SHUTOFF AND ALARM SYSTEMS
The engine speed is felt by magnetic pickup (1). As the
teeth of the flywheel go through the magnetic lines of
force around the pickup, an AC voltage is made. Dual
speed switch (3) measures engine speed from the
frequency of this AC voltage.
Time delay relay (4) controls the operation of
shutdown relay (6), which in turn, controls the operation
of fuel shutoff solenoid (9). Time delay relay (4) will keep
the fuel shutoff solenoid energized for 70 seconds after a
fault condition. This prevents the engine from being
started again before the flywheel has stopped rotation.
When the engine starts and gets to a speed just
above cranking speed, the normally open contacts of
crank terminate switch (2) [which is part of dual speed
switch (3)] will close. This will complete the circuit to time
delay relay (4) through terminal TD-I. Normally open
switch (5) in time delay relay (4) now closes and
completes the circuit between shutdown relay (6) and
If the engine speed increases above the
overspeed setting (118% of rated speed) of the dual
speed switch, the overspeed switch (part of the dual
speed switch) will close across terminals DSS-7 and
DSS-8. This completes the circuit to shutdown relay (6)
through the now closed switch (5) at terminal TD-7.
Shutdown relay (6) is activated and in turn activates fuel
shutoff solenoid (9) to cause the engine to shutdown.
When the engine stops, crank terminate switch
(2) will open the circuit across terminals DSS-IO and
DSS1 1. This stops current flow to time delay relay (4).
Now, the time delay relay timer is started and 70
seconds later, switch (5) will open the circuit at terminal
TD-7. Current flow is then stopped through shutdown
relay (6) and fuel shutoff solenoid (9) will no longer be
A reset button on the dual speed switch must be
pushed to open the overspeed switch before the engine
To help prevent damage to the
engine, find and correct the problem that caused the
engine to overspeed, before the engine is started