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pressurized with dry nitrogen to 700 psig for the high-
Gyro Signal Card Assembly
-pressure accumulator and 38 psig for the low-pressure
The gyro signal card (F106) amplifies and sums the
demodulated pitch and roll synchro signals from the
When hydraulic pressure is applied, the accumula-
ship's gyro with the platform LVDT outputs. It also
tor falls with fluid and the bladder is compressed until
provides offset adjustments to make up for any
the dry nitrogen charge pressure equals that of the
difference in alignment between the ship's gyro and
hydraulic system. In this system, it is 1400 psig. Because
platform. In addition, rate lead signals are derived by
of the bladder compression, the accumulator will absorb
differentiating the ship gyro signals.
pressure fluctuations and prevent hydraulic hammer. If
the system momentarily requires a higher flow than the
Source Light Failure Detector
pump will supply, the accumulator will provide it and
be recharged when the demand has passed.
The source light failure detector is a circuit that
monitors the voltage and current going to the three
Hydraulic Cylinder
source lights. When one or more of the source lamps
fail, the source light failure indicator on the remote panel
The hydraulic cylinders used in this system are
is illuminated
linear actuators. Hydraulic fluid gaited by the servo
valve will push the piston in either direction. The
Power Distribution Circuits
hydraulic pressure exerted by the piston is 1400 psig in
extension and 700 psig in compression. Extreme care
The system requires two power sources from the
must be exercised when working on the system due to
ship 440-volts ac, 60-Hz, 2.7-amp power for the pump
the amount of force available.
and 115-volts ac, 60-HZ, 15-amp power for the rest of
The cylinder is an inherently reliable device requir-
the system. In standby (system circuit breaker on), the
ing little maintenance in normal use. However, the only
system heaters and standby lights are on. When the
required maintenance is cleaning dirt and grit off the
POWER ON push buttons are depressed, the internal
actuator rod and tightening the packing gland nut if a
power supplies are energized except for the 15 volts
leak develops. Do not overtighten the gland nut or the
dc. The 15 volts dc supply is energized after the time
packing will bind on the rod, causing the cylinder to
delay relay has timed out, the hydraulic pump is running,
chatter in operation. If cylinder replacement becomes
and system hydraulic pressure is normal. Then, the
necessary, the defective cylinder must be returned
hydraulic pressure switch is actuated.
through supply charnels for overhaul.
System low-amplitude vibration, or chatter in some
cases, may be traceable to cylinder internal binding; in
The SGSI system uses hydraulic pressure for
which case the cylinder should be replaced.
motive power. A constant-pressure, variable-delivery
hydraulic pump supplies hydraulic pressure. Pressure
Servo Valve
fluctuations are dampened by accumulators. The fluid
is gaited by servo valves into either side of the hydraulic
Servo valves are commonly used in closed-loop
cylinders. The fluid pressure then causes the cylinders
servo systems. They control the flow of fluid to or from
to move the platform.
the load actuator in proportion to the impact current
signal to the valves' torque motor.
The hydraulic system is sensitive to dirt and other
contaminants. Therefore, care must be used when
Hydraulic Pump
adding fluid or opening any part of the hydraulic system.
Refer to the hydraulic pump assembly shown in
The hydraulic pump used in this system is a con-
figure 3-9 when studying the following paragraphs.
stant-pressure, variable-delivery pump. It is similar to a
constant voltage source in which current will vary upon
Hydraulic Accumulator
demand. Referring to figure 3-9, hydraulic fluid is
gravity fed from the reservoir to the pump unit through
The hydraulic accumulators used in this system are
the pump case fill piping to ensure that the pump case is
steel cylinders with internal rubber bladders. Before
full at all times, thus keeping air out of the line. The
motor-driven pump draws fluid through a suction
putting the accumulators in service, the bladders are

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