The pressure of the oil entering the bellows overcomes
the tension of the bellows spring and permits the latch to
retain the air shut-off valve in the open position. If the
To start an engine equipped with a mechanical
oil pressure drops below a predetermined value, the
shutdown system, first manually open the air shut-off
spring in the bellows will release the latch and permit the
valve and then press the engine starting switch. As
air shut-off valve to close and thus stop the engine.
soon as the engine starts, the starting switch may be
released, but the air shut-off valve must be held in the
The overspeed governor, used on certain applications,
open position until the engine oil pressure increases
consists of a valve actuated by a set of spring-loaded
sufficiently to permit the bellows to retain the latch in the
weights. Engine oil is supplied to the valve through a
connection in the oil line between the bellows and the
temperature-sensing valve. An outlet in the governor
During operation, if the engine oil pressure drops below
valve is connected to the engine oil sump. Whenever
the setting of the pressure sensitive bellows, the spring
the engine speed exceeds the overspeed governor
within the bellows will release the latch and permit the
setting, the valve (actuated by the governor weights) is
air shut-off valve to close, thus stopping the engine.
moved from its seat and permits the oil to flow to the
engine sump. This decreases the oil pressure to the
If the engine coolant overheats, the temperature-
bellows, thus actuating the shut-down mechanism and
sensing valve will open and permit the oil in the
stopping the engine.
protective system to flow to the engine crankcase. The
resulting decrease in oil pressure will actuate the
A restricted fitting, which will permit a drop in oil
shutdown mechanism and stop the engine. Also if the
pressure great enough to actuate the shut-down
engine loses its coolant, the copper plug will be heated
mechanism, is required in the oil line between the
up by the hot exhaust gases passing over it and cause
cylinder block oil gallery and the shut-down sensing
the temperature-sensing valve to open and actuate the
To be sure the protective system will function properly if
Whenever the engine speed exceeds the overspeed
an abnormal engine condition occurs, have the system
governor (if used) setting, the oil in the line flows to the
checked periodically by your local Detroit Diesel Allison
sump, resulting in a decrease in oil pressure. The oil
pressure bellows then releases the latch and permits the
air shut-off valve to close.
Also make sure the air shut-off valves close each time
When an engine is stopped by the action of the
the engine is shut down.
shutdown system, the engine cannot be started again
until the particular device which actuated the shut-down
mechanism has returned to its normal position. The
abnormal condition which caused the engine to stop
must be corrected before attempting to start it again.
AUTOMATIC ELECTRICAL SHUT-DOWN SYSTEM
The automatic electrical shut-down system shown in Fig.
3 protects the engine against a loss of coolant,
If the oil pressure drops below 10 psi, the oil pressure
overheating of the coolant, loss of oil pressure, or
switch will close the circuit and energize the shut-down
In the event one of the foregoing
solenoid. This will activate the shut-down mechanism
conditions arises, a switch will close the electrical circuit
and stop the engine.
and energize the solenoid switch, causing the shut-down
solenoid to release the air shut-down latch and stop the
A loss of coolant or an increase in coolant temperature
to approximately 203 F. will close the contacts in the
water temperature switch, thus dosing the electrical
circuit and activating the shut-down mechanism.
The water temperature switch consists of a temperature-
The electrical circuit is de-energized under normal
sensing valve and a micro-switch. The valve contacts a
operating conditions. When the engine is started, the oil
copper plug (heat probe) which extends into the exhaust
pressure switch opens when the oil pressure reaches
manifold outlet. Engine water is directed
approximately 10 psi and the fuel oil pressure switch
Page 34 closes at approximately 20 psi fuel pressure.
The water temperature switch remains open.