HYDRAMECHANICAL PROTECTIVE SYSTEM
OVERSPEED CIRCUIT (OVERSPEED FAULT)
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 in- crease 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.
combustion air supply is stopped and the fuel
control linkage is moved to the "SHUTOFF"
position to shutdown the engine.