1-14. MISCELLANEOUS CONTROL DEVICES (cont)
(3) ENGINE RUN RELAY (ER). An interlock relay that controls the coil circuit of the magnetic valves in the throttle
(4) THROTTLE OPERATOR (TO). This electro-pneumatic device consists of four magnet valves and air cylinders, the
pistons of which are connected to the speed adjusting shaft of the engine governor. The unit is used to vary the
engine governor speed setting. It is electrically controlled by the controller mechanism, its magnet valves being
energized in seven successive combinations as the throttle handle is moved from notch two to eight. When the
throttle handle is in notch one, the engine will run at idle speed. As the throttle handle is advanced, the engine speed
will increase until full engine speed is obtained in notch eight.
(5) ISOLATION SWITCH (IS). This rotary switch has two positions: IDLE and RUN. The switch is set to IDLE when
starting the diesel engine. It can also be set to IDLE to permit the diesel engine of a locomotive unit to idle when it is
coupled for multiple unit control and is being-towed (deadheading). This position serves to isolate a unit when
operating under extremely cold climatic conditions. This allows the engine to maintain its normal operating
temperature, charge the batteries, and pump air. The run position is used for normal operation of the locomotive as
a single unit and also used in multiple operation when two or more units are coupled (train-lined). In the run position,
the isolation switch helps control the coil circuit of the engine run relay, the battery field, and shunt field contactors.
(6) FUEL PRESSURE CONTROL (FPC). An interlock relay that controls the coil circuit of the fuel shutdown magnetic
valve and helps control the coil circuit of the engine run relay.
(7) PRESSURE CONTROL RELAY (PCR). An interlock relay that helps control the coil circuit of the shunt field and the
battery field relays; energizes when proper air pressure is obtained.
(8) CLOSE DOWN RELAY (CDR). This relay is energized when the throttle is in positions 3 thru 8. In throttle position
STOP, the relay is deenergized and sends voltage to the coil circuit of the governor shutdown relay. This shuts down
the diesel engine.
(9) TIMER RELAY (TR). This timing device cycles the four electric drain valves. There is one valve on the bottom of
each of the main reservoir air tanks, and one each on top of the main reservoir air filter and the secondary air filter.
When input power is applied to the timer relay a timing cycle will cause a short and long blast of air at the drain valves
every 3 minutes.