DETROIT DIESEL
Engine Equipment
The pressure of the oil entering the bellows overcomes
Operation
the tension of the bellows spring and permits the latch
To start an engine equipped with a mechanical shut-
to retain the air shut-off valve in the open position. If
down system, first manually open the air shut-off valve
the oil pressure drops below a predetermined value,
and then press the engine starting switch. As soon as
the spring in the bellows will release the latch and
the engine starts, the starting switch may be released,
permit the air shut-off valve to close and thus stop the
but the air shut-off valve must be held in the open
engine.
position until the engine oil pressure increases
sufficiently to permit the bellows to retain the latch in
the open position.
The overspeed governor, used on certain applications,
consists of a valve actuated by a set of spring-loaded
During operation, if the engine oil pressure drops
weights. Engine oil is supplied to the valve through a
below the setting of the pressure sensitive bellows, the
connection in the oil line between the bellows and the
spring within the bellows will release the latch and
temperature-sensing valve. An outlet in the governor
permit the air shut-off valve to close, thus stopping the
valve is connected to the engine oil sump. Whenever
engine.
the engine speed exceeds the overspeed governor
If the engine coolant overheats, the temperature-
setting, the valve (actuated by the governor weights) is
sensing valve will open and permit the oil in the
moved from its seat and permits the oil to flow to the
protective system to flow to the engine crankcase. The
engine sump. This decreases the oil pressure to the
resulting decrease in oil pressure will actuate the shut-
bellows, thus actuating the shut-down mechanism and
down mechanism and stop the engine. Also if the
stopping the engine.
engine loses its coolant, the copper plug will be heated
up by the hot exhaust gases passing over it and cause
the temperature-sensing valve to open and actuate the
A restricted fitting, which will permit a drop in oil
shut-down mechanism.
pressure great enough to actuate the shut-down
mechanism, is required in the oil line between the
Whenever the engine speed exceeds the overspeed
cylinder block oil gallery and the shut-down sensing
governor (if used) setting, the oil in the line flows to
devices.
the sump, resulting in a decrease in oil pressure. The
oil pressure bellows then releases the latch and permits
To be sure the protective system will function properly
the air shut-off valve to close.
if an abnormal engine condition occurs, have the
When an engine is stopped by the action of the shut-
system checked periodically by your local Detroit
down system, the engine cannot be started again until
Diesel Allison Service Outlet.
the particular device which actuated the shut-down
mechanism has returned to its normal position. The
Also make sure the air shut-off valves close each time
abnormal condition which caused the engine to stop must
the engine is shut down.
be corrected before attempting to start it again.
AUTOMATIC ELECTRICAL SHUT-DOWN SYSTEM
The automatic electrical shut-down system shown in
switch closes at approximately 20 psi (138 kPa) fuel
Fig. 3 protects the engine against a loss of coolant,
pressure. The water temperature switch remains open.
overheating of the coolant, loss of oil pressure, or
overspeeding. In the event one of the foregoing
If the oil pressure drops below 10 psi (69 kPa), the oil
conditions arises, a switch will close the electrical
pressure switch will close the circuit and energize the
circuit and energize the solenoid switch, causing the
shut-down solenoid. This will activate the shut-down
shut-down solenoid to release the air shut-down latch
mechanism and stop the engine.
and stop the engine.
A loss of coolant or an increase in coolant temperature
to approximately 203 F (95 C) will close the contacts
in the water temperature switch, thus closing the
Operation
e l e c t r i c a l circuit and activating the shut-down
mechanism.
The electrical circuit is de-energized under normal
The water temperature switch consists of a tempera-
operating conditions. When the engine is started, the
ture-sensing valve and a micro-switch. The valve
oil pressure switch opens when the oil pressure reaches
contacts a copper plug (heat probe) which extends into
approximately 10 psi (69 kPa) and the fuel oil pressure
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