ARMY TM 9-6115-464-34
AIR FORCE TO 35C2-3-445-2
NAVY NAVFAC P-8-624-34
3-7. SPEED SWITCH.
The speed switch provides sequenced control of circuits during engine startup, and protection
against engine overspeed during operation. Three sets of contact elements, S9-1, S9-2, and S9-3,
contained in the speed switch, are set to open, close, or transfer at certain engine speeds. The
speed switch drive gear is designed to drive the speed switch at one-half engine speed.
At an engine speed of 580 to 620 rpm (accelerating) element S9-1 transfers two sets of contacts,
energizing the field flash circuit and de-energizing the crank relay to stop the starting motor.
On tactical precise sets, when the engine reaches the speed range of 1180 to 1220 rpm (50/60 Hz),
1650 to 1700 rpm (400 Hz), element S9-2 closes, energizing the electrohydraulic governor which
takes over control of engine speed.
Speed switch element S9-3 consists of two sets of contacts which are set to transfer at an engine
speed of 2425 ± 25 rpm to shut down the engine and prevent damage to the equipment. Shutdown is
achieved by de-energizing the stop-run relay and the fuel solenoid, cutting off fuel to the engine.
Elements S9-1 and S9-2 reset at 100 rpm (decreasing) below actuation speed. Element S9-3 is
manually reset by a pushbutton on the speed switch housing.
Figure 3-14. Output and Voltage Protector Test.