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 TM 55-1905-220-14-5
3-65.3. AUTOMATIC ELECTRICAL SHUT-DOWN SYSTEM (Cont).
(2) As the fuel pressure increases upon starting, a diaphragm in the switch body is expanded and forces
the plunger upwards. Since the bottom of the adjusting screw bears against this plunger, the adjusting screw
and the lower breaker point are also forced upwards. When the fuel pressure reaches 20 psi (137.90 kPa) the
breaker points close and the current flows to the terminal of the lubricating oil pressure switch and the water
temperature switch.
(3) When the engine is stopped, the fuel pressure decreases, and the diaphragm in the switch body
contracts. This action causes the plunger to lower and when the fuel oil pressure decreases to 20 psi (137.90
kPa) permits the lower breaker point arm to lower, thus breaking the electrical circuit. The bracket to which the
lower breaker point arm and the adjusting screw are attached is spring loaded which provides for positive
breaking of the points when the fuel pressure decreases sufficiently.
k. Lubricating Oil Pressure Switch.
(1) The lubricating oil pressure switch is similar to the fuel oil pressure switch, except that the fuel oil
pressure switch is of the "make" type while the lubricating oil pressure switch is of the "break" type. In other
words, the lubricating oil pressure switch is calibrated to break contact when the lubricating oil pressure
increases to 10 psi (68.95 kPa). The phrase "10-BREAK" is stamped on the switch cover.
(2) As the lubricating oil pressure increases when the engine starts, the diaphragm in the switch body
expands and forces the plunger upwards. Since the bottom of the adjusting screw bears against the plunger,
and the adjusting screw is attached to the bracket which controls the upper breaker point arm, the arm is also
forced upwards. When the lubricating oil pressure increases to 10 psi (68.95 kPa), the points separate.
However, as previously described, current flows to the lubricating oil pressure switch only after the fuel oil
pressure switch closes. At this time the points of the lubricating oil pressure switch opens. If the lubricating oil
pressure decreases to 10 psi (68.95 kPa) during operation, the breaker point will close and either the alarm bell
or the shut-down solenoid will be energized.
l. Water Temperature Switch.
(1) The terminals of the water temperature switch are connected into the shutdown system and when the
engine circulating water temperature reaches 2055 (96 2.9 ), the switch closes and completes the shut-
F
C
down or alarm system.
3-1150
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