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 HYDRAMECHANICAL PROTECTIVE SYSTEM
SYSTEMS OPERATION
OVERSPEED CIRCUIT (NORMAL
CONDITIONS)
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.
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