TM 5-3820-245-14&P
If the engine speed exceeds the high speed setting of the overspeed governor, the governor switch will close and activate
the shutdown mechanism.
When the engine is shut down, the decrease in speed will open the governor switch and the decrease in oil and fuel
pressures will close the oil pressure switch, and open the fuel pressure switch, thus de-energizing the circuit.
The cause of the abnormal conditions must then be determined and corrected before the engine is started again. Also,
the air shutoff valve must be manually reset in the open position before the engine can be started.
Since the fuel pressure builds up rapidly,-the fuel oil pressure switch could close before the lubricating oil pressure switch
opens and stop the engine. The hot wire relay, however, delays the closing of the fuel oil pressure switch for several
seconds to enable the lubricating oil pressure to build up and open the oil pressure switch contacts.
When the lubricating oil pressure falls below 10+2 psi (69+14 kPa), the contacts in the oil pressure switch used in this
system will close and current will flow through the hot wire relay to the solenoid. The few seconds required to heat the hot
wire relay provides sufficient delay to avoid stopping the engine when low oil pressure is caused by a temporary condition
such as an air bubble or a temporary overlap in the operation of the oil pressure switch and the fuel oil pressure switch
when starting or stopping the engine.
The water temperature switch, which remains open during normal engine operation, is installed in the side of the
thermostat housing. The switch contacts close when the water temperature reaches approximately 205F (96C) and
activate the shutdown solenoid.
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