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 TM 55-1905-242-14
0009 00
Alarm Bells
The general alarm system has two alarm bells. One is located in the accommodation module; the other is located in the engine
room. When the pilothouse rotary switch is closed (ON), current flows to the alarm bells and they ring.
Rotary Switch
A rotary switch, located on the pilothouse overhead above the coxswain's seat, controls the general alarm system. When the
switch is closed (ON), current flows to the alarm bells and they ring.
General Alarm Junction Box
The general alarm junction box, located on bulkhead 31, port of centerline, in the engine room, connects the rotary switch
and the two alarm bells. The junction box also contains four fuses that protect the system from damage due to overload.
ENGINE ALARM SYSTEM
General
The engine alarm system warns the operator of low engine oil pressure and high engine coolant temperature conditions for
the propulsion engines. When engine oil pressure falls too low, or coolant temperature rises too high, lights illuminate on the
pilothouse console to warn the operator of the condition. The system is powered by 24 Vdc from the control and distribution
panel in the pilothouse. The system is composed of Fuel Pressure (FP) switches, Low Oil Pressure (LOP) switches, High
Water Temperature (HWT) switches, and alarm lights. The schematic on the following page details system operation.
Fuel Pressure Switch
Two normally-open fuel pressure switches are installed in the system, one for each Low Oil Pressure (LOP) or High Water
Temperature (HWT) circuit. These switches arm and disarm the LOP alarm system. When the engine is running, fuel
pressure is present, and the fuel pressure switches close, arming the LOP alarm system. When the engine is secured, fuel
pressure is absent, and the switches open, disarming the system. This automatic disarming of the alarm system prevents the
engine alarms from activating when the engines are secured.
Oil Pressure Switch
Each propulsion engine has a normally-closed, Low Oil Pressure (LOP) switch for the alarm system. When engine oil
pressure is below the switch's closing pressure, the switch closes. If the engine is running (fuel pressure switch closed), the
electrical circuit to the alarm light in the pilothouse console is completed, and the light illuminates. Under normal engine
operating conditions, the oil pressure switch is open, the fuel pressure switch is closed, and the alarm light is off.
Coolant Temperature Switch
Each propulsion engine has a normally-open, High Water Temperature (HWT) switch for the alarm system. When the engine
coolant temperature rises above the switch's closing temperature, the switch closes. With the switch closed, the electrical
circuit to the alarm light in the pilothouse console is completed, and the light illuminates. Under normal engine operating
conditions, the high water temperature switch is open, and the alarm light is off.
Alarm Light
Four alarm lights, one for each alarm circuit, are installed in the pilothouse console. When the necessary switches in a given
alarm circuit are closed, the alarm light's electrical circuit is complete, and the alarm light illuminates.
0009 00-3
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