system can be shifted to the alternate system. In
the transducer output to 3 kHz for the rotary transformer.
investigating a loss of pitch control on any gas
For a more detailed description of this system's
turbine-powered ship, you must be aware of the
operation, consult the DDG-51 propulsion plant manual
or the CPP system technical manual.
components in the CRP/CPP systems that are most
likely to fail. Let's take a look at some of the components
you will have to monitor most frequently.
CG-47, DD-963, DDG-993, and
FFG-7 Class Ships
ELECTROHYDRAULIC SERVO VALVE. The
most common component failure is the electrohydraulic
With the exception of the previously mentioned
servo valve. This valve is the primary component for
modifications to the CPP system on the DDG-51 class
remote operation and control. If this valve were not
ships, the basic design of the CRP/CPP systems on all
installed, all operations would require personnel to be
gas turbine-powered ships is generally the same. The
stationed at the OD box at all times.
basic operational characteristics are also fundamentally
You can easily identify a faulty electrohydraulic
the same. If you need to review the basic design and
servo valve. Any of the following symptoms should alert
operational characteristics of these systems, we
you as to the possible failure of this valve:
recommend you consult GSE3/GSM3, volumes 1 and 2.
Because of the similarities among these systems, we will
1. The pitch fails to respond to a desired change of
describe in general terms some of the troubleshooting
the integrated throttle control (ITC).
and maintenance tips you can use to monitor and
2. Pitch changes (fluctuations) occur without a
maintain these systems effectively.
pitch change command.
3. There is a steady increase in hub servo pressure
without a change in system demands.
AUXILIARY RELIEF VALVE. A faulty
Even though the CRP/CPP systems installed on a
auxiliary relief valve will also cause a loss of pitch
gas turbine-powered ship use the same types of pumps
control. If the valve fails in the open position, all of the
and fluids as the MRG lube oil system, they are much
control oil will be ported back to the sump. As you
more sophisticated. Paying close attention to system
should know, pitch cannot be changed without control
operating pressures is your most important step in
oil to position the auxiliary servo piston in the OD box.
successfully troubleshooting any problems and making
In addition to the loss of pitch control, you should
the appropriate repairs. The following paragraphs will
investigate any loss of pressure. You should be able to
describe some of the common problems associated with
spot a pressure loss by checking the HOPM pressure
system pressure and the methods you can use to identify
gauges. This should be one of your first steps in
the component or components that might be causing the
checking the system.
problems. Let's first look at two of the most common
casualties that you can identify just by noting variations
REDUCING VALVE. A faulty reducing valve is
in the system pressureloss of pitch control and loss of
another cause for a loss of pitch control. If this valve
hydraulic oil pressure.
happens to fail in the closed position, the flow of control
oil will be cut off to the auxiliary servo piston and pitch
Loss of Pitch Control
will fail to respond. Again, this loss of pressure will have
to be viewed at the HOPM during initial system
A loss of pitch control can be caused by either a
mechanical or an electrical failure. Mechanical failures
will tend to occur more frequently. You should be aware,
Loss of Hydraulic Oil Pressure
however, that electrical problems can occur that will
occasionally produce a loss of control. Normally, an
electrical problem, such as a broken or loose cannon
Usually, a loss of hydraulic oil pressure will cause
plug or loss of feedback position, will require the system
an alarm to be generated at the PACC/PCC. The
to be shifted to manual control. In the case of the
generation of this alarm, of course, will immediately
DDG-51 class ships, however, the CPP system has both
alert the operator of a problem. The alarm will sound
a normal and an alternate system by which the pitch
when casualties occur either to the main relief valve or
position can be monitored. If the normal system should
to a sequencing valve. The alarm will not sound,
fail to provide command or feedback data, the CPP
however, when a major leak occurs. Let's look at the