SHUTOFF AND ALARM SYSTEMSSYSTEMS OPERATIONThe engine speed is felt by magnetic pickup (1). As theteeth of the flywheel go through the magnetic lines offorce around the pickup, an AC voltage is made. Dualspeed switch (3) measures engine speed from thefrequency of this AC voltage.Time delay relay (4) controls the operation ofshutdown relay (6), which in turn, controls the operationof fuel shutoff solenoid (9). Time delay relay (4) will keepthe fuel shutoff solenoid energized for 70 seconds after afault condition. This prevents the engine from beingstarted again before the flywheel has stopped rotation.When the engine starts and gets to a speed justabove cranking speed, the normally open contacts ofcrank terminate switch (2) [which is part of dual speedswitch (3)] will close. This will complete the circuit to timedelay relay (4) through terminal TD-I. Normally openswitch (5) in time delay relay (4) now closes andcompletes the circuit between shutdown relay (6) andterminal TD-7.If the engine speed increases above theoverspeed setting (118% of rated speed) of the dualspeed switch, the overspeed switch (part of the dualspeed switch) will close across terminals DSS-7 andDSS-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 fuelshutoff solenoid (9) to cause the engine to shutdown.When the engine stops, crank terminate switch(2) will open the circuit across terminals DSS-IO andDSS1 1. This stops current flow to time delay relay (4).Now, the time delay relay timer is started and 70seconds later, switch (5) will open the circuit at terminalTD-7. Current flow is then stopped through shutdownrelay (6) and fuel shutoff solenoid (9) will no longer beactivated.A reset button on the dual speed switch must bepushed to open the overspeed switch before the enginewill run.NOTICETo help prevent damage to theengine, find and correct the problem that caused theengine to overspeed, before the engine is startedagain.27
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