HYDRAMECHANICAL PROTECTIVE SYSTEM
SYSTEMS OPERATION
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. 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.
OVERSPEED CIRCUIT (OVERSPEED FAULT) 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 twoway 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 i crease until oil pressure relief valve (18) opens at 1720kPa (250psi). The increase pressure will move air inlet shutoff actuator (12), which will release the air inlet shutoff valve. This stops the combustion air
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.
224
