hose, disconnect the battery, and secure the access
When this switch operates, the fuel holding relay is
panels.
de-energized and the engine stops.
The equipment manual for the particular gas
The principal components of the enclosure group
turbine being operated should be consulted for proper
are a starter relay, generator control panel, and an
starting and shutdown procedures.
engine control panel. The engine control panel
provides the operating controls and instruments for
monitoring engine operation.
CAUTION
O I L D R A I N S O L E N O I D VA LV E . -- T h e
If difficulty occurs when starting, do not exceed
normally open oil drain solenoid valve is connected to
the duty cycle of the starter--1 minute ON, 4
a plumbing line from the accessory section; it drains
minutes OFF.
excess oil from the accessory section during
deceleration of the engine or in the event that the inlet
check valve sticks open. When the engine is operating,
SYSTEM OPERATION
the drain solenoid is energized to close.
FUEL SOLENOID VALVE.--The fuel solenoid
With the master (stop-run) switch in the run
valve is a normally closed electromagnetic shutoff
position, power is available to the start switch through
valve, and it is a component of the fuel pump and
the load switch in its OFF position, the test circuit of
control unit. The valve functions to admit or shut off
the load light, th e contacts of the fuel-holding relay,
fuel to the combustion chamber in response to
and the contacts of the starter and ignition-holding
electrical control system operation.
relay. (Refer back to figure 12-8.) Depressing the
momentary contact start switch energizes the coils of
ACCELERATION STABILIZER SOLENOID
the fuel-holding and the starter and ignition-holding
AND ADJUSTABLE ORIFICE ASSEMBLY.--
relays. The fuel-holding relay energizes the oil
The acceleration stabilizer solenoid and adjustable
solenoid drain valve, the fuel side of the oil pressure
orifice assembly is located on the upper compressor
switch, the normally open 95-percent switch, and its
inlet plenum. The assembly consists of a normally
own coil. Ground for the fuel-holding relay coil is
open solenoid valve and an adjustable orifice assembly
through the normally closed 110-percent switch. The
installed in the control air line between the acceleration
starter and ignition-holding relay energizes the starter
thermostat and the fuel pump pneumatic governor. Its
relay, acceleration stabilizer solenoid, load valve
purpose is to stabilize acceleration of the engine by
solenoid, ignition side of the oil pressure switch, and
regulating control air, causing the pneumatic governor
i t s ow n c o i l . G r o u n d f o r t h e s t a r t e r a n d
to bypass fuel and limit engine acceleration rates. The
ignition-holding relay is through the normally closed
solenoid is energized from 0 to 35 percent, and
35-percent switch. The relay energizes the starter
de-energized from 35 to 100 percent unloaded. The
motor, which begins rotating the engine.
solenoid is energized during bleed-load operation
At about 5,000 rpm, rising oil pressure closes the
(100-percent loaded).
oil pressure switch, energizing the ignition unit then
OIL PRESSURE SWITCH.--The oil pressure
the fuel solenoid valve. Combustion is initiated; the
switch is mounted on the back of the compressor
engine begins to accelerate under the combined drives
plenum. It uses two microswitches to initiate ignition
of the starter and combustion until approximately
and fuel flow to the combustion chamber during the
15,000 rpm (35 percent) is reached. At this time the
engine start cycle.
35-percent switch opens the ground circuit to the coil
of the starter and ignition-holding relay, causing it to
PREOPERATIONAL INSPECTION
open. This action de-energizes the starter relay,
ignition unit, acceleration stabilizer solenoid, and the
The preoperational Maintenance Requirements
load valve solenoid. The engine continues to accelerate
Cards require a thorough visual inspection of the unit,
and as approximately 42,000 rpm (95 percent) is
and you should remember that these are the minimum
reached, the 95-percent switch closes, energizing the
requirements prior to starting.
load light (indicating that a load may now be applied),
If any discrepancies exist, take the necessary steps
start counter, and the circuit to the load switch. The
to have them corrected so the unit will be ready for use
engine is loaded by placing the load switch in the ON
position. This energizes the load valve solenoid and the
when it is needed again. Disconnect and stow the air
12-11
