Fig. 7 - Alarm Bell Connected to Electrical
fuel pressure causes the fuel pressure switch to open
the electrical circuit before the decreasing oil pressure
can activate the alarm system.
On 16V-71 engines, coolant protection is also obtained
through an exhaust probe and adaptor assembly and a
temperature switch. In this system, the engine coolant
is circulated around the switch power element to
prevent the switch from being activated by the heat
transfer from the exhaust probe. Therefore, an alarm
Fig. 6 - Alarm System Wiring Diagram
will occur if coolant flow through the adaptor is
interrupted for any reason. The switch will also
an abnormal condition occurs, the engine will be
operate when the engine coolant discharge tempera-
stopped automatically and the alarm hell will ring to
ture exceeds 200-205° F (93-95° C).
notify the operator. The bell will continue to ring until
the operator pushes the reset button on the drop relay.
The oil pressure switch, mounted in the low oil
pressure and overspeed valve (Fig. 8), will be
activated to sound the alarm when the engine oil
The alarm system illustrated in Fig. 8 utilizes the
pressure drops below the safe operating pressure. The
temperature-sensing valve and the low oil pressure
switch will also detect an engine overspeed. Engine oil
and overspeed valve used in the mechanical shutdown
is supplied to the valve. Should the engine oil pressure
drop below a safe operating value, above 1200 rpm,
the valve will operate, dropping the oil pressure at the
switch which completes the circuit and sounds the
When the engine is started, the oil pressure switch will
alarm. Below 1200 rpm the oil pressure switch will
open when the oil pressure reaches 10 psi (69 kPa) and
close whenever the oil pressure is less than the switch
the fuel oil pressure switch will close when the fuel
pressure reaches 20 psi (138 kPa). If overheating or
loss of engine coolant occurs, the temperature-sensing
Engine overspeed is detected by the operation of the
valve will open and permit the oil to flow to the
valve which results in the oil switch closing. The travel
crankcase. The resulting drop in oil pressure will
of the piston in the valve, which is adjustable, controls
permit the contacts in the oil pressure switch to close
the overspeed setting.
and complete the electrical circuit to the alarm bell. A
loss of engine oil pressure or overspeeding of the
The relay is used to prevent damage to the pressure
engine will cause the oil pressure and overspeed valve
and temperature switches should the current to operate
to open and activate the alarm system. Once the alarm
the alarm device be too high.
system is activated, the bell will continue to ring until
the engine operator stops the engine.
Should the alarm be activated for any reason, the
engine should be stopped immediately and the cause
found and corrected before the engine is started again.
During a routine engine shut down, the decreasing