Hydramechanical Protective System

The hydramechanical protective system is designed as a self contained system separate from the engine governor. This system is used to activate an alarm or shutdown an engine for low oil pressure, high coolant temperature or engine overspeed conditions.

Overspeed

In general, an overspeed condition is the result of a fuel system that fails to operate correctly. This in turn allows the combustion system to get more fuel than the engine load needs. The excess fuel can accelerate the engine to a point that engine failure can be the result.

The rate of engine acceleration is controlled by several factors. Friction horsepower, attached inertial loads and operating loads make up the main affects on acceleration. In most all cases, the protective system must have a response time of less than one second. Response time is the time interval between the overspeed and the actuation of the protective system. The protective system must provide this response under different conditions such as engine start up at extreme ambient temperatures and under full load operation.

For an overspeed condition the fuel control linkage is moved to the "SHUTOFF" position and the engine combustion air supply is stopped.

Low Engine Oil Pressure

As engine speed increases, the required oil pressure for main bearing protection increases. The engine oil pump is a positive displacement type pump, therefore, engine oil pressure varies in direct proportion to speed until the pump goes on controlled bypass.

From Figure 1, it can be seen that if only the low range oil pressure protection level was used for the full speed range, the engine could operate at rated speed with oil pressure below the required level. Also, if only the high range oil pressure protection level was used for the full speed range, the system would shutdown the engine at low idle, since the engine oil pump develops lower pressure at that speed. Therefore, the protective system must operate between the required oil pressure curve and the engine oil pressure curve. This is done with a step action of pressure versus speed.

The hydramechanical protective system operates within the two ranges of engine oil pressure. As engine speed increases, the minimum oil pressure needed at the main bearings also increases. At low engine speed, an alarm or fuel shutoff actuator will activate when oil pressure is reduced to within 140 ± 35 kPa (20 ± 5 psi). At high engine speeds, an alarm or fuel shutoff actuator will activate when oil pressure is reduced to within 205 ± 35 kPa (30 ± 5 psi).

For a low oil pressure condition, the protective system activates an alarm or moves the fuel control linkage, through the governor, to the "SHUTOFF" position. The combustion air supply is not shutoff for this condition.

High Coolant Temperature

If the coolant temperature of an engine goes above a set limit, the protective system activates an alarm or moves the fuel control linkage to the "SHUTOFF" position to shutdown the engine. The combustion air supply is not stopped under this condition.

System Components

The system consists of an emergency manual shutoff, a shutoff control group, a diverter valve, a thermostatic pilot valve, an air inlet shutoff and a fuel shutoff actuator for the governor.

The air and fuel shutoff systems are separate from each other to give complete engine shutdown for an overspeed condition. If the engine fuel is held in the "ON" position, the air inlet shutoff must work to shutdown the engine.

Emergency Manual Shutoff

This shutoff is used under emergency conditions to shutdown the engine manually. When operated, this shutoff simulates an engine overspeed condition in the protective system. Thus, the air and fuel to the combustion chambers is stopped. The shutoff is also used to check the protective system for correct operation at regular engine maintenance periods.

The emergency manual shutoff can be operated at the engine or from a remote location. For remote operation, either air or electric power can be used.

Shutoff Control Group

SHUTOFF CONTROL GROUP
1. Spring for overspeed adjustment. 2. Emergency manual shutoff valve. 3. Valve spool (not used). 4. Selector valve. 5. Speed sensing valve spool. 6. Speeder spring. 7. Flyweights. 8. Low speed oil protection valve. 9. High speed oil protection valve. 10. Oil pump. 11. Oil pressure relief valve. 12. Pressure control valve group which consists of: the fuel and air inlet sequence valves, the two-way pilot operated valve and emergency manual shutoff valve (2).

A flyweight controlled, speed sensing valve spool is used to feel engine speed. The speed sensing valve spool is moved by flyweights which are turned by a drive shaft. The drive shaft is driven by the engine camshaft through an accessory drive group that has an oil reservoir for the shutoff system. When engine speed increases, the flyweights move out and push the speed sensing valve spool out to open and close passages to put oil pressure into the correct system circuits. This gives correct protective system operation under the two engine oil pressure ranges.

Diverter Valve

If there is a low oil pressure, high coolant temperature or engine overspeed condition, the diverter valve moves to put system oil pressure in the fuel shutoff circuit. This moves the governor and fuel control linkage to the "SHUTOFF" position to shutdown the engine.

Thermostatic Pilot Valve

This valve is used to feel engine coolant temperature. If the coolant temperature goes above the limit of the thermostatic pilot valve, the valve opens and causes engine shutdown through the fuel shutoff circuit of the protective system.

Water Temperature Contactor

The contactor switch for water temperature is installed in the water manifold housing (below the regulator housing). This is normally where the thermostatic pilot valve is installed. No adjustment to the temperature range of the contactor can be made. The element feels the temperature of the coolant and then operates a micro switch (in the contactor) when the coolant temperature is too high. The element must be in contact with the coolant to operate correctly. If the cuase for the engine being too hot is because of low coolant level or no coolant, the contactor switch will not operate.

The switch is connected to an alarm system and activates an alarm under high coolant temperature conditions. When the temperature of the coolant lowers to the operating range, the contactor switch opens automatically.

WATER TEMPERATURE CONTACTOR SWITCH

Air Inlet Shutoff

The air inlet shutoff consists of a shutoff valve in the engine air inlet housing and a hydraulic actuator that holds the shutoff valve in the "OPEN" position.

If an engine is operated in a combustible atmosphere, such as an oil or gas blow out on an oil rig, the air supply must be stopped to give a positive method of engine shutdown. If only the fuel control linkage was moved to the "SHUTOFF" position, the engine may continue to run on the air-oil-gas mixture pulled into the engine air intake.

The hydramechanical protective system closes the air inlet shutoff valve to stop combustion air supply to the engine in an overspeed condition, to give a more positive shutdown. The air inlet shutoff valve is also closed when the emergency manual shutoff is operated.

Since overspeed is a serious occurrence, the air inlet shutoff must be manually reset. This action requires a person to physically go to the engine and see if any damage has occurred.

Fuel Shutoff Actuator

This actuator is located on top of the Woodward UG-8 or the Caterpillar 3161 Governor. The actuator can be either an electric or hydraulic actuator that is operated any time the hydramechanical protective system causes engine shutdown.

When operated by the diverter valve, the actuator moves the governor shutoff strap which causes the governor to move the engine fuel control linkage to the "SHUTOFF" position.

Component Locations On Engine

SHUTOFF CONTROL GROUP
1. Oil lines to air inlet shutoff actuator. 2. Rack sequence valve. 3. Shutoff control group. 4. Engine oil pressure line. 5. Emergency manual shutoff valve. 6. Cover (oil reservoir). 7. Diverter valve. 8. Air inlet sequence valve.

SHUTOFF CONTROL GROUP
3. Shutoff control group. 4. Engine oil pressure line. 7. Diverter valve. 9. Oil line to thermostatic pilot valve. 10. Oil line to fuel shutoff actuator.

AIR INLET SHUTOFF
11. Air inlet shutoff housing. 12. Air inlet shutoff actuator. 13. Aftercooler housing.

AIR INLET SHUTOFF
11. Air inlet shutoff housing. 13. Aftercooler housing. 14. Reset knob.

COOLANT TEMPERATURE PROTECTION
13. Aftercooler housing (coolant inlet). 15. Thermostatic pilot valve. 16. Housing (below regulator housing).

GOVERNOR SHUTOFF ACTUATOR (Woodward UG-8 Governor Shown)
9. Oil line to thermostatic pilot valve. 10. Oil line to fuel shutoff actuator. 17. Fuel shutoff actuator.

System Hydraulics

Engine lubrication oil (under pressure) is sent to the oil reservoir for the shutoff control. The reservoir keeps the correct level of oil for the system and drains the excess oil back into the engine. This gives a constant oil supply to the system.

An oil pump and pressure relief valve (located in the shutoff control group) supplies oil flow and pressure for the protective system hydraulic circuits.

There are two main hydraulic circuits in the protective system. One circuit is for the fuel shutoff and the other is for air inlet shutoff. A constant flow of oil through the air inlet shutoff circuit removes (bleeds) air and keeps the lines full of oil to give a minimum time for system response. If a fault condition occurs, the oil pressure in one or both hydraulic circuits is increased to operate an actuator to shutdown an engine or activate an alarm.

Hydraulic Circuits (Earlier) - (Without Check Valves In Diverter Valve)

The schematics that follow, show only hydraulic actuators that are filled to cause engine shutdown. The fuel shutoff actuator can be replaced with an electric solenoid that is operated by the system hydraulics with the use of a pressure switch.

NOTE: Some of the schematics show only the components needed for explanation and do not show the complete hydramechanical protective system circuits.

SCHEMATIC NO. 1 (COMPLETE HYDRAMECHANICAL PROTECTIVE SYSTEM)
1. Selector valve. 2. Low speed oil protection valve. 3. Start-up override valve. 4. Diverter valve orifice. 5. Engine oil pressure orifice. 6. Speed sensing valve spool. 7. Diverter valve. 8. Fuel shutoff actuator. 9. Thermostatic pilot valve. 10. High speed oil protection valve. 11. Emergency manual shutoff valve. 12. Air inlet shutoff actuator. 13. Air inlet sequence valve. 14. Pilot operated two-way valve. 15. Fuel shutoff sequence valve. 16. Air inlet shutoff valve. 17. Oil pump. 18. Oil pressure relief valve.

Low Speed Range (Normal Engine Oil Pressure)

SCHEMATIC NO. 2 (LOW ENGINE OIL PRESSURE CIRCUIT) (Low Speed Range)
1. Selector valve. 2. Low speed oil protection valve. 4. Diverter valve orifice. 6. Speed sensing valve spool. 7. Diverter valve. 8. Fuel shutoff actuator. 10. High speed oil protection valve. 15. Fuel shutoff sequence valve. 17. Oil pump.

Make Reference to Schematic No. 2

When an engine is started and speed increases, engine oil pressure moves low speed oil protection valve (2) open. At the same time, oil in the protective system flows from oil pump (17) to fuel shutoff sequence valve (15) and diverter valve (7). Fuel shutoff sequence valve (15) keeps the inlet pressure to diverter valve (7) at 760 kPa (110 psi) and then directs the remainder of oil flow through the air inlet shutoff circuit. Most of the air inlet shutoff circuit has been left out since it is not directly in use at this point.

At diverter valve (7), the oil flows through orifice (4) which causes a pressure difference across both ends of the valve spool. The valve spool is then moved by system oil pressure, against a spring force, to keep the fuel shutoff actuator from being operated. The oil then flows from diverter valve (7) to drain through low speed oil protection valve (2) and selector valve (1).

NOTE: Engine oil pressure is not high enough at this point to move valve (10) against the force of the spring.

Low Speed Range (Low Engine Oil Pressure Fault)

SCHEMATIC NO. 3 (LOW ENGINE OIL PRESSURE FAULT) (Low Speed Range)
1. Selector valve. 2. Low speed oil protection valve. 4. Diverter valve orifice. 6. Speed sensing valve spool. 7. Diverter valve. 8. Fuel shutoff actuator. 10. High speed oil protection valve. 15. Fuel shutoff sequence valve. 17. Oil pump.

Make Reference to Schematic No. 3

If the engine oil pressure goes below 105 kPa (15 psi), the spring force on low speed oil protection valve (2) will close the valve. The oil flow in the circuit is then stopped and can not flow to drain. The pressure of the oil will become equal on both sides of diverter valve orifice (4). Spring force will move the valve spool of diverter valve (7) down so that there is alignment with the passage that leads to fuel shutoff actuator (8). Oil pressure will now activate the fuel shutoff actuator, which will cause the governor to move the fuel control linkage to the "SHUTOFF" position and shutdown the engine.

High Speed Range (Normal Engine Oil Pressure)

SCHEMATIC NO. 4 (LOW ENGINE OIL PRESSURE CIRCUIT) (High Speed Range)
1. Selector valve. 2. Low speed oil protection valve. 4. Diverter valve orifice. 6. Speed sensing valve spool. 7. Diverter valve. 8. Fuel shutoff actuator. 10. High speed oil protection valve. 12. Air inlet shutoff actuator. 13. Air inlet sequence valve. 14. Pilot operated two-way valve. 15. Fuel shutoff sequence valve. 16. Air inlet shutoff valve. 17. Oil pump. 18. Oil pressure relief valve.

Make Reference to Schematic No. 4

At approximately 70% of engine full load speed, the oil pressure protection changes from the low speed range to the high speed range. At this point engine oil pressure is high enough to open high speed oil protection valve (10).

System oil flow to diverter valve (7) is the same as it is for the low speed range except speed sensing valve spool (6) has been shifted. When the engine speed increases to the high speed range, speed sensing valve spool (6) will be moved up by the flyweights. This directs system oil pressure at 760 kPa (110 psi) to selector valve (1). The valve closes to remove low range oil pressure protection valve (2) from the circuit. The oil now flows from diverter valve (7) to drain through high speed oil protection valve (10) and pilot operated two-way valve (14).

High Speed Range (Low Engine Oil Pressure Fault)

SCHEMATIC NO. 5 (LOW ENGINE OIL PRESSURE FAULT) (High Speed Range)
1. Selector valve. 2. Low speed oil protection valve. 4. Diverter valve orifice. 6. Speed sensing valve spool. 7. Diverter valve. 8. Fuel shutoff actuator. 10. High speed oil protection valve. 15. Fuel shutoff sequence valve. 17. Oil pump.

Make Reference to Schematic No. 5

When engine oil pressure decreases to 175 kPa (25 psi), the spring force on high speed oil protection valve (10) will move the valve to stop oil flow to the drain. The difference in oil pressure across diverter valve orifice (4) will now go to zero. The valve spool of diverter valve (7) will move down by spring force, which will cause alignment of the ports to fuel shutoff actuator (8). The actuator now causes the governor to move the fuel control linkage to the "SHUTOFF" position and shutdown the engine.

High Engine Coolant Temperature Circuit (Normal Conditions)

SCHEMATIC NO. 6 (ENGINE COOLANT TEMPERATURE CIRCUIT) (Low Speed Range Shown)
1. Selector valve. 2. Low speed oil protection valve. 4. Diverter valve orifice. 7. Diverter valve. 8. Fuel shutoff actuator. 9. Thermostatic pilot valve. 10. High speed oil protection valve. 15. Fuel shutoff sequence valve.

Make Reference to Schematic No. 6

Under high coolant temperature conditions, the low engine oil pressure circuits are used to shutdown an engine. The schematic shows the low speed range engine oil pressure circuit in use and the coolant temperature circuit added to the engine oil pressure line. Engine temperature is normal and thermostatic pilot valve (9) is closed.

Oil flow through the system is the same as in the low and high speed range of the LOW ENGINE OIL PRESSURE CIRCUIT.

NOTE: The sensor of the thermostatic pilot valve (9) must be below the water level in the coolant manifold to operate.

High Engine Coolant Temperature Circuit (Fault Condition)

SCHEMATIC NO. 7 (HIGH ENGINE COOLANT TEMPERATURE FAULT)
1. Selector valve. 2. Low speed oil protection valve. 4. Diverter valve orifice. 7. Diverter valve. 8. Fuel shutoff actuator. 9. Thermostatic pilot valve. 10. High speed oil protection valve. 15. Fuel shutoff sequence valve.

Make Reference to Schematic No. 7

When engine coolant temperature increases to 99°C (210°F), thermostatic pilot valve (9) will open. This will let engine oil in the circuit drain and cause a decrease in oil pressure on low speed oil protection valve (2) and high speed oil protection valve (10). Valves (2) and (10) will close and stop oil flow from diverter valve (7). The difference in oil pressure across diverter valve orifice (4) will now go to zero. The valve spool of diverter valve (7) will move down by spring force, which will cause alignment of the ports to fuel shutoff actuator (8). The actuator now causes the governor to move the fuel control linkage to the "SHUTOFF" position and shutdown the engine.

Overspeed Circuit (Normal Conditions)

SCHEMATIC NO. 8 (OVERSPEED CIRCUIT)
1. Selector valve. 2. Low speed oil protection valve. 3. Start-up override valve. 4. Diverter valve orifice. 5. Engine oil pressure orifice. 6. Speed sensing valve spool. 7. Diverter valve. 8. Fuel shutoff actuator. 9. Thermostatic pilot valve. 10. High speed oil protection valve. 11. Emergency manual shutoff valve. 12. Air inlet shutoff actuator. 13. Air inlet sequence valve. 14. Pilot operated two-way valve. 15. Fuel shutoff sequence valve. 16. Air inlet shutoff valve. 17. Oil pump. 18. Oil pressure relief valve.

Make Reference to Schematic No. 8

When an engine is started and speed increases, engine oil pressure opens low speed oil protection valve (2) and high speed oil protection valve (10). At the same time, oil in the protective system flows from oil pump (17) to fuel shutoff sequence valve (15), speed sensing valve spool (6) and diverter valve (7). Fuel shutoff sequence valve (15) keeps the oil pressure to diverter valve (7) and speed sensing valve spool (6) at 760 kPa (110 psi) and then directs the remainder of oil flow through the air inlet shutoff circuit. At higher engine speeds, speed sensing valve spool (6) directs oil pressure to close selector valve (1).

Oil in the air inlet shutoff circuit is directed to air inlet sequence valve (13) and air inlet shutoff actuator (12). Air inlet sequence valve (13) keeps the oil pressure in air inlet shutoff actuator (12) at 105 kPa (15 psi) and then directs the remainder of oil flow to drain through pilot operated two-way valve (14), which is normally open. Pilot operated two-way valve (14) is held open by spring force and the pilot oil pressure is connected to the drain through speed sensing valve spool (6).

At diverter valve (7), the oil flows through orifice (4) which causes a pressure difference across both ends of the valve spool. The valve spool is then moved by system oil pressure, against a spring force, to keep the fuel shutoff actuator from being operated. The oil then flows from diverter valve (7) to drain through high speed oil protection valve (10) and pilot operated two-way valve (14).

NOTE: Low engine oil pressure or high coolant temperature conditions do not change the oil flow in the air inlet shutoff circuit.

Overspeed Circuit (Overspeed Fault)

SCHEMATIC NO. 9 (OVERSPEED FAULT)
1. Selector valve. 2. Low speed oil protection valve. 4. Diverter valve orifice. 6. Speed sensing valve spool. 7. Diverter valve. 8. Fuel shutoff actuator. 12. Air inlet shutoff actuator. 13. Air inlet sequence valve. 14. Pilot operated two-way valve. 15. Fuel shutoff sequence valve. 18. Oil pressure relief valve.

Make Reference to Schematic No. 9.

When the engine speed is 18% above full load speed, speed sensing valve spool (6) will be moved up by the flyweights. This will send oil to pilot operated two-way valve (14) and to the spring side of air inlet sequence valve (13). The oil pressure will close both valves and oil in the air inlet shutoff system can not go to drain. The oil pressure in the system will increase until oil pressure relief valve (18) opens at 1720 kPa (250 psi). The increased pressure will move air inlet shutoff actuator (12), which will release the air inlet shutoff valve. This stops the combustion air supply to the engine. Fuel shutoff circuit oil also can not go to drain. The difference in oil pressure across diverter valve orifice (4) will now go to zero. The valve spool of diverter valve (7) will move down by spring force, which will cause alignment of the ports to fuel shutoff actuator (8). Now, oil pressure in the fuel shutoff circuit will activate fuel shutoff actuator (8), which will cause the governor to move the fuel control linkage to the "SHUTOFF" position.

NOTE: Because the air inlet shutoff is the most positive way to shutdown an engine, air inlet shutoff actuator (12) is activated by the protective system before fuel shutoff actuator (8) is activated.

Emergency Manual Shutoff

SCHEMATIC NO. 10 (EMERGENCY MANUAL SHUTOFF)
4. Diverter valve orifice. 6. Speed sensing valve spool. 7. Diverter valve. 8. Fuel shutoff actuator. 11. Emergency manual shutoff valve. 13. Air inlet sequence valve. 14. Pilot operated two-way valve. 15. Fuel shutoff sequence valve. 18. Oil pressure relief valve.

Make Reference to Schematic No. 10

When the knob on emergency manual shutoff (11) is pulled, system oil flow is directed to pilot operated two-way valve (14) to close the valve. This stops oil flow to drain in both the fuel and air inlet shutoff circuits. The protective system then, shuts down the engine in the same sequence as for an overspeed fault condition. The combution air supply is stopped and the fuel control linkage is moved to the "SHUTOFF" position to shutdown the engine.

Start-Up Override Of Low Engine Oil Pressure

SCHEMATIC NO. 11 (START-UP OVERRIDE)
2. Low speed oil protection valve. 3. Start-up override valve. 4. Diverter valve orifice. 7. Diverter valve. 8. Fuel shutoff actuator. 15. Fuel shutoff sequence valve.

Make Refeence to Schematic No. 11

On a hot restart, after severe operating conditions, the engine oil pressure can increase slowly. If the rate of pressure increase is too slow, the protective system activates fuel shutoff actuator (8) to move the fuel control linkage to the "SHUTOFF" position because of a low engine oil pressure fault condition. Therefore, an override of the engine oil pressure circuit is needed in the protective system.

An electric solenoid or air operated start-up override valve (3) is installed in the diverter valve return line. The valve is normally closed. When start-up override valve (3) is operated, the outlet of the diverter valve is connected to drain. This maintains a pressure drop across diverter valve orifice (4) and does not let the diverter valve shift to the shutdown position.

When start-up override valve (3) is not in use, the engine oil circuit is put back into normal operation as in Schematics No. 2 and No. 4.

Remote Normal Shutoff

SCHEMATIC NO. 12 (REMOTE NORMAL SHUTOFF)
4. Diverter valve orifice. 7. Diverter valve. 8. Fuel shutoff actuator. 19. Remote normal shutoff valve.

Make Reference to Schematic No. 12

The remote normal shutoff is an option that can be used with the hydramechanical protective system. An air or electric operated remote normal shutoff valve (19) is installed in the diverter valve return line. When remote normal shutoff valve (19) is operated, the outlet of the diverter valve is stopped. The oil pressure becomes equal on both sides of diverter valve orifice (4). Spring force will move the valve spool of diverter valve (7) to make an alignment of the oil passage with the oil line to fuel shutoff actuator (8). Oil pressure can now activate fuel shutoff actuator (8) which causes the governor to move the fuel control linkage to the "SHUTOFF" position and shutdown the engine.

Hydraulic Circuits (Later) (With Check Valves in Diverter Valve)

Later hydramechanical protective systems have hydraulic circuits that use check valves to hold hydraulic pressure on (lock) the fuel shutoff actuator in the "SHUTOFF" position, after the engine has been shutdown. In this system, the start-up override valve must be operated to release the hydraulic pressure from the fuel shutoff actuator before the engine can be started. Also, make sure the air inlet shutoff is in the open position before the engine is started.

The operation of these hydraulic circuits is the same as that of the earlier hydraulic circuits except for the check valves in the diverter valve for the fuel shutoff circuit.

Start-Up Override

SCHEMATIC NO. 13 (START-UP OVERRIDE)
1. Selector valve. 2. Low speed oil protection valve. 3. Start-up override valve. 4. Diverter valve orifice. 7. Diverter valve. 8. Fuel shutoff actuator. 10. High speed oil protection valve. 15. Fuel shutoff sequence valve. 17. Oil pump. 19. Remote normal shutoff valve.

Make Reference to Schematic No. 13

When operated, the start-up override valve connects the fuel shutoff actuator circuit to drain. This removes any hydraulic pressure on the actuator so the governor can move the fuel control linkage and the engine can be started.

Also, on hot restart, after severe operating conditions, the engine oil pressure can increase slowly. If the rate of pressure increase is too slow, the protective system activates actuator (8) to move the fuel control linkage to the "SHUTOFF" position because of a low engine oil pressure fault. Therefore, an override of the low engine oil pressure circuit is needed in the protective system.

An electric solenoid or air operated start-up override valve (3) is installed in the diverter valve return line. The valve is normally closed. When start-up override valve (3) is operated, the outlet of the diverter valve is connected to drain. This maintains a pressure drop across orifice (4) and does not let the diverter valve shift to the shutdown position. The fuel shutoff actuator line is also connected to drain to make sure fuel shutoff actuator (8) does not hold the governor shutoff strap in the off position.

When start-up override valve (3) is not in use, the engine oil circuit is put back into normal operation as in Schematics No. 2 and No. 4.

Low Speed Range (Low Engine Oil Pressure Fault)

SCHEMATIC NO. 14 (LOW ENGINE OIL PRESSURE FAULT) (Low Speed Range)
1. Selector valve. 2. Low speed oil protection valve. 3. Start-up override valve. 4. Diverter valve orifice. 6. Speed sensing valve spool. 7. Diverter valve. 8. Fuel shutoff actuator. 10. High speed oil protection valve. 15. Fuel shutoff sequence valve. 17. Oil pump. 19. Remote normal shutoff valve.

Make Reference to Schematic No. 14

If the engine oil pressure goes below 140 kPa (20 psi), the spring force on low speed oil protection valve (2) will close the valve. The oil flow in the circuit is then stopped and can not flow to drain. The pressure of the oil will become equal on both sides of diverter valve orifice (4). Spring force will move the valve spool of diverter valve (7) down so that there is alignment with the passage that leads to fuel shutoff actuator (8). Oil pressure will now move the fuel shutoff actuator which will cause the governor to move the fuel control linkage to the "SHUTOFF" position and shutdown the engine.

As the crankshaft rpm becomes slower, the governor feels the speed reduction and moves the terminal shaft and linkage in the fuel "ON" direction, against fuel shutoff actuator (8). This moves the protective system oil back toward the system oil pump. The check valves in diverter valve (7) move to stop this oil flow and keep the engine from surging.

NOTE: The start-up override valve (3) must be operated to release the fuel shutoff actuator hydraulic pressure before the engine can be started.

Remote Normal Shutoff

SCHEMATIC NO. 15 (REMOTE NORMAL SHUTOFF)
3. Start-up override. 4. Diverter valve orifice. 7. Diverter valve. 8. Fuel shutoff actuator. 19. Remote normal shutoff valve.

Make Reference to Schematic No. 15

The remote normal shutoff is an option that can be used with the hydramecahnical protective system. An air or electric operated remote normal shutoff valve (19) is installed in the diverter valve return line. When remote normal shutoff valve (19) is operated, the outlet of the diverter valve is stopped. The oil pressure becomes equal on both sides of diverter valve orifice (4). Spring force will move the valve spool of diverter valve (7) to make an alignment of the oil passage with the oil line to fuel shutoff actuator (8). Oil pressure can now activate the fuel shutoff actuator, which causes the governor to move the fuel control linkage to the "SHUTOFF" position and shutdown the engine.

As the crankshaft rpm becomes slower, the governor feels the speed reduction and moves the terminal shaft and linkage in the fuel "ON" direction, against fuel shutoff actuator (8). This moves the protective system oil back toward the system oil pump. The check valves in diverter valve (7) move to stop this oil flow and keep the engine from surging.

NOTE: The start-up override valve (3) must be operated to release the fuel shutoff actuator hydraulic pressure before the engine can be started.

Later Hydraulic Circuits With An Alarm System

This hydramechanical protective system is designed to give automatic engine shutdown from an overspeed condition only. An alarm is activated for low engine oil pressure and high coolant temperature conditions.

The main difference between this system and systems shown in the EARLIER and LATER HYDRAULIC CIRCUITS, is that the fuel shutoff circuit oil return from the diverter valve is connected with the air inlet shutoff circuit return, and not to the normal fuel shutoff return port on the shutoff control group. A normally open pressure switch (13) is installed in the shutoff control group at the location the diverter valve oil return line is normally connected. Also, there is an orifice plug [orifice (14)] installed in the shutoff control group. The orifice plug is located in the valve body that holds valves (4), (8) and (9). In the hydraulic circuit, this orifice is between the oil pressure supply and the low and high oil pressure protection valves (8) and (9).

SHUTOFF CONTROL GROUP
1. Spring for overspeed adjustment. 2. Emergency manual shutoff valve. 3. Selector valve. 4. Valve spool (not used). 5. Speed sensing valve spool. 6. Speeder spring. 7. Flyweights. 8. Low speed oil protection valve. 9. High speed oil protection valve. 10. Oil pump. 11. Oil pressure relief valve. 12. Pressure control valve group which consists of: the fuel and air inlet sequence valves, the two-way pilot operated valve and emergency manual shutoff valve (2).

Overspeed Circuit (Normal Conditions)

SCHEMATIC NO. 16 (OVERSPEED CIRCUIT)
2. Emergency manual shutoff valve. 3. Selector valve. 5. Speed sensing valve spool. 8. Low speed oil protection valve. 9. High speed oil protection valve. 10. Oil pump. 11. Oil pressure relief valve. 13. Oil pressure switch. 14. Orifice. 15. Diverter valve orifice. 16. Remote normal shutoff valve. 17. Fuel shutoff actuator. 18. Diverter valve. 19. Engine oil pressure orifice. 20. Start-up override valve. 21. Thermostatic pilot valve. 22. Air inlet sequence valve. 23. Pilot operated two-way valve. 24. Fuel shutoff sequence valve. 25. Air inlet shutoff. 26. Air inlet shutoff actuator.

Make Reference to Schematic No. 16

When an engine is started and speed increases, engine oil pressure opens low speed oil protection valve (8) and high speed oil pressure protection valve (9). At the same time, oil in the protective system flows from oil pump (10) to fuel shutoff sequence valve (24) and is divided between the fuel shutoff and air inlet shutoff circuits. Fuel shutoff sequence valve (24) keeps the oil pressure at the start of the fuel shutoff circuit at 760 kPa (110 psi).

Oil in the air inlet shutoff circuit is directed to air inlet sequence valve (22) and air inlet shutoff actuator (26). Air inlet sequence valve (22) keeps the oil pressure in air inlet shutoff actuator (26) at 105 kPa (15 psi) and then directs the remainder of oil flow to drain through pilot operated two-way valve (23) which is normally open. Pilot operated two-way valve (23) is held open by spring force and the pilot oil pressure is connected to drain through speed sensing valve spool (5).

Oil flow in the fuel shutoff circuit is divided into different directions as follows:

1. Oil from fuel shutoff sequence valve (24) goes to speed sensing valve spool (5) and is stopped at low engine speeds. When engine speed is high enough, speed sensing valve spool (5) moves to direct the oil pressure and close selector valve (3). This changes the oil flow in the alarm circuit from the low speed range to the high speed range and connects system oil pressure to drain through high speed oil protection valve (9) and pilot operated two-way valve (23).

2. Oil flow from fuel shutoff sequence valve (24) goes through orifice (14), low speed oil protection valve (8) or high speed oil protection valve (9) and to drain through pilot operated two-way valve (23). This circuit has an oil pressure switch (13), that is normally open. Switch (13) is connected to the alarm circuit oil pressure after orifice (14) and senses the lower system oil pressure. The switch activates an alarm, without engine shutdown, if there is a low engine oil pressure or high coolant temperature condition. (Make reference to Schematic No. 18).

3. Oil from fuel shutoff sequence valve (24) goes to the inlet of diverter valve (18) then to orifice (15) in the valve spool. The oil goes through orifice (15) and goes to the system drain through two-way pilot operated valve (23). The pressure of the oil is lowered after the oil goes through orifice (15), this causes the oil pressure to move the diverter valve spool against a spring force and connect the fuel shutoff actuator oil circuit to the system drain. Thus, the actuator will not shutdown the engine. Engines with electric shutoff solenoids on the governors have a pressure switch installed in the diverter valve outlet for the shutoff actuator. The pressure switch will not shutdown the engine until system oil pressure is directed to it.

Overspeed Circuit (Overspeed Fault)

SCHEMATIC NO. 17 (OVERSPEED FAULT)
2. Emergency manual shutoff valve. 3. Selector valve. 5. Speed sensing valve spool. 8. Low speed oil protection valve. 9. High speed oil protection valve. 10. Oil pump. 11. Oil pressure relief valve. 13. Oil pressure switch. 14. Orifice. 15. Diverter valve orifice. 16. Remote normal shutoff valve. 17. Fuel shutoff actuator. 18. Diverter valve. 19. Engine oil pressure orifice. 20. Start-up override valve. 21. Thermostatic pilot valve. 22. Air inlet sequence valve. 23. Pilot operated two-way valve. 24. Fuel shutoff sequence valve. 25. Air inlet shutoff. 26. Air inlet shutoff actuator.

Make Reference to Schematic No. 17

When the engine speed is 18% above full load speed, speed sensing valve spool (5) will be moved up by the flyweights. This will send oil to pilot operated two-way valve (23) and to the spring side of air inlet sequence valve (22). The oil pressure will close both valves and oil in the air inlet shutoff system can not go to drain. The oil pressure in the system will increase until oil pressure relief valve (11) opens at 1720 kPa (250 psi). The increased pressure will move air inlet shutoff actuator (26), which will release air inlet shutoff valve (25). This stops the combustion air supply to the engine. Fuel shutoff circuit oil also can not go to drain. The difference in oil pressure across orifices (14) and (15) will now go to zero. The valve spool of diverter valve (18) will move down by spring force, which will cause alignment of the ports to the fuel shutoff actuator (17). The blocked oil pressure in the fuel shutoff circuit will activate fuel shutoff actuator (17), which will cause the governor to move the fuel control linkage to the "SHUTOFF" position. Also, oil pressure switch (13) will be closed by the higher pressure oil and will activate an alarm.

When the emergency manual shutoff knob is pulled, system oil flow is directed to pilot operated two-way valve (23) and the spring side of air inlet sequence valve (22). Valve (23) stops oil flow to drain in both the fuel and air inlet shutoff circuits. The protective system then, shuts down the engine in the same sequence as for an overspeed fault condition. The combustion air supply is stopped and the fuel control linkage is moved to the "SHUTOFF" position to shutdown the engine.

Low Oil Pressure Or High Coolant Temperature Fault

SCHEMATIC NO. 18 (LOW OIL PRESSURE OR HIGH COOLANT TEMPERATURE FAULT) (High Speed Range)
3. Selector valve. 5. Speed sensing valve spool. 8. Low speed oil protection valve. 9. High speed oil protection valve. 10. Oil pump. 13. Oil pressure switch. 14. Orifice. 21. Thermostatic pilot valve. 23. Pilot operated two-way valve.

Make Reference to Schematic No. 18

Under normal operation at low engine speeds, the engine oil pressure must be 105 kPa (15 psi) to move low speed oil protection valve (8). The fuel shutoff circuit oil can then flow from pump (10) at 760 kPa (110 psi) through orifice (14), oil pressure switch (13), low speed oil protection valve (8), selector valve (3) and pilot operated two-way valve (23) to drain.

If the engine oil pressure goes below 105 kPa (15 psi), the spring force on low speed oil protection valve (8) will close the valve. The oil flow in the circuit is then stopped and can not flow to drain. The pressure of the oil will become equal on both sides of orifice (14) and oil pressure switch (13) senses 760 kPa (110 psi). The normally open switch closes and activates an alarm.

At approximately 70% of engine full load speed, the oil pressure protection changes from the low speed range to the high speed range.

When the engine speed increases to the high speed range, speed sensing valve spool (5) will be moved up by the flyweights. This will send pilot oil to selector valve (3). This will close selector valve (3) and remove low speed oil protection valve (8) from the circuit. The oil must now flow to drain through high speed oil protection valve (9) and pilot operated two-way valve (23).

If the engine oil pressure decreases to 175 kPa (25 psi), the spring force on high speed oil protection valve (9) will move the valve and stop the oil flow to drain. The pressure of the oil will become equal on both sides of orifice (14) and oil pressure switch (13) senses 760 kPa (110 psi). The normally open switch closes and activates an alarm.

For the engine coolant temperature circuit, a thermostatic pilot valve (21) is connected to the engine oil pressure supply. Thermostatic pilot control valve (21) is normally closed.

NOTE: The sensor of thermostatic pilot valve (21) must be below the water level in the coolant manifold to operate correctly.

When coolant temperature increases to 99°C (210°F), thermostatic pilot valve (21) will open. This will let oil in the circuit go to drain and cause a decrease in engine oil pressure at low speed oil protection valve (8) and high speed oil protection valve (9). The valves close and stop oil flow through orifice (14). The pressure of the oil will become equal on both sides of orifice (14) and oil pressure switch (13) senses 760 kPa (110 psi). The normally open switch closes and activates an alarm.

NOTE: When the engine is started, the low oil pressure - high coolant temperature alarm will be activated for a short time until the engine has enough oil pressure to open low speed oil protection valve (8) or high speed oil protection valve (9).

Remote Normal Shutoff

SCHEMATIC NO. 19 (REMOTE NORMAL SHUTOFF)
15. Diverter valve orifice. 16. Remote normal shutoff valve. 17. Fuel shutoff actuator. 18. Diverter valve. 20. Start-up override valve.

Make Reference to Schematic No. 19

The remote normal shutoff is an option that can be used with the hydramechanical protective system. An air or electric operated remote normal shutoff valve (16) is installed in the diverter valve return line. When remote normal shutoff valve (16) is operated, the outlet of the diverter valve is stopped. The oil pressure becomes equal on both sides of diverter valve orifice (15). Spring force will move the valve spool of diverter valve (18) to make an alignment of the oil passage with the oil line to fuel shutoff actuator (17). Oil pressure can now activate fuel shutoff actuator (17), which causes the governor to move the fuel control linkage to the "SHUTOFF" position and shutdown the engine.