). As the teeth of the flywheel go through the magnetic lines of force around the pickup, an AC voltage is made. Dual speed switch (3) measures engine speed from the frequency of this AC voltage.

Time delay relay (4) controls the operation of shutdown relay (6), which in turn, controls the operation of fuel shutoff solenoid (9). Time delay relay (4) will keep the fuel shutoff solenoid energized for 70 seconds after a fault condition. This prevents the engine from being started again before the flywheel has stopped rotation.

When the engine starts and gets to a speed just above cranking speed, the normally open contacts of crank terminate switch (2) [which is part of dual speed switch (3)] will close. This will complete the circuit to time delay relay (4) through terminal TD-1. Normally open switch (5) in time delay relay (4) now closes and completes the circuit between shutdown relay (6) and terminal TD-7.

If the engine speed increases above the overspeed setting (118% of rated speed) of the dual speed switch, the overspeed switch (part of the dual speed switch) will close across terminals DSS-7 and DSS-8. This completes the circuit to shutdown relay (6) through the now closed switch (5) at terminal TD-7. Shutdown relay (6) is activated and in turn activates fuel shutoff solenoid (9) to cause the engine to shutdown.

When the engine stops, crank terminate switch (2) will open the circuit across terminals DSS-10 and DSS-11. This stops current flow to time delay relay (4). Now, the time delay relay timer is started and 70 seconds later, switch (5) will open the circuit at terminal TD-7. Current flow is then stopped through shutdown relay (6) and fuel shutoff solenoid (9) will no longer be activated.

A reset button on the dual speed switch must be pushed to open the overspeed switch before the engine will run.

Water Temperature And Oil Pressure Shutoff With Time Delay Relay (Fuel Shutoff Solenoid Energized To Run)

WIRING DIAGRAM
1. Time delay relay. 2. Water temperature switch. 3. Oil pressure switch. 4. Switch (N.C.). 5. Fuel shutoff solenoid.

When the electrical current is turned on to the time delay relay terminal four, the current will flow to oil pressure switch (3) and to terminal six of time delay relay (1). From terminal six the current flows through N.C. switch (4) to energize fuel shutoff solenoid (5) so the engine will start. When the engine starts, engine oil pressure will close the N.O. switch in oil pressure switch (3). This completes the circuit to time delay relay (1), water temperature switch (2) and fuel shutoff solenoid (5). N.C. switch (4) in the time delay relay now opens and breaks the circuit between fuel shutoff solenoid (5) and terminal six of the time delay relay.

If the engine coolant temperature goes above the setting of water temperature switch (2), the N.C. contacts will open. This stops current flow through water temperature switch (2) and through switch (4) to the fuel shutoff solenoid. When the engine stops, engine oil pressure will become less than the setting of the oil pressure switch. The N.O. switch will open and stop the flow of current to the time delay relay. This will start the time delay relay timer. After 70 seconds, switch (4) will close and current will again flow to the fuel shutoff solenoid.

If the oil pressure gets less than the setting of the oil pressure switch, the N.O. switch will open. This will stop current flow through switch (4) to the fuel shutoff solenoid. The current flow will stop to the time delay relay and start the time delay relay timer. After 70 seconds, switch (4) will close and current will again flow through the fuel shutoff solenoid.

NOTE: To help prevent discharge of the batteries when the engine is shut off, a switch can be installed to turn off the current to the shutoff solenoid.

WIRING SCHEMATIC (Water Temperature And Oil Pressure Shutoff)

BAT

Battery

CB

Circuit Breaker

OPS

Oil Pressure Switch

PS

Pinion Solenoid

SM

Starter Motor

SPB

Start Push Button

SS

Shutoff Solenoid

TDR

Time Delay Relay

VTS

Voltage Transient Suppressor

WTS

Water Temperature Switch

Water Temperature, Oil Pressure And Electronic Overspeed Shutoff With Time Delay Relay (Fuel Shutoff Solenoid Energized to Run)

WIRING DIAGRAM
1. Magnetic pickup. 2. Dual speed switch. 3. Overspeed switch (N.C.). 4. Cranking speed switch (N.O.). 5. Water temperature switch. 6. Oil pressure switch. 7. Time delay relay. 8. Switch (N.C.). 9. Fuel shutoff solenoid.

The engine speed is felt by magnetic pickup (1). As the teeth of the flywheel go through the magnetic lines of force around the pickup, an AC voltage is made. Dual speed switch (2) determines engine speed from the frequency of the voltage.

Time delay relay (7) controls the operation of fuel shutoff solenoid (9). To prevent the engine from restarting, the time delay relay turns off the current to the fuel shutoff solenoid for approximately 70 seconds after the engine stops.

When the electrical current is turned on to the time delay relay terminal four, the current then goes to terminals six and eleven of the dual speed switch and to terminal one of oil pressure switch (6). Current also flows to terminal six of the time delay relay and through N.C. switch (8) to energize fuel shutoff solenoid (9) so the engine will start.

When the engine starts, N.O. switch (4) in the cranking circuit of the dual speed switch closes at a speed just above cranking speed. This completes the circuit to terminal two of the time delay relay. In approximately 9 seconds N.C. switch (8) in the time delay relay will open and break the circuit between the fuel shutoff solenoid and terminal six of the time delay relay. If engine oil pressure has not closed oil pressure switch (6) by 9 seconds, N.C. switch (8) will open and break the circuit to fuel shutoff solenoid (9) causing engine shutdown. However, if engine oil pressure closes the N.O. switch in oil pressure switch (6), current will flow through water temperature switch (5), overspeed switch (3) and terminal five of time delay relay to the shutoff solenoid. Current also flows to terminal one of the time delay relay. This will immediately open N.C. switch (8).

If the speed of the engine gets more than the setting of the overspeed switch, N.C. switch (3) opens. This stops current flow to the fuel shutoff solenoid and will cause the engine to shutdown.

When the engine speed gets less than the cranking speed setting, switch (4) opens. This stops the flow of current to terminal two of the time delay relay. When the engine stops, engine oil pressure will become less than the setting of the oil pressure switch. The N.O. switch will open and stop the flow of current to terminal one of the time delay relay. This will start the time delay relay timer. After 70 seconds, switch (8) will close and again let current flow to the fuel shutoff solenoid.

After an overspeed shutdown, the overspeed switch must be reset.

When the engine has been started and is running, the time delay relay will open switch (8). If the engine coolant temperature goes above the setting of water temperature switch (5), the N.C. contacts will open. This stops current flow through the water temperature switch and through overspeed switch (3) to the fuel shutoff solenoid causing engine shutdown.

When the engine speeds gets less than the cranking speed setting, switch (4) opens. This stops the flow of current to terminal two of the time delay relay. When the engine stops, engine oil pressure will become less than the setting of the oil pressure switch. The N.O. switch will open and stop the flow of current to terminal one of the time delay relay. This will start the time delay relay timer. After 70 seconds, switch (8) will close and again let current flow to the fuel shutoff solenoid.

When the engine has been started and is running, the time delay relay will close switch (8). If the engine oil pressure gets less than the setting of oil pressure switch (6), the N.O. switch will open. This will stop current flow through switch (3) to the fuel shutoff solenoid causing engine shutdown. The current flow will also stop to terminal one of the time delay relay. When the engine speed gets less than the cranking speed setting, switch (4) opens. This stops the flow of current to terminal two of the time delay relay and starts the time delay relay timer. After 70 seconds, switch (8) will close and again let current flow to the fuel shutoff solenoid.

NOTE: To help prevent discharge of the batteries when the engine is shut off, a switch can be installed to turn off the current to the shutoff solenoid.

WIRING SCHEMATIC (Water Temperature, Oil Pressure And Overspeed Shutoff)

BAT

Battery

CB

Circuit Breaker

CT

Crank Terminate

D

Diode

DSS

Dual Speed Switch

MAG.PU

Magnetic Pickup

OPS

Oil Pressure Switch

OSS

Overspeed Switch

PS

Pinion Solenoid

SM

Starter Motor

SPB

Start Push Button

SS

Shutoff Solenoid

TDR

Time Delay Relay

VTS

Voltage Transient Suppressor

WTS

Water Temperature Switch

Alarm Contactor System

WIRING DIAGRAM
1. Oil pressure switch. 2. Water temperature contactor. 3. Source voltage. 4. Toggle switch (optional). 5. Alarm. 6. Signal lights.

If the oil pressure is too low or the water temperature is too high this system will activate alarm (5) and signal lights (6).

Before the engine is started it will be necessary to override oil pressure switch (1) or the alarm will activate. This is done by either a manual override button on the (earlier) oil pressure switch or toggle switch (4). Oil pressure will return the manual override button to the run position. The toggle switch must be manually closed when the engine has oil pressure.

WIRING DIAGRAM
1. Oil pressure switch. 2. Water temperature contactor. 3. Source voltage. 4. Toggle switch (optional). 6. Signal lights (three). 7. Air temperature contactor.

If the oil pressure is too low or the water temperature is too high this system will activate signal lights (6).

Before the engine is started it will be necessary to override oil pressure switch (1) or the signal lights will activate. This is done by either a manual override button on the (earlier) oil pressure switch or toggle switch (4). Oil pressure will return the manual override button to the run position. The toggle switch must be manually closed when the engine has oil pressure.

WIRING DIAGRAM
1. Oil pressure switch. 2. Water temperature contactor. 3. Source voltage. 4. Toggle switch (optional). 5. Alarm. 7. Air temperature contactor.

If the oil pressure is too low or the water temperature is too high this system will activate alarm (5).

Before the engine is started it will be necessary to override oil pressure switch (1) or the alarm will activate. This is done by either a manual override button on the (earlier) oil pressure switch or toggle switch (4). Oil pressure will return the manual override button to the run position. The toggle switch must be manually closed when the engine has oil pressure.

Water Temperature And Oil Pressure Shutoff System (With Oil Pressure Delay Or Fuel Pressure Switch)

WIRING DIAGRAM
1. Oil pressure switch. 2. Water temperature contactor. 3. Oil pressure (time delay) or fuel pressure switch. 4. Rack solenoid. 5. Diode assembly. 6. Starter. 7. Battery.

If the oil pressure is too low or the coolant temperature is too high this system will activate rack solenoid (4). The solenoid is connected to the fuel rack by linkage. When it is activated it will move to stop the flow of fuel to the engine. The engine will stop.

Before the engine can be started it will be necessary to push the manual override button on (earlier) oil pressure switch (1). Oil pressure will return the manual override button to the run position.

Diode assembly (5) is used to stop arcing, for protection of the system.

Oil pressure delay or fuel pressure switch (3) is used to prevent discharge of battery (7) through the solenoid when the engine is stopped.

Electronic Overspeed Shutoff System (With Oil Pressure Delay Or Fuel Pressure Switch)

WIRING DIAGRAM
1. Rack solenoid. 2. Oil pressure (time delay) or fuel pressure switch. 3. Dual speed switch. 4. Magnetic pickup. 5. Diode assembly. 6. Starter. 7. Battery.

The engine speed is felt by magnetic pickup (4). As the teeth of the flywheel go through the magnetic lines of force around the pickup, an AC voltage is made. Dual speed switch (3) measures engine speed from the frequency of this AC voltage.

Rack solenoid (2) is connected to the fuel rack by linkage. When it is activated, it will move to stop the flow of fuel to the engine.

If the engine speed increases above the overspeed setting (118% of rated speed) of the dual speed switch, the overspeed switch [which is part of dual speed switch (3)] will close across terminals DSS-7 and DSS-8. This completes the circuit to rack solenoid (1) through the now closed pressure switch (2) and activates the solenoid to shutdown the engine.

After an overspeed shutdown, a button on the dual speed switch must be pushed to open the overspeed switch before the engine will run.

Diode assembly (5) is used to stop arcing, for protection of the system.

An oil pressure (time delay) or fuel pressure switch (2) is used to prevent discharge of battery (7) through the solenoid when the engine is stopped. The dual speed switch can be connected to the battery constantly because it uses less than 20 MA of current when the engine is stopped.

Water Temperature, Oil Pressure And Electronic Overspeed Shutoff System (With Oil Pressure Delay Or Fuel Pressure Switch)

WIRING DIAGRAM
1. Oil pressure switch. 2. Oil pressure (time delay) or fuel pressure switch. 3. Water temperature contactor. 4. Dual speed switch. 5. Magnetic pickup. 6. Rack solenoid. 7. Diode assembly. 8. Starter motor. 9. Battery.

This system gives high water temperature, low oil pressure and overspeed protection to the engine.

Rack solenoid (6) is connected to the fuel rack by linkage. When it is activated it will move to stop the flow of fuel to the engine. The rack solenoid can be activated by oil pressure switch (1), water temperature contactor (3) or the overspeed switch that is part of dual speed switch (4).

If the oil pressure is too low or the coolant temperature is too high, oil pressure switch (1) or water temperature contactor (3) will close to complete the circuit and activate rack solenoid (6).

The engine speed is felt by magnetic pickup (5). As the teeth of the flywheel go through the magnetic lines of force around the pickup, an AC voltage is made. Dual speed switch (4) measures engine speed from the frequency of this AC voltage.

If the engine speed increases above the overspeed setting (118% of rated speed) of the dual speed switch, the overspeed switch [which is part of dual speed switch (4)] will close across terminals DSS-7 and DSS-8. This completes the circuit to rack solenoid (6) through pressure switch (2) and water temperature contactor (3) to activate the solenoid and shutdown the engine.

After an overspeed shutdown, a button on the dual speed switch must be pushed to open the overspeed switch before the engine will run.

Diode assembly (7) is used to stop arcing, for protection of the system.

An oil pressure (time delay) or fuel pressure switch (2) is used to prevent discharge of battery (9) through the solenoid when the engine is stopped. The dual speed switch can be connected to the battery constantly because it uses less than 20 MA of current when the engine is stopped.

NOTE: On systems that use an earlier type oil pressure switch, it will be necessary to push the manual override button before the engine can be started. Oil pressure will return the manual override button to the run position.

Mechanical Overspeed Shutoff System

WIRING SCHEMATIC (Typical Example)
1. Shutoff solenoid. 2. Diode assembly. 3. Oil pressure (time delay) or fuel pressure switch. 4. Overspeed switch. 5. Terminal block. 6. Starter. 7. Battery

The mechanical overspeed switch (4) is fastened to the tachometer drive on the engine. Wires connect the switch to the fuel shutoff solenoid. If the speed of the engine gets too high the overspeed switch sends a signal to activate shutoff solenoid (1).

The shutoff solenoid is connected to the fuel control shaft by linkage. When it is activated it will move to stop the flow of fuel to the engine.

After an overspeed shutdown the overspeed switch must be reset before the engine can start.

Diode assembly (2) is used to stop arcing, for protection of the system.

The optional grounds to the engine shown are used with grounded systems only.

An oil pressure (time delay) or fuel pressure switch (3) is used to prevent discharge of battery (7) through the solenoid when the engine is stopped.

Water Temperature, Oil Pressure And Mechanical Overspeed Shutoff System

WIRING SCHEMATIC (Typical Example)
1. Oil pressure switch (switch with manual override shown). 2. Water temperature contactor. 3. Oil pressure (time delay) or fuel pressure switch. 4. Overspeed switch. 5. Shutoff solenoid. 6. Diode assembly. 7. Terminal block. 8. Starter. 9. Battery.

The shutoff solenoid can be activated by oil pressure switch (1), water temperature contactor (2) or overspeed switch (4). See WATER TEMPERATURE AND OIL PRESSURE SHUTOFF SYSTEM and MECHANICAL OVERSPEED SHUTOFF SYSTEM.

Mechanical Oil Pressure And Water Temperature Shutoff

MECHANICAL SHUTOFF GROUP
1. Oil pressure sensing valve. 2. Tee. 3. Water temperature sensing valve. 4. Shutdown cylinder.

The shutdown cylinder (4) is mounted to the rear of the governor housing. The plunger of the cylinder acts on a spring-loaded lever assembly inside the governor housing. When extended, the plunger rotates the lever assembly to allow full movement of the fuel rack. When the plunger is retracted, the lever assembly returns to its original position which moves and holds the fuel rack in the shutoff position.

When starting the engine, the knob on shutdown cylinder (4) must be held in to extend the plunger against the lever assembly inside the governor housing. This will rotate the lever assembly to allow full rack movement. After the engine starts and oil pressure is high enough to hold the plunger extended, the knob can be released. Oil pressure will hold the plunger in this position until there is a low oil pressure condition.

Under normal operating conditions, pressure oil from the engine oil manifold flows to tee (2). Part of the oil from the tee flows through water temperature sensing valve (3) into the pressure inlet end of oil pressure sensing valve (1) where the oil flow is blocked and the oil pressure is monitored. The other part of the oil flow from tee (2) flows to and through the drain end of valve (2) on to shutdown cylinder (4) where the oil flow is blocked and the pressure holds the cylinder plunger extended.

When the oil pressure gets too low the drain end of valve (1) will open causing the pressure oil to cylinder (4) to drain back to the engine block. With no oil pressure in cylinder (4), the lever assembly in the governor returns to its original position pushing the cylinder plunger to the retracted position and moves the fuel rack to the shutoff position to stop the engine.

When the water temperature is too high, the pressure oil that flows through water temperature sensing valve (3) is diverted to drain within the valve body and flows back to the engine block. This causes the oil pressure to become too low and the engine will stop as described above.

Shutoff And Alarm System Components

Oil Pressure Switch

Micro Switch Type

The oil pressure switch is used to give protection to the engine from damage because of low oil pressure. When oil pressure lowers to the pressure specifications of the switch, the switch closes and activates the rack shutoff solenoid.

On automatic start/stop installations, this switch closes to remove the starting system from the circuit when the engine is running with normal oil pressure.

This switch for oil pressure can be connected in a warning system for indication of low oil pressure with a light or horn.

As pressure of the oil in bellows (6) becomes higher, arm (4) is moved against the force of spring (3). When projection (10) of arm (4) makes contact with arm (9), pressure in the bellows moves both arms. This also moves button (8) of the micro switch to activate the micro switch.

OIL PRESSURE SWITCH (Micro Switch Type)
1. Locknut. 2. Adjustment screw. 3. Spring. 4. Arm. 5. Spring. 6. Bellows. 7. Latch plate. 8. Button for micro switch. 9. Arm. 10. Projection of arm.

Some of these switches have a "Set For Start" button. When the button is pushed in, the micro switch is in the START position. This is done because latch plate (7) holds arm (9) against button (8) of the micro switch and the switch operates as if the oil pressure was normal. When the engine is started, pressure oil flows into bellows (6). The bellows move arm (4) into contact with latch plate (7). The latch plate releases the "Set For Start" button and spring (5) moves it to the RUN Position. This puts the switch in a ready to operate condition.

Pressure Switch

Pressure switches are used for several purposes and are available with different specifications. They are used in the oil system and in the fuel system. One use of the switch is to open the circuit between the battery and the rack shutoff solenoid after the oil pressure is below the pressure specifications of the switch. It also closes when the engine starts.

Another use of the switch is to close and activate the battery charging circuit when the pressure is above the pressure specification of the switch. It also disconnects the circuit when the engine is stopped.

Switches of this type have three terminal connections. They are used to do two operations with one switch. They open one circuit and close another with the single switch.

Shutoff Solenoid

A shutoff solenoid changes electrical input into mechanical output. It is used to move the fuel injection pump rack to the off position.

The shutoff solenoid can be activated by any one of the many sources. The most usual are: water temperature contactor, oil pressure switch, overspeed switch and remote manual control switch.

RACK SHUTOFF SOLENOID (Typical Illustration)

Water Temperature Contactor Switch

The contactor switch for water temperature is installed in the water manifold. No adjustment to the temperature range of the contactor can be made. The element feels the temperature of the coolant and then operates the micro switch in the contact when the coolant temperature is too high, the element must be in contact with the coolant to operate correctly. If the cause for the engine being too hot is because of low coolant level or no coolant, the contactor switch will not operate.

The contactor switch is connected to the rack shutoff solenoid to stop the engine. The switch can also be connected to an alarm system. When the temperature of the coolant lowers to the operating range, the contactor switch opens automatically.

WATER TEMPERATURE CONTACTOR SWITCH

Circuit Breaker

The circuit breaker gives protection to an electrical circuit. Circuit breakers are rated as to how much current they will permit to flow. If the current in a circuit gets too high it will cause heat in disc (3). Heat will cause distortion of the disc and contacts (2) will open. No current will flow in the circuit.

CIRCUIT BREAKER SCHEMATIC
1. Disc in open position. 2. Contacts. 3. Disc. 4. Circuit terminals.

An open circuit breaker will close (reset) automatically when it becomes cooler.

Mechanical Overspeed Switch

The overspeed switch is installed on the tachometer drive shaft on the fuel injection pump. The switch activates when the engine speed is equal to the overspeed setting. When the overspeed switch has activated, the contacts do not automatically return to their normal positions. The reset button (1) must be pushed by the operator to make the switch contacts return to their normal positions. The usual setting for the overspeed switch is 18% higher than the rated speed of the engine.

MECHANICAL OVERSPEED SWITCH
1. Button.

Some overspeed switches also have underspeed contacts. These contacts close at approximately 600 rpm as the engine speed increases. The underspeed setting is not adjustable.

Electronic Speed Switch

The electronic speed switch (dual speed switch) activates the shutoff solenoid when the engine speed gets approximately 18% higher than the rated full load speed of the engine. It also stops current flow to the starter motor after the engine starts.

MAGNETIC PICKUP INSTALLED

The electronic speed switch makes a comparison between the output frequency of the magnetic pickup and the setting of the electronic speed switch. When they are equal, the normally open contacts in the electronic speed switch close. Lamp (2) will go on. The switch also has a failsafe circuit that will cause the engine to shutdown if there is an open in the magnetic pickup circuit.

When the engine is stopped, it will be necessary to push reset button (1), before the engine can be started.

ELECTRONIC SPEED SWITCH
1. Reset button. 2. Lamp.