DETROIT DIESEL
Engine Equipment
Fig. 4 - Automatic Electrical Shut-Down System
Incorporating Hot Wire Relay
Some engines are equipped with an electrically
Fig. 3 - Automatic Electrical Shut-Down System
operated automatic shut-down system which incorpo-
Diagram
rates a hot wire relay (Fig. 4).
the exhaust manifold outlet. Engine water is directed
Since the fuel pressure builds up rapidly, the fuel oil
over the power element of the valve and should the
pressure switch could close before the lubricating oil
water temperature exceed approximately 203 F
pressure switch opens, and effect a shut-down of the
(95 C), the valve will close the contacts in the micro-
engine. The hot wire relay, however, delays the closing
switch and energize the shut-down circuit. If a loss of
of the fuel oil pressure switch for several seconds to
water occurs, the heat of the exhaust gases will be
enable the lubricating oil pressure to build up and
transmitted through the copper plug to the tempera-
open the oil pressure switch contacts.
ture-sensing valve and cause the shut-down circuit to
be activated.
When the lubricating oil pressure falls below 10 2 psi
(69 14 kPa), the contacts in the oil pressure switch
If the engine speed exceeds the high speed setting of
the overspeed governor, the governor switch will close
used in this system will close and current will flow
and activate the shut-down mechanism.
through the hot wire relay to the solenoid. The few
seconds required to heat the hot wire relay provides
When the engine is shut-down, the decrease in speed
sufficient delay to avoid an engine shut-down when low
will open the governor switch, and the decrease in oil
oil pressure is caused by a temporary condition such as
and fuel pressures will close the oil pressure switch and
an air bubble or a temporary overlap in the operation
open the fuel pressure switch, thus de-energizing the
of the oil pressure switch and the fuel oil pressure
circuit.
switch when starting or stopping the engine.
The cause of the abnormal conditions must then be
The water temperature switch, which remains open
determined and corrected before the engine is started
during normal engine operation, is installed in the side
again. Also, the air shut-off valve must be manually
of the thermostat housing. The switch contacts close
reset in the open position before the engine can be
when the water temperature reaches approximately
started.
205 F (96 C) and activate the shut-down solenoid.
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