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 TM 55-1905-220-14-5
3-65.3. AUTOMATIC ELECTRICAL SHUT-DOWN SYSTEM (Cont).
contacts close before the lubricating oil pressure reaches 10 psi (68.95 kPa). This condition normally would
cause the engine to shutdown, except for the introduction of a time delay relay into the circuit. This relay
delays the energizing of the shut-down solenoid by 3 to 10 seconds, enabling the lubricating oil pressure to
exceed 10 psi (68.95 kPa) thereby opening the lubricating oil pressure switch and preventing the energizing of
the circuit. When the engine has reached normal operating speed, the lubricating oil pressure switch is open.
f. When the lubricating oil pressure falls below 102 psi (68.9513.8 kPa), the oil pressure switch closes
and the current flows to the time delay relay which must be heated by the current to complete the circuit to the
solenoid. The few seconds required to heat the time delay relay provides sufficient delay to avoid engine shut-
down when low oil pressure is caused by a passing condition such as an air bubble or by the temporary overlap
in the operation of the lubricating oil pressure switch and fuel pressure switch during starting and stopping of
the engine.
NOTE
An alarm will sound in the pilothouse.
g. The high water temperature switch is connected in parallel with the lubricating oil pressure switch and
normally remains open, closing only when the engine coolant temperature exceeds 200 5 (93.3 2.8 ),
F
C
thus energizing the shut-down solenoid.
NOTE
An alarm will sound in the pilothouse.
h. The overspeed governor is driven by the blower drive shaft. If the engine speed exceeds the speed
which has been established by the engine governor, the overspeed governor switch is actuated, causing the
shut-down solenoid to close the shut-down valve.
i. When the engine is shut-down, as described above, the fuel oil pressure switch opens, thus breaking
the circuit and eliminating the possibility of damage due to continued exposure to current.
j. Fuel Oil Pressure Switch.
(1) The fuel oil pressure switch is the controlling switch of the system, since this switch controls the flow
of current to the other two switches. The fuel oil pressure switch is set to make contact when the fuel pressure
reaches 20 psi (137.90 kPa) and the phrase "20-MAKE" is stamped on the switch cover.
3-1149
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